Water Bourne Diseases

WORLD HEALTH ORGANIZATION

Anaemia

Anaemia is common throughout the world. Its main cause, iron deficiency, is the most prevalent nutritional deficiency in the world. Several infections related to hygiene, sanitation, safe water and water management are significant contributors to anaemia in addition to iron deficiency. These include malaria, schistosomiasis and hookworm.

The disease and how it affects people

Anaemia is a condition that occurs when the red blood cells do not carry enough oxygen to the tissues of the body. Anaemia affects all population groups. However the most susceptible groups are pregnant women and young children. In the milder form, anaemia is “silent”, without symptoms. In the more severe form, anaemia is associated with fatigue, weakness, dizziness and drowsiness. The signs include loss of normal colour in the skin (in fair skinned people) and also in the lips, tongue nail beds and the blood vessels in the white of the eye. Without treatment, anaemia can worsen and become an underlying cause of chronic ill health, such as impaired fetal development during pregnancy, delayed cognitive development and increased risk of infection in young children, and reduced physical capacity in all people. Low birth weight infants, young children and women of childbearing age are particularly at risk of anaemia. Women of childbearing age need to absorb 2-3 times the amount of iron required by men or older women.

The cause

The main causes of anaemia are nutritional and infectious. They usually coexist in the same individual and make anaemia worst.

Among the nutrition factors contributing to anaemia, the most common one is iron deficiency. It is due to a diet that is monotonous, but rich in substances (phytates) inhibiting iron absorption so that dietary iron cannot be utilised by the body. Iron deficiency may also be aggravated by poor nutritional status, especially when it is associated with deficiencies in folic acid, vitamin A or B12, as is often the case in populations living in developing countries

With regard to infections, malaria is another major cause of anaemia : it affects 300-500 million people, and in endemic areas it may be the primary cause of half of all severe anaemia cases (WHO, 2000). Hookworm infection and in some places schistosomiasis also contribute to anaemia. Approximately 44 million pregnant women have hookworm infections and 20 million people are severely infected with schistosomiasis. Anaemia can also be due to excessive blood loss, such as gastrointestinal infections associated with diarrhoea. The most important water-related causes of anaemia are malnutrition and water-borne or water-related infections.

Distribution

Anaemia is a common problem throughout the world and iron deficiency is the most prevalent nutritional deficiency in the world. It affects mainly the poorest segment of the population, particularly where malnutrition is predominant and the population exposed to a high risk of water-related infection.

Scope of the problem

Nine out of ten anaemia sufferers live in developing countries, about 2 billion people suffer from anaemia and an even larger number of people present iron deficiency (WHO, 2000). Anaemia may contribute to up to 20% of maternal deaths.

Intervention

Full discussion of strategies towards anaemia prevention are beyond the scope of this Fact Sheet. Because anaemia is the result of multiple factors, the identification of these factors and of the causes and type of anaemia is important. Important actions include addressing underlying causes correcting iron deficiency, treatment of underlying disease processes (in particular nutritional deficiencies - Folic acid, Vitamin A and B12).

In children, promoting breastfeeding and proper complementary foods are important in controlling anaemia.

Improving hygiene, sanitation and water supply; and improving water resource management to contribute to control of schistosomiasis and malaria where they occur are important contributory measures in prevention of anaemia.

Reference

WHO. Turning the tide of malnutrition: responding to the challenge of the 21st century. Geneva: WHO, 2000 (WHO/NHD.007)

Prepared for World Water Day 2001. Reviewed by staff and experts in the Department of Nutrition for Health and Development (NHD) and the Water, Sanitation and Health Unit (WSH), World Health Organization (WHO), Geneva.

Arsenicosis

Drinking water rich in arsenic over a long period leads to arsenic poisoning or arsenicosis. Many waters contain some arsenic and excessive concentrations are known to naturally occur in some areas. The health effects are generally delayed and the most effective preventive measure is supply of drinking water low in arsenic concentration.

The disease and how it affects people

Arsenicosis is the effect of arsenic poisoning, usually over a long period such as from 5 to 20 years. Drinking arsenic-rich water over a long period results in various health effects including skin problems (such as colour changes on the skin, and hard patches on the palms and soles of the feet), skin cancer, cancers of the bladder, kidney and lung, and diseases of the blood vessels of the legs and feet, and possibly also diabetes, high blood pressure and reproductive disorders.

Absorption of arsenic through the skin is minimal and thus hand-washing, bathing, laundry, etc. with water containing arsenic do not pose human health risks.

In China (Province of Taiwan) exposure to arsenic via drinking-water has been shown to cause a severe disease of the blood vessels, which leads to gangrene, known as ‘black foot disease’. This disease has not been observed in other parts of the world, and it is possible that malnutrition contributes to its development. However, studies in several countries have demonstrated that arsenic causes other, less severe forms of peripheral vascular disease.

The cause

Arsenicosis is caused by the chemical arsenic. Arsenic is a toxic element that has no apparent beneficial health effects for humans.

Natural arsenic salts are present in all waters but usually in only very small amounts. Most waters in the world have natural arsenic concentrations of less than 0.01 mg/litre.

Arsenicosis is caused by exposure over a period of time to arsenic in drinking water. It may also be due to intake of arsenic via food or air. The multiple routes of exposure contribute to chronic poisoning. Arsenic contamination in water may also be due to industrial processes such as those involved in mining, metal refining, and timber treatment. Malnutrition may aggravate the effects of arsenic in blood vessels.

WHO's Guideline Value for arsenic in drinking water is 0.01 mg /litre. This figure is limited by the ability to analyse low concentrations of arsenic in water.

Distribution

Natural arsenic contamination is a cause for concern in many countries of the world including Argentina, Bangladesh, Chile, China, India, Mexico, Thailand and the United States of America.

Scope of the Problem

Because of the delayed health effects, poor reporting, and low levels of awareness in some communities, the extent of the adverse health problems caused by arsenic in drinking-water is unclear and not well documented. As a result there is no reliable estimate of the extent of the problem worldwide. WHO is presently collecting information in order to make such an estimate.

Case reports on the situation in various countries have been compiled and the arsenic problem in Bangladesh in particular has prompted more intensive monitoring in many other countries. In Bangladesh, 27 % of shallow tube-wells have been shown to have high levels of arsenic (above 0.05mg/l). It has been estimated that 35 - 77 million of the total population of 125 million of Bangladesh are at risk of drinking contaminated water (WHO bulletin, volume 78, (9):page 1096). Approximately 1 in 100 people who drink water containing 0.05 mg arsenic per litre or more for a long period may eventually die from arsenic related cancers.

Interventions

The most important action in affected communities is the prevention of further exposure to arsenic by provision of safe drinking-water. Arsenic-rich water can be used for other purposes such as washing and laundry. In the early stages of arsenicosis, drinking arsenic-free water can reverse some of the effects. Long term solutions for prevention of arsenicosis include:

For provision of safe drinking-water:

• Deeper wells are often less likely to be contaminated.
• Rain water harvesting in areas of high rainfall such as in Bangladesh. Care must be taken that collection systems are adequate and do not present risk of infection or provide breeding sites for mosquitoes.
• Use of arsenic removal systems in households (generally for shorter periods) and before water distribution in piped systems.
• Testing of water for levels of arsenic and informing users.

In order to effectively promote the health of people the following issues should be taken into account:

• Monitoring by health workers - people need to be checked for early signs of arsenicosis - usually skin problems in areas where arsenic in known to occur.
• Health education regarding harmful effects of arsenicosis and how to avoid them.

References

Arsenic in Drinking Water. WHO Fact Sheet No. 210. Revised May 2001.

Bulletin of the World Health Organization, volume 78, (9):page 1096

Prepared for World Water Day 2001. Reviewed by staff and experts from the Programme for Promotion of Chemical Safety (PCS), and the Water, Sanitation and Health unit (WSH), World Health Organization (WHO), Geneva

Ascariasis

The disease and how it affects people

Ascariasis is an infection of the small intestine caused by Ascaris lumbricoides, a large roundworm. The eggs of the worm are found in soil contaminated by human faeces or in uncooked food contaminated by soil containing eggs of the worm. A person becomes infected after accidentally swallowing the eggs. The eggs hatch into larvae within the person's intestine. The larvae penetrate the intestine wall and reach the lungs through the blood stream. They eventually get back to the throat and are swallowed. In the intestines, the larvae develop into adult worms. The female adult worm which can grow to over 30cm in length, lays eggs that are then passed into the faeces. If soil is polluted with human or animal faeces containing eggs the cycle begins again. Eggs develop in the soil and become infective after 2-3 weeks, but can remain infective for several months or years.

