Waterborne diseases are those caused by exposure to pathogens found in water. The water can be used for drinking, cooking, washing, or swimming. Many waterborne diseases are diarrheal illnesses.
Contaminated water is one of the leading causes of illness worldwide. Open defecation (defecating in the open instead of in contained latrines or toilets) allows the easy spread of pathogens. Diarrheal diseases are one of the leading causes of death in children under the age of five worldwide. Repeated bouts of diarrhea can lead to malnutrition in children and adults, which increases the incidence of acute respiratory infections, the leading cause of deaths in developing countries.
Human feces can contain a variety of pathogens: viruses, bacteria, protozoan cysts, flatworm eggs, and larvae. Bacterial diseases include cholera, dysentery, legionellosis, leptospirosis, campylobacteriosis, salmonellosis, typhoid fever, and vibriosis. Viral diseases include hepatitis A, poliomyelitis, and severe acute respiratory syndrome (SARS). Protozoans cause amoebiasis, giardiasis, cyclosporiasis, and cryptosporidiosis. Guinea worm disease and schistosomiasis are caused by parasitic worms. Many waterborne diseases are zoonotic, carried in animals and transmitted from reservoirs (animal hosts that carry a pathogen without themselves getting sick) to humans by vectors (animals, especially arthropods, that transfer a pathogen from one animal to another).
According to the WHO, waterborne diseases cause two million deaths worldwide every year, most of those in children under five.
The U.S. Centers for Disease Control and Prevention (CDC)'s Waterborne Disease Prevention Branch coordinates a domestic and global effort to combat waterborne diseases. It identifies 11 pathogens as part of the water, sanitation, and hygiene (WASH)-related diseases. These include amebiasis, cryptosporidiosis, giardiasis, cholera, shigellosis, and infections caused by Cronobacter, enterotoxigenic Escherichia coli, and the free-living amebae Acanthamoeba, Balamuthia, Naegleria, and Sappinia. The CDC tracks diseases in the United States, investigates outbreaks, and creates new ways to prevent diseases.
The United Nations recognized sanitation and clean water as human rights and has called on the international community to help developing nations provide these things for their people. In 2013, it pledged an end to open defecation by 2050. According to the WHO, in 2015, 68% of the world's people had access to improved sanitation facilities (flush toilets or covered latrines), up from 54% in 1990. Nearly one billion people still practiced open defecation, but the percentage has dropped from 24% to 13% since 1990. The WHO has calculated that every dollar invested in sanitation provides a return of over five dollars in lower health costs and improved productivity.
Poverty is the biggest risk factor for poor sanitation and contaminated drinking water. Open defecation, lack of water purification or sewage treatment systems, fertilizing agricultural fields with human waste, and densely populated urban slums are all factors making waterborne disease more likely.
Climate change causes increased flooding, which can increase incidence of waterborne diseases. Water shortages during droughts also increase the risk of waterborne diseases.
There is a huge range of waterborne diseases. Many are caused by the fecal-oral route of transmission, in which pathogens in feces enter the water or food supply, where they can be swallowed; diarrhea is an extremely common symptom of these diseases, and contributes to the perpetuation of the disease cycle. Other waterborne diseases travel more circuitous routes, involving animal vectors and reservoirs and complex life cycles.
Giardiasis is caused by a protozoan in the genus Giardia, which is found in water, food, or soil. The Giardia organism is encased in a protective shell that allows it to survive in dry areas and to resist chlorine disinfection. It enters the digestive tract when a person drinks water contaminated with feces from an infected animal or human.
Giardiasis causes diarrhea, greasy stools, gas, abdominal cramps, nausea and vomiting, and dehydration. Symptoms can last for weeks. Giardiasis is the most common intestinal parasite in the United States and a common cause of traveler's diarrhea.
