: 3. Disease Causing Agents

Disease causing agents include viruses and bacteria, protozoa, worms and now dinoflagellates and diatoms that either enter from domestic sewage and animal wastes or thrive in conditions which give them a competitive edge.

The extent of the problem:

More than one billion people worldwide drink unsafe water, A total of 3.4 million people, mostly children, die every year from water-related diseases from drinking, swimming in or washing clothes in polluted water. Diseases include malaria, diarrhea and guinea worm.

This is to be expected in LDC's, but does the US also have problems with parasites? read the article below...

Americans have been busy protecting their waters from chemical pollution, but microbes such as viruses and bacteria pose a much greater threat.

 Such dangerous organisms include E. coli O157, cryptosporidium,giardia, hepatitis A and pfiesteria, the report, from the American Society for Microbiology, said. "Control of water pollution in the United States over the past two decades has focused on chemical risks, overshadowing the significant risks associated with microbial pollutants,"

According to the Centers for Disease Control and Prevention, as many as 900,000 people get sick and 900 die every year in the United States because of waterborne microbial infections.

 E. coli bacteria can kill, as can legionella, which causes Legionnaire's disease, a respiratory illness. Cholera, salmonella and shigella are all bacteria that cause diarrhea and sometimes death. Parasites such as Giardia cause diarrhea and can lead to lactose intolerance and severe joint pain, while cryptosporidium, which also causes diarrhea, can kill weak victims.

 Viruses range from hepatitis A, which can cause liver failure, to coxsackieviruses, which can cause a deadly heart inflammation and sometimes even diabetes, while echoviruses cause meningitis.

 Much of the contamination comes from the practice of pumping human waste into rivers or oceans, or letting them filter into groundwater. "A small drop of fecal matter can contain millions of these microorganisms," the report said.  "There are approximately 25 million septic tanks in the United States, receiving 175 billion gallons of wastewater that could contaminate ground and surface waters with viruses and other pathogens," it added. It said viruses had been found in 20 percent of groundwaters tested nationwide.

 Farming also pollutes waters. "Cattle can excrete millions of E. coli O157, cryptosporidium, giardia and other microbes," he report said. "Chicken wastes carry the pathogenic bacteria salmonella and campylobacter."

 The report points out that the EPA's standards for drinking water name at least 70 chemicals, but only one microbe -- coliform bacteria, which include the E. coli family.

Sewage treatment plants are supposed to filter out or destroy microorganisms, but do not always succeed, the report adds. "Thus the wastewaters released could still contain enough pathogenic microorganisms to threaten human health," it says. Joan Rose, a marine biologist at the University of South

Florida who helped write the report, said she found nasty bugs sometimes present in feces wind up right offshore within 12 to 24 hours of being flushed. The report called for coordinated national action by the EPA, the Food and Drug Administration and other agencies. "There is a critical need for an integrated national initiative on the microbial quality of water and on risk assessment as related to public health," it concluded. Source: Reuters

And if that isn't enough..........


 Scientists reported Wednesday they have found the first direct link between drinking water and stomach ulcers. The finding came from tests done on wells and other water sources in Pennsylvania where the bacteria Helicobacter pylori was found. The bacteria is known to cause certain gastric ulcers.

 The report from Pennsylvania State University in Harrisburg said interviews with residents who consumed the water found a statistically significant correlation between presence of the bacteria and cases of stomach ulcers. Katherine Baker who led the research said drinking water is generally considered safe when coliform bacteria is not present. But the ulcer-causing bacteria was found in coliform-free water samples, she said.

"What this really means is that our current methods for testing drinking water may be saying that water is fine while H. pylori may actually be present," she said. Baker said the study involved private, untreated water supplies ( approx. 25% of US water supplies are considered rural) and not municipal water sources, which are less likely to contain the organism. .......Source: Reuters

Cryptosporidium : Specific noted cases of outbreaks in the US include:

Examples: In 1993 the worst outbreak of a water born disease in modern US history occurred in Milwaukee, Wisconsin. Severe bouts of watery diarrhea struck an estimated 403,000 people.

August 1998 An estimated 1,300 people in a suburban area north of Austin may have been infected with a potentially fatal parasite that could have been distributed through the public drinking water system for as long as a week, health officials say. The parasite comes from the feces of wild and domestic animals and is found in up to 87 percent of untreated water supplies. Rain runoff carries the parasite to surface water supplies. Official estimate that crypto is in about one third of the country's finished drinking water supplies.

The parasite causes severe diarrhea and nausea. Healthy individuals recover in about 10 days, but the virus can be deadly for children, the elderly or anyone with a weak immune system, such as those affected by AIDS.

