Water-borne diseases are caused by water that is contaminated with microorganisms. The microbes—typically bacteria, viruses, protozoa, and parasites—are usually found in the intestinal tracts of humans and other creatures. In most cases, the water becomes contaminated by feces that carry the microbes.
Over 1 billion people worldwide do not have access to safe drinking water, and 3.4 million people die each year due to water-borne diseases, according to the World Health Organization (WHO). Indeed, water-borne diseases are the most common cause of disease and death in the world, according to the WHO. While this is largely a problem in developing and underdeveloped countries, developed nations, including the United States, are not immune. An estimated 900,000 water-borne-related illnesses and almost 1,000 deaths occur in the United States each year, according to the U.S. Centers for Disease Control and Prevention (CDC).
As noted above, water-borne diseases are caused by a wide range of pathogens, including bacteria, viruses, parasites, and protozoa. Examples of bacteria that are important water-borne pathogenic organisms include Vibrio cholerae (the bacteria that causes cholera), various species Campylobacter, Salmonella, Shigella, and a type of Escherichia coli designated O157:H7.
An example of a pathogenic water-borne virus is the norovirus, which has become notorious in causing disease outbreaks on cruise ships, and in day care centers and universities. In the winter of 2007, classes were interrupted at two universities in the Canadian province of Nova Scotia because of simultaneous outbreaks of water-borne norovirus diarrhea. Viruses that normally dwell in the intestinal tract are also capable of causing disease if they contaminate water. Just one example is hepatitis (several forms of hepatitis are caused by several types of hepatitis virus).
As occurred in the Nova Scotia incidents, waterborne diseases are often the result of drinking or bathing in contaminated freshwater. Saltwater-borne microbial diseases also exist, and bacteria, viruses, and algae are typically associated with these illnesses. Explosive growth of certain algal species in ocean water can lead to the accumulation of these algae in oysters and other shellfish that feed by filtering water. If people eat the affected shellfish, various diseases can result. Some of these can be serious, producing paralysis and death.
Amebiasis is a common water-borne disease that is caused by the parasite Entamoeba histolytica. This parasite is normally found in feces, and can cause disease when fecal-contaminated water is consumed. About one of every 10 people who consume E. histolytica—which translates to millions of people worldwide—becomes ill. Their symptoms can be mild (diarrhea, stomach ache, and cramping), but, in some people, a severe form of amebiasis called amebic dysentery develops. The destruction of cells lining the intestinal tract produces bloody diarrhea. More rarely, the parasite can spread to the liver, lungs, or the brain.
Cryptosporidiosis is another water-borne disease caused by a parasite. This illness is caused parasites of the genus Cryptosporidium, especially C. parvum. The organism's life cycle consists of a small, inert form and an actively growing form. The inert form can pass through the filters used in water treatment plants and can survive exposure to chlorine. Once inside a person, the resulting infection can persist for months despite treatment.
Once relatively rare, cryptosporidiosis increased in prevalence in the United States beginning in the 1980s, as expansion of urban areas brought more people into contact with the animals that naturally harbor the parasite in their intestinal tracts. Symptoms of cryptosporidiosis include dehydration, persistent stomach upset, weight loss, nausea, and vomiting. The parasite can be passed from person to person. As of 2007, cryptosporidiosis is one of the most common causes of water-borne disease in the United States. A well-known outbreak occurred in Milwaukee, Wisconsin, in 1993; over 200,000 people were sickened during this outbreak.
Yet another parasite-mediated water-borne disease is cyclosporiasis, which is caused by Cyclospora cayetanensis. A hallmark of this infection is the sudden and explosive diarrhea that repeatedly occurs. Other symptoms include weight loss, dehydration, stomach upset, and fatigue.
Giardiasis is a disease caused by an intestinal parasite called Giardia lamblia (sometimes called Giardia intestinalis). Over the past 20 years, this disease has become one of the most common water-borne human diseases in the United States. In North America, it is sometimes known as beaver fever, since the beaver is one of the animals that naturally harbor the parasite in their intestinal tracts. Symptoms of giardiasis include diarrhea, intestinal gas, stomach cramps, upset stomach, and nausea. The lingering intestinal upset of giardiasis can be debilitating.
Water-borne diseases caused by microorganisms occur worldwide. Virtually every country experiences water-borne illnesses, although the diseases tend to be more prevalent in tropical countries where the warmer climate favors the persistence of bacteria and viruses that enter the water from the intestinal tract. water-borne diseases are especially problematic in developing and underdeveloped nations, where adequate water treatment facilities may be lacking and safe drinking water may be in short supply. For example, in 2000, about 140,000 cases of cholera were reported to the WHO, and these infections resulted in 5,000 deaths. About 87% of these cases occurred in Africa.
Drinking water can be treated to remove or destroy contaminating microorganisms. Chlorination, one wellknown treatment, destroys pathogenic bacteria, nuisance bacteria, parasites, and other organisms. Others treatments include exposure of the water to ultraviolet light (which rearranges the microbes’ genetic material so that they cannot reproduce) and ozone, and the passage of water through a filter whose openings are so small that even viruses are removed.
Water-borne diseases that are caused by bacteria, protozoa, and some parasites can be treated using compounds that kill the target organism. For example, anti-biotics are effective against bacteria. Viruses are more problematic, since antibiotics are not effective.
The best strategy is not to treat an infection, but to avoid getting the infection. Sensible precautions include washing hands after having a bowel movement, never drinking water that has not been treated (if in doubt, do not drink), and avoiding bathing or swimming in water that is known to be polluted. In many North American and European communities, recreational water is monitored and notices are posted restricting swimming when the water is determined to be contaminated.