Children are infected more often than adults, the most common age group being 3-8 years. The infection is likely to be more serious if nutrition is poor. They often become infected after putting their hands to their mouths after playing in contaminated soil. Eating uncooked food grown in contaminated soil or irrigated with inadequately treated wastewater is another frequent avenue of infection.

The first sign may be the passage of a live worm, usually in the faeces. In a severe infection, intestinal blockage may cause abdominal pain, particularly in children. People may also experience cough, wheezing and difficulty in breathing, or fever.

Distribution

Ascariasis is found worldwide. Infection occurs with greatest frequency in tropical and subtropical regions, and in any areas with inadequate sanitation.

Scope of the Problem

Ascariasis is one of the most common human parasitic infections. Up to 10% of the population of the developing world is infected with intestinal worms – a large percentage of which is caused by Ascaris. Worldwide, severe Ascaris infections cause approximately 60,000 deaths per year, mainly in children.

Interventions

Health education providing the following messages reduces the number of infected people:

1.       avoid contact with soil that may be contaminated with human faeces;

2.       wash hands with soap and water before handling food;

3.       wash, peel or cook all raw vegetables and fruits;

4.       protect food from soil and wash or reheat any food that falls on the floor.

The availability of water for use in personal hygiene as well as proper disposal of human faeces will also reduce the number of cases. Where wastewater is used for irrigation waste stabilization ponds and some other technologies are effective in decreasing transmission due to food grown in contaminated soil.

Infected individuals (and domestic animals) should be treated with medicine to reduce disease transmission. Ascariasis can be effectively treated with mebendazole or pyrantel pamoate.

Written for World Water Day2001. Reviewed by staff and experts from the cluster on Communicable Diseases (CDS) and Water, Sanitation and Health unit (WSH), World Health Organization (WHO).

WHO/WSH/WWD/DFS.01

Campylobacteriosis

Campylobacteriosis is a severe form of diarrhoea that occurs worldwide. Sanitation, personal and food hygiene as well as safe water supply are important in its prevention.

The disease and how it affects people

Campylobacteriosis is an infection of the gastrointestinal tract. Symptoms of the infection include diarrhoea (often including the presence of mucus and blood), abdominal pain, malaise, fever, nausea and vomiting. The illness usually lasts 2 to 5 days but may be prolonged by relapses, especially in adults. Many of those infected show no symptoms. In some individuals a reactive arthritis (painful inflammation of the joints) can occur. Rare complications include seizures due to high fever or neurological disorders such as Guillain-Barre syndrome or meningitis. Death from campylobacteriosis is rare and is more likely in the very young, the very old, or those already suffering from a serious disease such as AIDS.

The cause

Campylobacteriosis is a zoonosis (passed to humans via animals or animal products). The cause is a bacterium, usually Campylobacter jejuni or C. coli. The bacteria are widely distributed and found in most warm-blooded domestic and wild animals. They are common in food animals such as poultry, cattle, pigs, sheep, ostriches, and shellfish and in pets including cats and dogs. The animals may not have symptoms. People are exposed to the bacteria after consuming contaminated food such as undercooked meats, contaminated water, or raw milk.

Distribution

The Campylobacter are generally regarded as one of the most common bacterial cause of gastroenteritis worldwide. In both developed and developing countries, they cause more cases of diarrhoea than Salmonella bacteria. In developed countries, the disease is found mainly in children under 5 and in young adults. In developing countries, children under 2 are most affected. It is also a frequent cause of traveller's diarrhoea.

Scope of the Problem

Approximately 5%-14% of all diarrhoea worldwide is thought to be caused by Campylobacter.

Interventions

Prevention requires:

• Safe drinking-water supply including continuous disinfection (chlorination) of drinking-water;
• proper handling of production animals;
• proper sewage-disposal systems and protection of the water supply from contamination;
• thorough cooking of potentially contaminated foods;
• adequate personal hygiene (washing hands after toilet use as well as after handling pets or farm animals);
• avoiding raw milk.

Treatment includes:

• rehydration therapy plus antibiotic therapy for those with severe infection.

Cholera

Cholera outbreaks can occur sporadically in any part of the world where water supplies, sanitation, food safety and hygiene practices are inadequate. Overcrowded communities with poor sanitation and unsafe drinking-water supplies are most frequently affected.

The disease and how it affects people

Cholera is an acute infection of the intestine, which begins suddenly with painless watery diarrhoea, nausea and vomiting. Most people who become infected have very mild diarrhoea or symptom-free infection. Malnourished people in particular experience more severe symptoms. Severe cholera cases present with profuse diarrhoea and vomiting. Severe, untreated cholera can lead to rapid dehydration and death. If untreated, 50% of people with severe cholera will die, but prompt and adequate treatment reduces this to less than 1% of cases.

The cause

Cholera is caused by the bacterium Vibrio cholerae. People become infected after eating food or drinking water that has been contaminated by the faeces of infected persons. Raw or undercooked seafood may be a source of infection in areas where cholera is prevalent and sanitation is poor. Vegetables and fruit that have been washed with water contaminated by sewage may also transmit the infection if V. cholerae is present.

Distribution

Cholera cases and deaths were officially reported to WHO, in the year 2000, from 27 countries in Africa, 9 countries in Latin America, 13 countries in Asia, 2 countries in Europe, and 4 countries in Oceania.

Scope of the Problem

Control of cholera is a major problem in several Asian countries as well as in Africa. In the year 2000, some 140,000 cases resulting in approximately 5000 deaths were officially notified to WHO. Africa accounted for 87% of these cases. After almost a century of no reported cases of the disease, cholera reached Latin America in 1991; however, the number of cases reported has been steadily declining since 1995.

Interventions

To prevent the spread of cholera, the following four interventions are essential:

• Provision of adequate safe drinking-water
• Proper personal hygiene
• Proper food hygiene
• Hygienic disposal of human excreta.

Treatment of cholera consists mainly in replacement of lost fluids and salts. The use of oral rehydration salts (ORS) is the quickest and most efficient way of doing this. Most people recover in 3 to 6 days. If the infected person becomes severely dehydrated, intravenous fluids can be given. Antibiotics are not necessary to successfully treat a cholera patient.

Cyanobacterial Toxins

Cyanobacteria or blue-green algae occur worldwide especially in calm, nutrient-rich waters. Some species of cyanobacteria produce toxins that affect animals and humans. People may be exposed to cyanobacterial toxins by drinking or bathing in contaminated water. The most frequent and serious health effects are caused by drinking water containing the toxins (cyanobacteria), or by ingestion during recreational water contact.

The disease and how it affects people

Disease due to cyanobacterial toxins varies according to the type of toxin and the type of water or water-related exposure (drinking, skin contact, etc.). Humans are affected with a range of symptoms including skin irritation, stomach cramps, vomiting, nausea, diarrhoea, fever, sore throat, headache, muscle and joint pain, blisters of the mouth and liver damage. Swimmers in water containing cyanobacterial toxins may suffer allergic reactions, such as asthma, eye irritation, rashes, and blisters around the mouth and nose. Animals, birds, and fish can also be poisoned by high levels of toxin-producing cyanobacteria.

The cause

Cyanobacteria are also known as blue-green algae, so named because these organisms have characteristics of both algae and bacteria, although they are now classified as bacteria. The blue-green colour comes from their ability to photosynthesize, like plants.

Cyanobacterial toxins are classified by how they affect the human body. Hepatotoxins (which affect the liver) are produced by some strains of the cyanobacteria Microcystis, Anabaena, Oscillatoria, Nodularia, Nostoc, Cylindrospermopsis and Umezakia. Neurotoxins (which affect the nervous system) are produced by some strains of Aphanizomenon and Oscilatoria. Cyanobacteria from the species Cylindroapermopsis raciborski may also produce toxic alkaloids, causing gastrointestinal symptoms or kidney disease in humans. Not all cyanobacteria of these species form toxins and it is likely that there are as yet unrecognized toxins.

People are mainly exposed to cyanobacterial toxins by drinking or bathing in contaminated water. Other sources include algal food tablets. Some species form a scum on the water, but high concentrations may also be present throughout the affected water. Surface scums, where they occur, represent a specific hazard to human health because of their particularly high toxin contact. Contact, especially by children, should be avoided.

Distribution

The organisms can grow rapidly in favourable conditions, such as calm nutrient-rich fresh or marine waters in warm climates or during the late summer months in cooler parts of the world. Blooms of cyanobacteria tend to occur repeatedly in the same water, posing a risk of repeated exposure to some human populations. Cyanobacterial toxins in lakes, ponds, and dugouts in various parts of the world have long been known to cause poisoning in animals and humans; one of the earliest reports of their toxic effects was in China 1000 years ago (Chorus and Bartram, 1999).