Schistosomiasis, also called bilharzia, is caused by parasitic worms that live in freshwater snails. When a person, typically a school-age child, swims or bathes in water infested with snails, the infectious cercariae (larval worms) can penetrate the skin and take up residence in the veins. The adult worms live in the small or large intestine or the bladder, and eggs are eliminated in urine or feces. Several days after infection, the victim may develop itchy skin or a rash. After a month or two, symptoms such as fever, chills, cough, and muscle aches develop. The disease can persist for years, causing abdominal pain, blood in the urine or stool, an enlarged liver, and damage to the intestine, spleen, bladder, and lungs. Repeated infections can cause malnutrition and anemia, with accompanying learning difficulties.
Leptospirosis is caused by infection with Leptospira bacteria. These bacteria are commonly found in animals, including cattle, pigs, horses, dogs, and rodents. The animals excrete the bacteria in their urine, and humans pick it up by coming into contact with contaminated water, especially floodwaters. The bacteria enters the skin through cuts and scratches, through the mucous membranes, or through drinking.
The incubation period ranges from two days to four weeks. Symptoms include high fever, chills, headache and muscle aches, vomiting and diarrhea, jaundice, and rash. The patient can seem to recover and then enter a second phase of the disease which can involve meningitis or kidney or liver failure. Recovery takes several months.
Shigellosis is caused by Shigella bacteria, which spreads through oral-fecal contact. Shigellosis causes about 500,000 cases of diarrhea every year in the United States, but is a much more serious problem in the developing world. Symptoms include diarrhea (maybe bloody), abdominal pain, fever, and a sense of needing to pass stools when bowels are empty. Symptoms last five to seven days, but bowel symptoms can linger for months. A few patients develop complications such as arthritis, seizures, or infections of the blood stream.
Hepatitis A is a liver infection caused by a virus. It is shed in feces and transmitted through oral contact with feces, either through contaminated water and food or through physical contact. Common ways of acquiring the virus include travel to places where hepatitis A is common, using illegal drugs, and sexual contact. The CDC reports that there were about 2500 cases of Hepatitis A in the United States in 2014. Rates have gone down since a vaccine was introduced in 1995.
Symptoms include fever, nausea, vomiting, fatigue, dark urine, clay-colored stool, and jaundice. Symptoms appear two to six weeks after exposure. They can last for weeks or months. Most people recover completely.
Diarrhea is a very common symptom of waterborne diseases. Other symptoms, along with a history of travel and exposure to pathogens, can help narrow down a specific diagnosis.
Giardiasis can be diagnosed by finding eggs and parasites in the stool; three samples should be taken on separate days to increase the chances of finding some. Schistosomiasis can be diagnosed though examination of stool or urine samples, which might contain eggs.
A blood test is the most reliable way to diagnose schistosomiasis and hepatitis A. With shigellosis, a laboratory test can determine whether the causative bacterium is resistant to specific antibiotics.
Giardia can be treated with metronidazole, tinidazole, and nitazoxanide. Schistosomiasis can be treated with praziquantel. Shigellosis usually needs no treatment; antibiotics are helpful in severe cases, but Shigella is resistant to many types of antibiotics.
Prognosis depends on the disease and its severity. Waterborne diseases are common and people regularly recover, but repeated bouts of illness take their toll and can cause permanent impairments. Serious diarrhea can be deadly.
Good sanitation is the best prevention for waterborne diseases. Containing feces in latrines or sewers, washing hands and food with clean water, and avoiding swimming or wading in potentially contaminated freshwater are important. Vigorous towel drying after swimming in freshwater can sometimes remove the snails that cause schistosomiasis from the skin.
In countries without municipal water systems, individuals can use the CDC's Safe Water System (SWS) to treat and store water in their homes. Water treatment options include chlorination, disinfectant powder, solar disinfection, or filtration through sand or ceramic. Treated water is stored in a plastic, ceramic, or metal container with a lid and a small opening or spigot so that people cannot put their hands into the water.
See also Bacterial diseases; Cholera ; Cryptosporidiosis ; Escherichia coli ; Helminth diseases; Leptospirosis ; Parasitic diseases ; Protozoan diseases; Salmonella; Schistosomiasis ; Shigellosis ; Typhoid fever ; Vibriosis ; Water and sanitation.
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Amy Hackney Blackwell, PhD