The global impact of water-borne disease is huge. The U.S. Centers for Disease Control and Prevention (CDC) estimates that there are over 4 billion episodes of diarrhea due to the consumption of contaminated water, and more than 2 million deaths. Tragically, most of these deaths occur among children in developing and under-developed countries. The WHO estimates that 4,000 children die every day from water-borne diseases. According to the CDC and the WHO, more than 2 billion people living in poverty are especially susceptible to water-borne disease, mainly due to contaminated surface water or inadequately treated drinking water.
People whose immune systems are not operating efficiently can develop more severe or persistent forms of water-borne diseases, such as cryptosporidiosis. The latter has become a significant threat for people with acquired immunodeficiency syndrome (AIDS, also cited as acquired immune deficiency syndrome) and those who take immunosuppressive drugs to reduce the chance of rejection of a transplanted organ.
Aside from the human tragedy, this massive loss of life robs countries of the next generation of citizens and workers, which has serious consequences for the future population level and economic strength of these nations. For such nations, water treatment must be a priority. Analysts at the WHO and other agencies have estimated that for every dollar spent on water treatment, the economic return due to lower rates of death and disease would be $3–$4 per country. The resulting economic boost could help lift some nations out of poverty.
WORDS TO KNOW
CHLORINATION: Chlorination refers to a chemical process that is used primarily to disinfect drinking water and spills of microorganisms. The active agent in chlorination is the element chlorine, or a derivative of chlorine (e.g., chlorine dioxide). Chlorination is a swift and economical means of destroying many, but not all, microorganisms that are a health-threat in fluid such as drinking water.
DIARRHEA: To most individuals, diarrhea means an increased frequency or decreased consistency of bowel movements; however, the medical definition is more exact than this explanation. In many developed countries, the average number of bowel movements is three per day. However, researchers have found that diarrhea, which is not a disease, best correlates with an increase in stool weight; stool weights above 10.5 ounces (300 grams) per day generally indicates diarrhea. This is mainly due to excess water, which normally makes up 60 to 85% of fecal matter. In this way, true diarrhea is distinguished from diseases that cause only an increase in the number of bowel movements (hyperdefecation), or incontinence (involuntary loss of bowel contents). Diarrhea is also classified by physicians into acute, which lasts one to two weeks, and chronic, which continues for longer than four weeks. Viral and bacterial infections are the most common causes of acute diarrhea.
FECES: Solid waste of a living body.
NOROVIRUS: Norovirus is a type of virus that contain ribonucleic acid as the genetic material, and which causes an intestinal infection known as gastroenteritis. A well-known example is Norwalk-like virus.
PATHOGEN: A disease causing agent, such as a bacteria, virus, fungus, etc.
The problem of water-borne disease is not confined to the poor regions of the globe, however. Even in developed countries, a breakdown of water treatment can lead to disease. A well-known recent example occurred in the Canadian community of Walkerton, Ontario, in the summer of 2000. The accidental flooding of a community well with run-off from a cattle farm, combined with inadequate treatment of the drinking water led to an outbreak of E. coli O157:H7-mediated illness that sickened over 2,000 people and killed seven. Some of the survivors were left with permanent damage to their kidneys due to the destructive effects of a toxin produced by the bacteria.
IN CONTEXT: DISEASE IN DEVELOPING NATIONS
Contaminated clean water supplies are often a major factor in the spread of disease. Besides climate, the most common reasons for clean water shortages are caused primarily by human activity. Water pollution can occur from both industry and leaking of septic (waste) water into the water supply system. In both cases, the water may become dangerous for the health of the people and unusable for industry. Purification of industrial waste is expensive, and sometimes, economic interests may conflict with protecting the environment. Many developing countries cannot afford proper water purification because their main concern is survival rather than the quality of the environment. Pollution, however, is a global concern and affects people in other countries besides the source of the pollution.
In many countries, drinking water is monitored to ensure that it is free from pathogenic bacteria, viruses, and protozoa. In the United States, CDC surveillance programs detect water-borne outbreaks and help direct federal, state, and municipal responses to the outbreaks. Similar efforts in developing and underdeveloped countries have been far less successful, as population increases in these poorer countries have outstripped the economic capability of governments to put in place the necessary water treatment technologies. By 2015, the United Nations has set a goal of cutting the number of people without access to safe drinking water by 50%.
Despite the continuing challenges, some successes have occurred. Initiatives such as the CDC's Healthy Drinking Water Program, the United Nations International Decade for Action: Water for Life 2005–2015, and the WHO's household water treatment and safe storage network are bringing simple and relatively inexpensive water treatment methods to rural areas in Africa, Central America, and South America, and helping to safeguard water in the United States. As one example, a disease called drancunculiasis, which formerly affected almost 4 million people each year in African countries, has been almost eliminated. As of 2007, the disease is detectable in only 12 nations in Africa.
See AlsoAmebiasis; Bacterial Disease; Campylobacter Infection; Cholera; Cryptosporidiosis; Cyclosporiasis; Dracunculiasis; Dysentery; Escherichia coli O157:H7; Giardiasis; Mosquito-Borne Diseases; Norovirus Infection; Salmonella Infection (Salmonellosis); Shigellosis; Viral Disease.
Ewald, Paul. Plague Time: The New Germ Theory of Disease. New York: Anchor, 2002.
Percival, Steven, et al. Microbiology of water-borne Diseases: Microbiological Aspects and Risks. New York: Academic Press, 2004.
Powell, Michael, and Oliver Fischer. 101 Diseases You Don't Want to Get. New York: Thunder's Mouth Press, 2005.
Centers for Disease Control and Prevention.
“Water-borne Diseases.” October 23, 2001. <http://www.cdc.gov/ncidod/diseases/list_water-borne.htm> (accessed April 19, 2007).