Scope of the Problem

Cyanobacteria have been linked to illness in various regions throughout the world, including North and South America, Africa, Australia, Europe, Scandinavia and China. There are no reliable figures for the number of people affected worldwide. The only documented and scientifically substantiated human deaths due to cyanobacterial toxins have been due to exposure during dialysis. People exposed through drinking-water and recreational-water have required intensive hospital care.

Interventions

1.       Reducing nutrient build-up (eutrophication) in lakes and reservoirs, especially by better management of wastewater disposal systems and control of pollution by fertilizers (including manure) from agriculture.

2.       Educating the staff in the health and water supply sectors, as well as the public, about the risks of drinking, bathing or water sports in water likely to contain high densities of cyanobacteria.

3.       Water treatment to remove the organisms and their toxins from drinking-water supplies, where appropriate.

References

Toxic Cyanobacteria in Water: a guide to their public health consequences, monitoring and management, edited by J. Bartram& I. Chorus. Geneva, World Health Organization, 1999.

Dengue and Dengue Haemorrhagic Fever

The disease and how it affects people

Dengue is a mosquito-borne infection which in recent years has become a major international public health concern. Dengue fever is a severe, flu-like illness that affects infants, young children and adults but rarely causes death. Dengue haemorrhagic fever (DHF) is a potentially lethal complication and is today a leading cause of childhood death in several Asian countries.

The clinical features of dengue fever vary according to the age of the patient. Infants and young children may have a feverish illness with rash. Older children and adults may have either a mild feverish illness, or the classical incapacitating disease with abrupt onset and high fever, severe headache, pain behind the eyes, muscle and joint pains, and rash. The rash may not be visible in dark-skinned people. DHF is a potentially deadly complication that is characterized by high fever, haemorrhage - often with enlargement of the liver—and in the most severe cases, circulatory failure. The illness commonly begins with a sudden rise in temperature accompanied by facial flushing and other general symptoms of dengue fever. The fever usually continues for 2-7 days. It can be as high as 40-41° C, and may be accompanied by febrile convulsions.

The cause

There are four distinct, but closely related, viruses which cause dengue. Recovery from infection by one provides lifelong immunity against re-infection with that type, but confers only partial and transient protection against subsequent infection by any of the other three types. Indeed, there is good evidence that sequential infection with different types increases the risk of the more serious disease known as dengue haemorrhagic fever (DHF). Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitos. Mosquitos generally acquire the virus while feeding on the blood of infected people during the time the virus is circulating in their bloodstream. This is approximately the same time as they are experiencing fever. Once infected, a mosquito is capable of transmitting the virus to susceptible people for the rest of its life. Infected female mosquitos may also transmit the virus to the next generation of mosquitos.

Distribution

The global prevalence of dengue has grown dramatically in recent decades. Dengue is found in tropical and subtropical regions around the world, predominately in urban and periurban areas, where Aedes mosquitos are prevalent. The disease is now found in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South and South-East Asia, and the Western Pacific. It is typically a disease of urbanized areas, where the mosquitoes find breeding opportunities in small water collections in and around houses: drinking water containers, discarded car tyres, flower vases and ant traps are well-known breeding places.

Scope of the Problem

Globally there are an estimated 50-100 million cases of dengue fever and around 500 000 cases of DHF each year.

Interventions

At present , there is no vaccine to protect against dengue. The most effective method of prevention is to eliminate the mosquito that causes the disease. This requires removal of the mosquito breeding-sites, known as source reduction. Proper disposal of solid waste helps to reduce the collection of water in discarded articles. Other control measures include preventing mosquito bites with screens, protective clothing and insect repellents; in epidemic risk areas, application of insecticide is practiced (through an application method known as fogging) to decrease the mosquito population.

Prepared for World Water Day 2001. Reviewed by staff and experts from the cluster on Communicable Diseases (CDS) and the Water, Sanitation and Health unit (WSH), World Health Organization (WHO).

Diarrhoea

Diarrhoea occurs world-wide and causes 4% of all deaths and 5% of health loss to disability. It is most commonly caused by gastrointestinal infections which kill around 2.2 million people globally each year, mostly children in developing countries. The use of water in hygiene is an important preventive measure but contaminated water is also an important cause of diarrhoea. Cholera and dysentery cause severe, sometimes life threatening forms of diarrhoea.

The disease and how it affects people

Diarrhoea is the passage of loose or liquid stools more frequently than is normal for the individual. It is primarily a symptom of gastrointestinal infection. Depending on the type of infection, the diarrhoea may be watery (for example in cholera) or passed with blood (in dysentery for example).

Diarrhoea due to infection may last a few days, or several weeks, as in persistent diarrhoea. Severe diarrhoea may be life threatening due to fluid loss in watery diarrhoea, particularly in infants and young children, the malnourished and people with impaired immunity.

The impact of repeated or persistent diarrhoea on nutrition and the effect of malnutrition on susceptibility to infectious diarrhoea can be linked in a vicious cycle amongst children, especially in developing countries.

Diarrhoea is also associated with other infections such as malaria and measles. Chemical irritation of the gut or non-infectious bowel disease can also result in diarrhoea.

The cause

Diarrhoea is a symptom of infection caused by a host of bacterial, viral and parasitic organisms most of which can be spread by contaminated water. It is more common when there is a shortage of clean water for drinking, cooking and cleaning and basic hygiene is important in prevention.

Water contaminated with human faeces for example from municipal sewage, septic tanks and latrines is of special concern. Animal faeces also contain microorganisms that can cause diarrhoea.

Diarrhoea can also spread from person to person, aggravated by poor personal hygiene. Food is another major cause of diarrhoea when it is prepared or stored in unhygienic conditions. Water can contaminate food during irrigation, and fish and seafood from polluted water may also contribute to the disease.

Distribution

The infectious agents that cause diarrhoea are present or are sporadically introduced throughout the world. Diarrhoea is a rare occurrence for most people who live in developed countries where sanitation is widely available, access to safe water is high and personal and domestic hygiene is relatively good. World-wide around 1.1 billion people lack access to improved water sources and 2.4 billion have no basic sanitation. Diarrhoea due to infection is widespread throughout the developing world. In Southeast Asia and Africa, diarrhoea is responsible for as much as 8.5% and 7.7% of all deaths respectively.

Scope of the Problem

Amongst the poor and especially in developing countries, diarrhoea is a major killer. In 1998, diarrhoea was estimated to have killed 2.2 million people, most of whom were under 5 years of age (WHO, 2000). Each year there are approximately 4 billion cases of diarrhoea worldwide.

Interventions

Key measures to reduce the number of cases of diarrhoea include:

• Access to safe drinking water.
• Improved sanitation.
• Good personal and food hygiene.
• Health education about how infections spread.

Key measures to treat diarrhoea include:

• Giving more fluids than usual, including oral rehydration salts solution, to prevent dehydration.
• Continue feeding.
• Consulting a health worker if there are signs of dehydration or other problems.

References

WHO(2000) Global Water Supply and Sanitation Assessment. World Health Organization. Geneva

The World Health Report 2000, World Health Organization (WHO), Geneva

Prepared for World Water Day. Reviewed by staff and experts in Family and Community Health Unit (FCH), and the Water, Sanitation and Health Unit (WSH), World Health Organization (WHO), Geneva.

Fluorosis

The disease and how it affects people

Ingestion of excess fluoride, most commonly in drinking-water, can cause fluorosis which affects the teeth and bones. Moderate amounts lead to dental effects, but long-term ingestion of large amounts can lead to potentially severe skeletal problems. Paradoxically, low levels of fluoride intake help to prevent dental caries. The control of drinking-water quality is therefore critical in preventing fluorosis. The condition and its effect on people Fluorosis is caused by excessive intake of fluoride. The dental effects of fluorosis develop much earlier than the skeletal effects in people exposed to large amounts of fluoride. Clinical dental fluorosis is characterized by staining and pitting of the teeth. In more severe cases all the enamel may be damaged. However, fluoride may not be the only cause of dental enamel defects. Enamel opacities similar to dental fluorosis are associated with other conditions, such as malnutrition with deficiency of vitamins D and A or a low protein-energy diet. Ingestion of fluoride after six years of age will not cause dental fluorosis.

Chronic high-level exposure to fluoride can lead to skeletal fluorosis. In skeletal fluorosis, fluoride accumulates in the bone progressively over many years. The early symptoms of skeletal fluorosis, include stiffness and pain in the joints. In severe cases, the bone structure may change and ligaments may calcify, with resulting impairment of muscles and pain.

Acute high-level exposure to fluoride causes immediate effects of abdominal pain, excessive saliva, nausea and vomiting. Seizures and muscle spasms may also occur.

The cause

Acute high-level exposure to fluoride is rare and usually due to accidental contamination of drinking-water or due to fires or explosions. Moderate-level chronic exposure (above 1.5 mg/litre of water - the WHO guideline value for fluoride in water) is more common. People affected by fluorosis are often exposed to multiple sources of fluoride, such as in food, water, air (due to gaseous industrial waste), and excessive use of toothpaste. However, drinking water is typically the most significant source. A person's diet, general state of health as well as the body's ability to dispose of fluoride all affect how the exposure to fluoride manifests itself.

Distribution

Fluoride in water is mostly of geological origin. Waters with high levels of fluoride content are mostly found at the foot of high mountains and in areas where the sea has made geological deposits. Known fluoride belts on land include: one that stretches from Syria through Jordan, Egypt, Libya, Algeria, Sudan and Kenya, and another that stretches from Turkey through Iraq, Iran, Afghanistan, India, northern Thailand and China. There are similar belts in the Americas and Japan. In these areas fluorosis has been reported.

Scope of the Problem

The prevalence of dental and skeletal fluorosis is not entirely clear. It is believed that fluorosis affects millions of people around the world, but as regards dental fluorosis the very mild or mild forms are the most frequent.

Interventions

Removal of excessive fluoride from drinking-water is difficult and expensive. The preferred option is to find a supply of safe drinking-water with safe fluoride levels. Where access to safe water is already limited, de-fluoridation may be the only solution. Methods include: use of bone charcoal, contact precipitation, use of Nalgonda or activated alumina (Nalgonda is called after the town in South India, near Hyderabad, where the aluminium sulfate-based defluoridation was first set up at a water works level). Since all methods produce a sludge with very high concentration of fluoride that has to be disposed of, only water for drinking and cooking purposes should be treated, particularly in the developing countries.

Health education regarding appropriate use of fluorides.

Mothers in affected areas should be encouraged to breastfeed since breast milk is usually low in fluoride.

References

World Health Organization. Guidelines for drinking-water quality. Vol. 1. Geneva, 1993 (Second edition)

World Health Organization. Guidelines for drinking-water quality. Vol. 2. Geneva, 1999 (Second edition)

Fluoride in drinking-water, WHO/IWA (in preparation)

Guinea-Worm Disease (Dracunculiasis)

The disease and how it affects people

Guinea worm disease is a debilitating and painful infection caused by a large nematode (roundworm), Dracunculus medinensis. It begins with a blister, usually on the leg. Around the time of its eruption, the person may experience itching, fever, swelling and burning sensations. Infected persons try to relieve the pain by immersing the infected part in water, usually open water sources such as ponds and shallow wells. This stimulates the worm to emerge and release thousands of larvae into the water. The larva is ingested by a water flea (cyclops), where it develops and becomes infective in two weeks. When a person drinks the water, the cyclops is dissolved by the acidity of the stomach, and the larva is activated and penetrates the gut wall. It develops and migrates through the subcutaneous tissue. After about one year, a blister forms and the mature worm, 1m long, tries to emerge, thus repeating the life cycle.

For persons living in remote areas with no access to medical care, healing of the ulcers can take several weeks. This can be further complicated by bacterial infection, stiff joints, arthritis and even permanent debilitating contractures of the limbs. People in endemic villages are incapacitated during peak agricultural activities. This can seriously affect their agricultural production and the availability of food in the household, and consequently the nutritional status of their family members, particularly young children.

Distribution

At the beginning of the 20th century, guinea-worm disease, was widespread in many countries in Africa and Asia. It is estimated that there were about 50 million cases in the 1950s. Due to concentrated efforts by the international community and the endemic countries, the number of cases of guinea-worm disease was reduced to about 96 000 by 1999. Guinea-worm disease is prevalent in only 13 countries in Africa including Sudan, Nigeria, Ghana, Burkina Faso, Niger, Togo and Côte d'Ivoire. A small number of cases have also been reported in Uganda, Benin, Mali, Mauritania, Ethiopia and Chad.

Scope of the Problem

Humans are the only known reservoirs for guinea-worm disease, and infection is through the use of contaminated water in remote rural areas of African countries. About two-thirds of the cases (66 000) reported in 1999 were from Sudan, where the continuing civil war is hampering efforts to eradicate the disease.

Interventions

Provision of safe drinking-water in rural and isolated areas is the pillar intervention to eliminate the disease. The disease disappeared from many countries such as from the Islamic Republic of Iran and Saudi Arabia due to improvement in water supply. In 1991, the World Health Assembly adopted a resolution to eradicate the disease.

Dracunculiasis Eradication Programme

WHO has promoted the eradication campaign, which focuses on: interruption of transmission of the disease; surveillance of new cases; and certification of eradication. Specific interventions include: health education, case containment, community-based surveillance systems, provision of safe water, including use of filtering devices and chemical treatment of water sources.

Prepared for World Water Day 2001. Reviewed by staff and experts from the cluster on Communicable Diseases (CDS), and Water, Sanitation and Health unit (WSH), World Health Organization (WHO).

Hepatitis

Hepatitis, a broad term for inflammation of the liver, has a number of infectious and non-infectious causes. Two of the viruses that cause hepatitis (hepatitis A and E) can be transmitted through water and food; hygiene is therefore important in their control.

The disease and how it affects people

Among the infectious causes, hepatitis A and hepatitis E are associated with inadequate water supplies and poor sanitation and hygiene, leading to infection and inflammation of the liver. The illness starts with an abrupt onset of fever, body weakness, loss of appetite, nausea and abdominal discomfort, followed by jaundice within a few days. The disease may range from mild (lasting 1-2 weeks) to severe disabling disease (lasting several months). In areas highly endemic for hepatitis A, most infections occur during early childhood. The majority of cases may not show any symptoms; fatal cases due to fulminant acute hepatitis are rare. Nearly all patients recover completely with no long-term effects.

The cause

Hepatitis A and E viruses, while unrelated to one another, are both transmitted via the faecal-oral route, most often through contaminated water and from person to person. Hepatitis A could also be transmitted via food contaminated by infected food-handlers, uncooked foods, or foods handled after cooking. Hepatitis A has also caused outbreaks transmitted through injecting or non-injecting drug use.

Distribution

Both hepatitis A and E are found worldwide. Hepatitis A is particularly frequent in countries with poor sanitary and hygienic conditions (in Africa, Asia, and Central and South America). Countries with economies in transition and some regions of industrialized countries where sanitary conditions are sub-standard are also highly affected, e.g.in southern and eastern Europe and some parts of the Middle East. Outbreaks of hepatitis E have occurred in Algeria, Bangladesh, China, Ethiopia, Indonesia, Iran, Libyan Arab Jamahiriya, Mexico, Myanmar, Nepal, Pakistan, Somalia, and the Central Asian republics of the CIS.

Scope of the Problem

The mortality rate is low (0.2% of icteric cases) and the disease ultimately resolves. Occasionally, extensive necrosis of the liver occurs during the first 6-8 weeks of illness. In such cases, high fever, marked abdominal pain, vomiting, jaundice, and hepatic encephalopathy (with coma and seizures) are the signs of fulminant hepatitis, leading to death in 70-90% of the patients. In these cases mortality is highly correlated with increasing age, and survival is uncommon over 50 years of age. Among patients with chronic hepatitis B or C or underlying liver disease, who are superinfected with hepatitis A virus, the mortality rate increases considerably.

Improved economic and sanitary conditions may lead to a higher disease incidence in older age groups, with higher reported rates of clinically evident hepatitis A. In countries with very low hepatitis A infection rates, the disease may occur among specific risk groups such as travellers. Hepatitis E is mainly found in young to middle-aged adults. Women in the third trimester of pregnancy are especially susceptible to acute fulminant hepatitis arising from hepatitis E infection.

Interventions

As there are no specific antiviral drugs against hepatitis A and E, prevention of these viral diseases remains the most important weapon for their control, such as:

• Providing education on good sanitation and personal hygiene, especially hand-washing
• Adequate and clean water supplies and proper waste disposal
• Vaccination against hepatitis A for persons at risk, e.g. travellers visiting areas where the disease is common.

Prepared for World Water Day 2001. Reviewed by staff and experts from the cluster on Communicable Diseases (CDS) and the Water, Sanitation and Health unit (WSH), World Health Organization (WHO).

Japanese Encephalitis

Japanese encephalitis is a viral disease that infects animals and humans. It is transmitted by mosquitoes and in humans causes inflammation of the membranes around the brain. Intensification and expansion of irrigated rice production systems in South and South-East Asia over the past 20 years have had an important impact on the disease burden caused by Japanese encephalitis. Where irrigation expands into semi-arid areas, the flooding of the fields at the start of each cropping cycle leads to an explosive build-up of the mosquito population. This may cause the circulation of the virus to spill over from their usual hosts (birds and pigs) into the human population.

The disease and how it affects people

Japanese encephalitis (JE) is a disease caused by a flavivirus that affects the membranes around the brain. Most JE virus infections are mild (fever and headache) or without apparent symptoms, but approximately 1 in 200 infections results in severe disease characterized by rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and death. The case fatality rate can be as high as 60% among those with disease symptoms; 30% of those who survive suffer from lasting damage to the central nervous system. In areas where the JE virus is common, encephalitis occurs mainly in young children because older children and adults have already been infected and are immune.

The cause

The virus causing Japanese encephalitis is transmitted by mosquitoes belonging to the Culex tritaeniorhynchus and Culex vishnui groups, which breed particularly in flooded rice fields. The virus circulates in ardeid birds (herons and egrets). Pigs are amplifying hosts, in that the virus reproduces in pigs and infects mosquitoes that take blood meals, but does not cause disease. The virus tends to spill over into human populations when infected mosquito populations build up explosively and the human biting rate increases (these culicines are normally zoophilic, i.e. they prefer to take blood meals from animals).

Distribution

Japanese encephalitis is a leading cause of viral encephalitis in Asia with 30,000-50,000 clinical cases reported annually. It occurs from the islands of the Western Pacific in the east to the Pakistani border in the west, and from Korea in the north to Papua New Guinea in the south. Because of the critical role of pigs, its presence in Muslim countries is negligible. JE distribution is very significantly linked to irrigated rice production combined with pig rearing.

Scope of the Problem

Japanese encephalitis is a patchy disease and important outbreaks have occurred in a number of places in the past 15 years, including South India (Arkot district in Tamil Nadu) and in Sri Lanka (Mahaweli System H).

Interventions

An effective killed vaccine is available for Japanese encephalitis, but it is expensive and requires one primary vaccination followed by two boosters. This is an adequate intervention for travellers, but has limited public health value in areas where health services have limited resources. An inexpensive live-attenuated vaccine is used in China, but is not available elsewhere. Chemical vector control is not a solution, as the breeding sites (irrigated rice fields) are extensive. In some rice production systems faced with water shortages, however, certain water management measures (alternate wetting and drying) may be applied that reduce vector populations. Personal protection (using repellents and/or mosquito nets) will be effective under certain conditions. Eliminating the pig population is often a measure taken in the wake of outbreaks. Certainly, the introduction of pig rearing as a secondary source of income for rice-growing farmers in receptive areas must never be encouraged.

Prepared for World Water Day 2001. Reviewed by staff and experts from the cluster on Communicable Diseases (CDS), and the Water, Sanitation and Health Unit (WSH), World Health Organization (WHO), Geneva.

Lead poisoning

Exposure to lead causes a variety of health effects, and affects children in particular. Water is rarely an important source of lead exposure except where lead pipes, for instance in old buildings, are common. Removal of old pipes is costly but the most effective measure to reduce lead exposure from water.

The disease and how it affects people

Lead is a metal with no known biological benefit to humans. Too much lead can damage various systems of the body including the nervous and reproductive systems and the kidneys, and it can cause high blood pressure and anemia. Lead accumulates in the bones and lead poisoning may be diagnosed from a blue line around the gums. Lead is especially harmful to the developing brains of fetuses and young children and to pregnant women. Lead interferes with the metabolism of calcium and Vitamin D. High blood lead levels in children can cause consequences which may be irreversible including learning disabilities, behavioral problems, and mental retardation. At very high levels, lead can cause convulsions, coma and death.

The cause

People are exposed to lead through the air they breathe, through water and through food/ingestion. Toxic effects are usually due to long term exposure. The population groups at greatest risk of exposure are young children and workers. A recent report suggests that even a blood level of 10 micrograms per decilitre can have harmful effects on children's learning and behavior (CDC, 2000). People can be exposed to lead contamination from the motor vehicle exhaust of leaded gasoline, as well as from industrial sources such as smelters and lead manufacturing and recycling industries, from cottage industry uses and waste sites (e.g. contaminated landfills).

Exposure to lead through water is generally low in comparison with exposure through air or food. Lead from natural sources is present in tap water to some extent, but analysis of both surface and ground water suggests that lead concentration is fairly low. The main source of lead in drinking water is (old) lead piping and lead-combining solders. Removing old piping is costly and lead continues to dissolve even from old pipes. The amount of lead that may dissolve in water depends on acidity (pH), temperature, water hardness and standing time of the water. Secondary pollution from industry can contaminate water through the effluents produced.

Other sources include use of lead-containing ceramics for cooking, eating or drinking. In some countries, people are exposed to lead after eating food products from cans that contain lead solder in the seams of the cans. Very small children are especially at risk to exposure, for example through the ingestion of paint chips from lead-based paint.

Scope of the Problem

The major sources of lead vary according to the region and include: industrial use of lead, lead recycling, leaded gasoline and lead piping used in water distribution systems. Lead in the environment is distributed mostly by air but there is some discharge into soil and water. Water is not normally considered the major source of pollution exposure to lead. In individual households with lead piping and soft waters it may be important. As other sources of exposure to lead are increasingly controlled, water attracts increasing attention.

Interventions

Preventive measures include :

• Environmental standards that remove lead from petrol/gasoline, paint and plumbing.
• If lead pipes cannot be removed, water (cold should be flushed through in the morning before drinking).
• Enforcement of occupational health standards.
• Surveillance of potentially exposed population groups, especially the vulnerable ones (small children, pregnant women, workers).
• Water treatment.
• Removing lead solder from food cans.
• Use of lead-free paint in homes.
• Screening of children for blood levels over acceptable limit and referral for medical care as necessary.

The health based guideline for lead in drinking water is 0.1 milligrams per litre (WHO, 1993). If high levels are detected in a supply, alternative supplies or bottled water maybe necessary to protect young children.

References

CDC Childhood Lead Poisoning Prevention Program

Leptospirosis

The disease and how it affects people

Leptospirosis is a bacterial disease that affects both humans and animals. The early stages of the disease may include high fever, severe headache, muscle pain, chills, redness in the eyes, abdominal pain, jaundice, haemorrhages in skin and mucous membranes (including pulmonary bleeding), vomiting, diarrhoea and a rash.

The cause

Pathogenic Leptospira spp. cause leptospirosis. Human infection occurs through direct contact with the urine of infected animals or by contact with a urine-contaminated environment, such as surface water, soil and plants. The causative organisms have been found in a variety of both wild and domestic animals, including rodents, insectivores, dogs, cattle, pigs and horses. Leptospires can gain entry through cuts and abrasions in the skin and through mucous membranes of the eyes, nose and mouth. Human-to-human transmission occurs only rarely.

Distribution

Leptospirosis occurs worldwide, in both rural and urban areas and in temperate and tropical climates. It is an occupational hazard for people who work outdoors or with animals, such as rice and sugar-cane field workers, farmers, sewer workers, veterinarians, dairy workers and military personnel. It is also a recreational hazard to those who swim or wade in contaminated waters. In endemic areas the number of leptospirosis cases may peak during the rainy season and even may reach epidemic proportions in case of flooding.

Scope of the Problem

The number of human cases worldwide is not well-documented. It probably ranges from 0.1 to 1 per 100 000 per year in temperate climates to 10 or more per 100 000 per year in the humid tropics. During outbreaks and in high-risk groups, 100 or more per 100 000 may be infected. For several reasons leptospirosis is overlooked and consequently underreported in many areas of the world. In the wake of hurricane Mitch in 1995, an outbreak of leptospirosis with pulmonary haemorrhages was reported in Nicaragua. In 1998, there was an outbreak in the continental United States. 1998 also saw an outbreak in Peru and Ecuador following heavy flooding. A post-cyclone outbreak was reported in Orissa, India in 1999.

Interventions

The disease is often difficult to diagnose clinically; laboratory support is indispensable. Treatment with appropriate antibiotics should be initiated as early as possible. Untreated cases can progress to a more severe and potentially fatal stage. Preventive measures must be based on a knowledge of the groups at particular risk of infection and the relevant local epidemiological factors. For intervention one may:

a.       aim at control at the level of the infection source (e.g. rodent control, animal vaccination);

b.       interrupt the transmission route (e.g. wearing protective clothing, refrain from contact with infected animals and from swimming in contaminated water, provide clean drinking-water); or

c.       prevent infection or disease in the human host (e.g. vaccination, antibiotic prophylaxis, information to doctors, veterinarians, risk groups and the general population).

Malaria

Malaria, the world's most important parasitic infectious disease, is transmitted by mosquitoes which breed in fresh or occasionally brackish water.

The disease and how it affects people

The symptoms of malaria include fever, chills, headache, muscle aches, tiredness, nausea and vomiting, diarrhoea, anaemia, and jaundice (yellow colouring of the skin and eyes). Convulsions, coma, severe anaemia and kidney failure can also occur. The severity and range of symptoms depend on the specific type of malaria. In certain types, the infection can remain inactive for up to five years and then recur. In areas with intense malaria transmission, people can develop protective immunity after repeated infections. Without prompt and effective treatment, malaria can evolve into a severe cerebral form followed by death. Malaria is among the five leading causes of death in under-5-year-old children in Africa.

The cause

Malaria is caused by four species of Plasmodium parasites (P. falciparum, P. vivax, P. ovale, P. malariae). People get malaria after being bitten by a malaria-infected Anopheles mosquito. Some female mosquitoes take their blood-meal at dusk and early evening, but others bite during the night or in the early hours of the morning. When a mosquito bites an infected person, it ingests malaria parasites with the blood. During a period of 8 to 35 days (depending on the ambient temperature), the parasite develops in the mosquito. The infective form (sporozoite) ends up in the salivary glands and is injected into the new human host at subsequent blood-meals. In the human host, the sporozoites migrate to the liver, multiply inside liver cells, and spread into the bloodstream. The liver phase can last between 8 days and several months, depending on the malaria species. Their growth and multiplication takes place inside red blood cells. Clinical symptoms occur when the red blood cells break up. If this happens in large numbers, the person experiences the characteristic intermittent fevers of the disease. The released parasites invade other blood cells. Most people begin feeling sick 10 days to 4 weeks after being infected.

Distribution

Today, malaria occurs mostly in tropical and subtropical countries, particularly in Africa south of the Sahara, South-East Asia, and the forest fringe zones in South America. The ecology of the disease is closely associated with the availability of water, as the larval stage of mosquitoes develops in different kinds of water bodies. The mosquito species vary considerably in their water-ecological requirements, (sun-lit or shaded, with or without aquatic vegetation, stagnant or slowly streaming, fresh or brackish) and this affects the disease ecology. Climate change (global warming) appears to be moving the altitude limits of malaria to higher elevations, for example in the East African highlands and Madagascar.

The construction of irrigation systems and reservoirs in some parts of the world can have a dramatic impact on malaria distribution and on the intensity of its transmission.

Scope of the Problem

WHO estimates 300-500 million cases of malaria, with over one million deaths each year.

The main burden of malaria (more than 90%) is in Africa south of the Sahara with an estimated annual number of deaths over 1 million. Two thirds of the remaining burden hits six countries: Brazil, Colombia, India, Solomon Islands, Sri Lanka and Viet Nam. In many parts the natural habitat sustains intense malaria transmission; in others, water resources development (irrigation, dams, urban water supply) has exacerbated the transmission intensity and caused the distribution of the disease to spread. In yet others, for example the Central Asian republics of the CIS, malaria has returned as a result of a breakdown in water management and maintenance problems of local irrigation systems.

Interventions

WHO's Strategy for Malaria Control, which forms the basis of the Roll Back Malaria initiative, identifies four main interventions:

1.       Reducing mortality, particularly among children, by early case-detection and prompt treatment with effective anti-malarial drugs

2.       Promoting the use of insecticide-treated bed nets, especially by children and pregnant women

3.       Prevention of malaria in pregnancy by applying intermittent preventive therapy

4.       Ensuring early detection and control of malaria epidemics, especially in emergency situations.

Where appropriate, countries and communities are being encouraged to reduce mosquito breeding sites by filling in and draining water bodies and through other environmental management schemes.

Malnutrition

Malnutrition is a major health problem, especially in developing countries. Water supply, sanitation and hygiene, given their direct impact on infectious disease, especially diarrhoea, are important for preventing malnutrition. Both malnutrition and inadequate water supply and sanitation are linked to poverty. The impact of repeated or persistent diarrhoea on nutrition-related poverty and the effect of malnutrition on susceptibility to infectious diarrhoea are reinforcing elements of the same vicious circle, especially amongst children in developing countries.

The disease and how it affects people

Malnutrition essentially means “bad nourishment”. It concerns not enough as well as too much food, the wrong types of food, and the body's response to a wide range of infections that result in malabsorption of nutrients or the inability to use nutrients properly to maintain health. Clinically, malnutrition is characterized by inadequate or excess intake of protein, energy, and micronutrients such as vitamins, and the frequent infections and disorders that result.

People are malnourished if they are unable to utilize fully the food they eat, for example due to diarrhoea or other illnesses (secondary malnutrition), if they consume too many calories (overnutrition), or if their diet does not provide adequate calories and protein for growth and maintenance (undernutrition or protein-energy malnutrition).

Malnutrition in all its forms increases the risk of disease and early death. Protein-energy malnutrition, for example, plays a major role in half of all under-five deaths each year in developing countries (WHO 2000). Severe forms of malnutrition include marasmus (chronic wasting of fat, muscle and other tissues); cretinism and irreversible brain damage due to iodine deficiency; and blindness and increased risk of infection and death from vitamin A deficiency.

Nutritional status is compromised where people are exposed to high levels of infection due to unsafe and insufficient water supply and inadequate sanitation. In secondary malnutrition, people suffering from diarrhoea will not benefit fully from food because frequent stools prevents adequate absorption of nutrients. Moreover, those who are already experiencing protein-energy malnutrition are more susceptible to, and less able to recover from, infectious diseases.

The cause

Individual nutritional status depends on the interaction between food that is eaten, the overall state of health and the physical environment. Malnutrition is both a medical and a social disorder, often rooted in poverty. Combined with poverty, malnutrition contributes to a downward spiral that is fuelled by an increased burden of disease, stunted development and reduced ability to work. Poor water and sanitation are important determinants in this connection, but sometimes improvements do not benefit the entire population, for example where only the wealthy can afford better drinking-water supplies or where irrigation is used to produce export crops. Civil conflicts and wars, by damaging water infrastructure and contaminating supplies, contribute to increased malnutrition.

Scope of the Problem

Chronic food deficits affect about 792 million people in the world (FAO 2000), including 20% of the population in developing countries. Worldwide, malnutrition affects one in three people and each of its major forms dwarfs most other diseases globally (WHO, 2000). Malnutrition affects all age groups, but it is especially common among the poor and those with inadequate access to health education and to clean water and good sanitation. More than 70% of children with protein-energy malnutrition live in Asia, 26% live in Africa, and 4% in Latin America and the Caribbean (WHO 2000).

Interventions

Interventions that contribute to preventing malnutrition include :

• Improved water supply, sanitation and hygiene.
• Health education for a healthy diet.
• Improved access, by the poor, to adequate amounts of healthy food.
• Ensuring that industrial and agricultural development do not result in increased malnutrition.

References

WHO. Turning the tide of malnutrition: responding to the challenge of the 21st century. Geneva: WHO, 2000 (WHO/NHD/00.7)

Methaemoglobinemia

Methaemoglobinaemia caused by the decreased ability of blood to carry vital oxygen around the body. One of the most common causes is nitrate in drinking water. It is most important in bottle fed infants and water from wells in rural areas is of special concern. Controlling nitrate levels in drinking water sources to below around 50mg/litre is an effective preventive measure.

The disease and how it affects people

Methaemoglobinemia is characterized by reduced ability of the blood to carry oxygen because of reduced levels of normal haemoglobin. It is uncommon. Infants are most often affected, and may seem healthy, but show signs of blueness around the mouth, hands, and feet, hence the common name “blue baby syndrome”. These children may also have trouble breathing as well as vomiting and diarrhoea. In extreme cases, there is marked lethargy, an increase in the production of saliva, loss of consciousness and seizures. Some cases may be fatal.

In the body nitrates are converted to nitrites. The nitrites react with haemoglobin in the red blood cells to form methaemoglobin, affecting the blood's ability to carry enough oxygen to the cells of the body. Bottle-fed infants less than three months of age are particularly at risk. The heamoglobin of infants is more susceptible and the condition is made worse by gastrointestinal infection. Older people may also be at risk because of decreased gastric acid secretion.

Malnutrition and infection seem to increase the risk of methaemoglobinaemia (McDonald and Kay, 1988). The general health of the infant as well as Vitamin C intake may determine whether or not the condition develops (Super et al, 1981).

Others at risk for developing methaemoglobinaemia include: adults with a hereditary predisposition, people with peptic ulcers or chronic gastritis, as well as dialysis patients.

The cause

The most common cause of methaemoglobinemia is high levels of nitrates in drinking-water. High nitrate levels may be present in drinking-water due to the use of manure and fertilizers on agricultural land. The natural level of nitrites and nitrates from the environment is normally a few milligrams per litre, although high levels may occur naturally in some areas. Intense farming practice may increase this to more than 50 mg/litre (WHO 1998). Levels greater than 50mg/litre are known to have been associated with methaemoglobinaemia in bottle fed infants. Nitrate is also found in vegetables. Methaemoglobinaemia can also be a side effect of some drugs (phenacetin and sulphonamides), although this is very rare with modern drugs.

Scope of the Problem

Methaemoglobinaemia is now rare in most of the industrialised countries due to control of nitrate contamination in water supplies, although occasional cases continue to be reported from rural areas. It is a risk in developing countries, for example where the drinking water is from shallow wells in farming areas.

There is no reliable estimate of the extent of the problem worldwide. WHO is presently collecting information in order to make such an estimate.

Interventions

Control of nitrate in drinking water is an effective preventive measure. WHO's Guideline Value for nitrate in drinking water is 50 mg /litre and for nitrite is 3mg/litre. This is relatively readily achieved in centralised, piped, supplies, but is difficult in rural and small supplies.

The group at greatest risk is bottle fed infants. Breastfeeding protects babies from methaemoglobinaemia. Boiling water does not remove nitrate.

For severely affected individuals, medical treatment is possible.

References

McDonald A T, Kay D. Water resources issues and strategies. UK: Longman Scientific and Technical, 1988, p 146-148

Super M, Heese HV , Mackenie D et al. An epidemiological study of well water nitrates in a group of South West African /Namibian infants. Water Research, 1981: 15: 1265-70

World Health Organization. WHO Guidelines for drinking water quality. 2nd edition, addendum to Volume 1: Recommendations. Geneva: WHO, 1998, p-8-10; and addendum to Volume 2: Health Criteria and other Supporting Information.

Onchocerciasis

Onchocerciasis or river blindness is a parasitic disease with an insect vector that breeds in water. It is the world's second leading infectious cause of blindness. Controlling insect breeding sites in rivers is one of the pillars of prevention.

The disease and its cause

Onchocerciasis or river blindness is a parasitic disease caused by Onchocerca volvulus, a thin parasitic worm that can live for up to 14 years in the human body. The disease is transmitted from one person to another through the bite of a blackfly (Simulium).

The blackfly lays its eggs in the water of fast-flowing rivers, which mature into adult blackflies in 8 to 12 days. The female blackfly typically seeks a bloodmeal after mating and, upon biting a person who is infected with onchocerciasis, may ingest worm larvae, which can then be passed on to the next person bitten by the blackfly. Eventually, the transmitted worm larvae develop into adult worms and settle into fibrous nodules in the human body close to the surface of the skin or near the joints.

Effect on people

Each adult female worm (macrofilaria), which can be more than ½ metre in length, produces millions of microscopic young worms (microfilariae). The microfilariae migrate through the skin and, upon death, cause intense itching and depigmentation of the skin (“leopard skin”), lymphadenitis resulting in hanging groins and elephantiasis of the genitals, serious visual impairment, and blindness when they reach the eye

Symptoms of the disease in a person usually begin to show 1-3 years after infection.

Distribution

Onchocerciasis is found in 36 countries in Africa as well as in Guatemala, southern Mexico, some areas of Venezuela, small areas in Brazil, Colombia and Ecuador, and in the Arabian peninsula.

Scope of the Problem

Onchocerciasis is the world's second leading infectious cause of blindness. A total of 18 million people are affected worldwide. Of those affected outside the area in West Africa covered by the Onchocerciasis Control Programme, over 6.5 million suffer from severe itching or dermatitis and 270 000 are blind.

Interventions

There are two main actions undertaken against onchocerciasis control: spraying of breeding sites in water of the blackflies with larvicides, and the treatment of patients with a drug (ivermectin) that kills the young worms.

The Onchocerciasis Control Programme in West Africa (OCP)

The Onchoceriasis Control Programme in West Africa (OCP), jointly sponsored by WHO, the World Bank, the United Nations Development Programme and the UN Food and Agriculture Organization, and supported by a coalition of 20 donor countries and agencies, was launched in 1974 and currently covers a total population of about 30 million people in 11 countries.

OCP has been working to control onchocerciasis of interrupting the parasite transmission cycle. The blackfly larvae are destroyed by the application of larvicides through aerial spraying of breeding sites in fast-flowing rivers so that they do not develop into blackflies capable of transmitting the parasite. Since 1987, the use of ivermectin in combination with aerial larviciding has had a remarkable impact on the transmission of the disease and greatly reduced the effect on humans.

When the programme was launched 27 years agoAt the beginning of the programme, 1 million people in West Africa suffered from onchocerciasis, 100 000 of these had serious eye problems (including 35 000 who were blind). It is expected that by the end of the year 2002, when the programme is scheduled to come to an end, onchocerciasis will be eliminated as a public health problem and as an obstacle to socioeconomic development in this area.

Other Control Programmes

With the African Programme for Onchocerciasis Control (APOC) launched in December 1995, control efforts are ongoing in 19 other African countries outside the 11 countries of OCP. APOC intervention is based mainly on treatment with ivermectin entirely planned and managed by the communities themselves. The objective of the programme is primarily to establish within a 12 to 15-year period an effective and self-sustainable drug distribution mechanism within the communities in the endemic areas.

In 1992, the Onchocerciasis Elimination Program in the Americas (OEPA) was launched in 6 countries. Ivermectin distribution has been the main intervention strategy and the programme is now in the process of preparing for certification of the elimination of onchocerciasis in those countries.

Ringworm (Tinea)

Ringworm or Tinea is a typically mild disease of the skin, scalp or nails caused by a fungus. Personal hygiene, supported by availability of adequate quantities of water are important preventive measures.

The disease and how it affects people

Ringworm is a contagious skin disease, in which the scalp (tinea capitis), nails (tinea unguium), feet (tinea pedis or “athlete's foot”), or body (tinea corporis) can be affected. Despite its name, ringworm is caused by a fungus.

On the scalp, ringworm begins in the form of a pimple or sore, which then spreads into a ring shape. Hair becomes brittle, breaking easily and falling out, leaving bald spots on the scalp. On the body, ringworm may first appear as red or pink, flat or slightly raised, patches on the skin. The circular sores may be dry or scaly crusted or moist. As the sores become larger, the central area clears, leaving a ring of infected tissue around the clear area. Infection in the nails usually begins at the site of an injured nail and may spread to the other nails. Infected nails become thick, pitted, grooved and abnormal in shape and colour.

Ringworm of the feet and body are more frequent in men than women. Adults are more likely than children to get ringworm of the feet, which occurs more frequently in hot weather.

The cause

Ringworm is caused by various types of fungi known as the dermatophytes. It is spread by direct contact with an infected person or animal (dogs, cats, guinea-pigs, cattle), contact with soil or by indirect contact with items contaminated by the fungus, for example clothing, towels, bedclothes, chairs, and toilet articles handled by people with the infection. The link with water is via poor personal domestic hygiene and shortage of water for cleaning and washing.

Distribution

The various types of ringworm are found worldwide.

Scope of the Problem

Although specific figures are not available, ringworm is a frequent problem in most countries, particularly where personal and domestic hygiene are poor.

Interventions

Key components of prevention are:

• An adequate supply of water for personal washing and hygiene.
• Regular and thorough bathing with soap and water, with special attention to drying moist areas.
• Health education about how its spreading can be prevented.

Where ringworm occurs:

• The clothing and linen of infected persons should be frequently laundered in hot water to rid them of the fungus.
• Rashes can be treated with topical anti-fungal lotions or creams. In severe or persistent cases oral anti-fungal medication may be required.

Scabies

Scabies is a contagious skin infection that spreads rapidly in crowded conditions and is found worldwide. Personal hygiene is an important preventive measure and access to adequate water supply is important in control.

The disease and how it affects people

The principal sign of the disease is a pimple-like rash that is most commonly found on the hands, especially the webbing between the fingers, the skin folds of the wrist, elbow or knee, the penis, the breast or the shoulder. Infestation often causes intense itching all over the body, especially at night. Scratching of itchy areas results in sores that may become infected by bacteria. A more severe form of scabies, known as Norwegian scabies, is more common among people with weakened immune systems. In this form of the disease, vesicles are present along with thick crusts over the skin. The itching in this type of scabies may be less severe or totally absent.

The cause

Scabies infestation is caused by the microscopic mite Sarcoptes scabei. The fertilized female mite burrows into the skin, depositing eggs in the tunnel behind her. After the eggs are hatched, larvae migrate to the skin surface and eventually change into the adult form. Mating occurs on the skin surface. An adult mite can live up to about a month on a person. Once away from the human body, mites only survive 48-72 hours. The characteristic itchy rash of scabies is an allergic response to the mite. Individuals who are infested with scabies for the first time typically experience symptoms after 4 to 6 weeks. With subsequent infestation, symptoms appear within days.

Scabies spreads principally by direct skin-to-skin contact and to a lesser extent through contact with infested garments and bedclothes. Environments that are particularly vulnerable to the spread of scabies include hospitals, childcare facilities and any crowded living conditions. Infestation is easily passed between sexual partners.

Distribution

Scabies mites are found worldwide, affecting all socioeconomic classes and in all climates. Epidemics have been linked to poverty, poor water-supply, sanitation and overcrowding.

Scope of the Problem

There are about 300 million cases of scabies in the world each year.

Interventions

Improved personal hygiene plays an important part in the prevention and control of scabies and depends on access to adequate water-supply. Treatment of patients is with acaricide ointments preceded by a hot bath with liberal use of soap. Infested clothing should be sterilized or washed in hot soapy water. Bedding, mattresses, sheets and clothes may require dusting with acaricides.

Several recent studies have demonstrated that an oral dose of ivermectin is extremely effective in curing scabies. The mass distribution of ivermectin organized by WHO for the control of onchocerciasis and lymphatic filariasis (in this case associated with albendazole) could have an important impact on scabies.

Schistosomiasis

The disease and how it affects people

Schistosomiasis is a water-based disease which is considered the second most important parasitic infection after malaria in terms of public health and economic impact. The signs following infection are rashes or itchy skin. Two months after infection, fever, chills, cough and muscle aches may occur, as the parasites mature. Untreated infections can result in blood in urine and stools, and enlarged liver and spleen. In children there is a negative impact in terms of growth, nutritional status and cognitive development. Chronic infection leads to diseases of the liver, kidneys and bladder. Occasionally, the nervous system is affected causing seizures, paralysis or spinal cord inflammation.

The cause

Schistosomiasis infection in humans, the definitive hosts, is caused by three main species of flatworm, namely Schistosoma haematobium, S. japonicum, and S. mansoni. In Asia, cattle and water buffalo can be important reservoir hosts. Infection occurs when free-swimming larvae penetrate human skin. The larvae develop in fresh-water snails. Humans are infected when they enter larvae-infested water for domestic, occupational and recreational purposes. After skin penetration, the larvae transform and are carried by the blood to the veins draining the intestines or the bladder where they mature, mate and produce eggs. Eggs cause damage to various tissues, particularly the bladder and liver. The reaction to the eggs in tissues causes inflammation and disease. When infected humans excrete parasite eggs with feces or urine into water, the eggs hatch releasing larvae that in turn infect aquatic snails. In the snail the parasite transforms and divides into second-generation larvae which are released into fresh water ready to infect humans. Those who work in irrigation or fishing are at increased risk for schistosomiasis. With the increase in wilderness or “off-track” tourism, more tourists are becoming infected.

Distribution

Schistosomiasis is endemic in 76 countries, most of which are in Africa. Other regions affected are: the Americas (Brazil, Suriname and Venezuela, as well as several Caribbean islands); the Eastern Mediterranean (Islamic Republic of Iran, Iraq, Saudi Arabia, Syrian Arab Republic and Yemen; and eastern Asia (Cambodia, China, Indonesia, Japan, Lao People's Democratic Republic and the Philippines.

Scope of the Problem

At least 600 million people are at risk of infection and 200 million are infected with schistosomiasis. Of these 20 million have severe disease and 120 million have symptoms. An estimated 80% of transmission takes place in sub-Saharan Africa. Water resource schemes for power generation and irrigation have resulted in a tremendous increase in the transmission and outbreaks of schistosomiasis in several African countries. In northern Senegal, an area without intestinal schistosomiasis before the building of the Diama dam in 1986, virtually the whole population had become infected by 1994.

Interventions

Improved sanitation and potable water minimizes contamination of and reduces contact with fresh water, thus limiting transmission. Environmental modification preventing snail vectors and limiting human water contact offers long-term control of schistosomiasis. Health education is a fundamental component that ensures community participation in control interventions. In areas of high prevalence and intensity of infection, chemotherapy with praziquantel, targeted at school-age children and high-risk groups, offers the most efficient way to achieve the recommended strategy for morbidity control. Proper health impact assessment of new irrigation schemes and other water resources projects will provide a solid basis for the incorporation of health safeguards at design and construction plans.

Trachoma

The disease and how it affects people

Trachoma is an infection of the eyes that may result in blindness after repeated re-infections. It is the world's leading cause of preventable blindness and occurs where people live in overcrowded conditions with limited access to water and health care. Trachoma spreads easily from person to person and is frequently passed from child to child and from child to mother within the family. Infection usually first occurs in childhood but people do not became blind until adulthood. The disease progresses over years as repeated infections cause scarring on the inside of the eyelid, earning it the name of the “quiet disease” The eyelashes eventually turn in. This causes rubbing on the cornea at the front of the eye. The cornea becomes scarred leading to severe vision loss and eventually blindness.

The cause

Trachoma is caused by an organism called Chlamydia trachomatis. Through the discharge from an infected child's eyes, trachoma is passed on by hands, on clothing, or by flies that land on the face of the infected child.

Distribution

Trachoma occurs worldwide and most often in poor rural communities in developing countries. Blinding trachoma is widespread in the Middle East, North and Sub-Sahara Africa, parts of the Indian subcontinent, Southern Asia and China. Pockets of blinding trachoma occur in Latin America, Australia (among native Australians) and the Pacific Islands.

Scope of the Problem

The World Health Organization (WHO) estimates that six million worldwide are blind due to trachoma and more than 150 million people are in need of treatment.

Interventions

Primary interventions advocated for preventing trachoma infection include improved sanitation, reduction of fly breeding sites and increased facial cleanliness (with clean water) among children at risk of disease. The scaring and visual change for trachoma can be reversed by a simple surgical procedure performed at village level which reverses the inturned eyelashes.

Good personal and environmental hygiene has been proven to be successful in combating trachoma. Encouraging the washing of children's faces, improved access to water, and proper disposal of human and animal waste has been shown to decrease the number of trachoma infections in communities.

Global Alliance for the Elimination of Trachoma by the year 2020 (GET 2020)

The WHO along with an alliance of interested parties has adopted the “SAFE” strategy to combat trachoma. The four components of the strategy include:

• Surgery
• Antibiotic treatment (Tetracycline eye ointment new antibiotic, azithmycin has been tested in a number of countries and initial results are very promising
• Facial cleanliness
• Environmental changes.

Typhoid and paratyphoid enteric fevers

Typhoid and paratyphoid fevers are infections caused by bacteria which are transmitted from faeces to ingestion. Clean water, hygiene and good sanitation prevent the spread of typhoid and paratyphoid. Contaminated water is one of the pathways of transmission of the disease.

The disease and how it affects people

Typhoid fever is a bacterial infection of the intestinal tract and bloodstream. Symptoms can be mild or severe and include sustained fever as high as 39°-40° C, malaise, anorexia, headache, constipation or diarrhoea, rose-coloured spots on the chest area and enlarged spleen and liver. Most people show symptoms 1-3 weeks after exposure. Paratyphoid fever has similar symptoms to typhoid fever but is generally a milder disease.

The cause

Typhoid and paratyphoid fevers are caused by the bacteria Salmonella typhi and Salmonella paratyphi respectively. Typhoid and paratyphoid germs are passed in the faeces and urine of infected people. People become infected after eating food or drinking beverages that have been handled by a person who is infected or by drinking water that has been contaminated by sewage containing the bacteria. Once the bacteria enter the person’s body they multiply and spread from the intestines, into the bloodstream.

Even after recovery from typhoid or paratyphoid, a small number of individuals (called carriers) continue to carry the bacteria. These people can be a source of infection for others. The transmission of typhoid and paratyphoid in less-industrialized countries may be due to contaminated food or water. In some countries, shellfish taken from sewage-contaminated beds is an important route of infection. Where water quality is high, and chlorinated water piped into the house is widely available, transmission is more likely to occur via food contaminated by carriers handling food.

Distribution

Typhoid and paratyphoid fevers are common in less-industrialized countries, principally owing to the problem of unsafe drinking-water, inadequate sewage disposal and flooding.

Scope of the Problem

The annual incidence of typhoid is estimated to be about 17 million cases worldwide.

Interventions

Public health interventions to prevent typhoid and paratyphoid include:

• health education about personal hygiene, especially regarding hand-washing after toilet use and before food preparation; provision of a safe water supply;
• proper sanitation systems;
• excluding disease carriers from food handling.

Control measures to combat typhoid include health education and antibiotic treatment. A vaccine is available, although it is not routinely recommended except for those who will have prolonged exposure to potentially contaminated food and water in high-risk areas. The vaccine does not provide full protection from infection.