Besides cypto, other parasites of concern include:


Typhoid Fever: Diarrhea. severe vomiting enlarged spleen,inflamed; often fatal if untreated
  • Cholera: Diarrhea, severe vomiting dehydration often fatal if untreated
  • Bacterial dysentery: Diarrhea; rarely fatal except in infants without proper treatment
  • Enteritis: Severe stomach pain, nausea, vomiting; rarely fatal

    Bacterial Diseases

    Other major bacterial diseases frequently linked to consumption of drinking water are caused by Shigella spp., Salmonella spp., pathogenic E. coli, and Campylobacter spp. All have multiple routes of infection and may be transmitted through water, food, soil, or person-to-person contact. However, in each case, major outbreaks of these diseases have been linked to consumption of contaminated water. Morris and Levin (2) have estimated that within the United States,contaminated water is responsible for 35,000 cases of shigellosis, 59,000 cases of salmonellosis, 150,000 cases of infection with pathogenic E. coli, and 320,000 cases of campylobacteriosis.


  • Infectious Hepatitis:Fever, severe headache loss of appetite abdominal pain, jaundice enlarged liver rarely fatal but may cause permanent liver damage
  • Polio: High fever severe headache sore throat, stiff neck, deep muscle pain, severe weakness, tremors, paralysis in legs, arms, and body; can be fatal

    In many ways, viruses are the most poorly understood area of research on waterborne disease. A number of authors have suggested that Norwalk virus and Norwalk-like viruses are the major causes of both food- and waterborne illnesses worldwide (143).

    There is also strong epidemiologic evidence that hepatitis A (HAV) and rotaviruses are frequent causes of waterborne disease (147). HAV is reported to be the first virus definitively shown to be transmitted by water, and numerous outbreaks have been documented .HAV is one of the most prevalent waterborne viral pathogens. Rotaviruses are also frequently reported in outbreaks and, together with enteroviruses, have been isolated from chlorinated drinking water systems (149,150). These viruses are a primary cause of traveler's diarrhea. They are also a major cause of infantile gastroenteritis and have been reported to be responsible for 50% of hospitalized cases of diarrheal illness in temperate climates (148,151).

    Bennett et al.'s analysis (84) suggested that 300,000 cases of waterborne infection were caused annually by Norwalk virus in the United States. Rose and Gerba's 1986 review of viruses in treated drinking water (148) listed more than 110 types of enteric viruses capable of environmental transmission. Morris and Levin (2) provide a point estimate of 6.5 million annual cases of waterborne viral disease in the United States, with an estimated mortality of 0.005%. As previously discussed, many assumptions necessarily made in these estimates may dramatically underestimate or overestimate burden of disease.

Parasitic protozoa:

  • Amoebic dysentery: Severe diarrhea, headache, abdominal pain, chills fever; if not treated can cause liver abscess, bowel perforation and death
  • Giardia ( now fairly common in US) Diarrhea, abdominal cramps flatulence belching, fatigue. Increasing number of pets are picking up this parasite as well as humans..


  • Cryptosporidium parvum oocysts and Giardia lamblia (intestinalis) cysts imaged together for purposes of comparison. In the photomicrograph, the C. parvum oocysts are distinguished from neighboring G. lamblia cysts by their smaller size. Bar = 10 microns.

Protozoan Diseases

G. lamblia and C. parvum

Smith and Lloyd (111) have recently reported that these two protozoa are responsible for more than 600 million infections worldwide, of which a significant proportion are waterborne. For example, 60% of Giardia cases are estimated to be waterborne in the United States (84), with a point estimate of the annual incidence of giardiasis of 260,000 cases (2). Until recently, giardiasis was the most frequently reported waterborne disease (112,113). Cryptosporidiosis has now overtaken giardiasis, with a point estimate of 420,000 annual waterborne cases in the United States (2).

Over the past 10 years, there has been considerable emphasis on C. parvum research. This is partly because of the scale of waterborne outbreaks seen in 1989 (116) (estimated 13,000 cases) and again in 1993 (117) (estimated >400,000 cases) but also because the outbreaks were associated with filtered water supplies apparently meeting all appropriate standards for that time.

Cryptosporidiosis Outbreaks are reported with increasing frequency not only in the United States (116-118) but also globally in both developed (119,120) and developing countries (121,122). It is probable that reporting of cryptosporidiosis infections will increase dramatically as awareness of this disease increases.

Seroprevalence studies indicate that exposure to C. parvum is widespread and that asymptomatic infection occurs frequently. In a study of 803 children in Oklahoma, 13% of children under 5 years of age, 38% of children 5 to 13 years of age, and 58% of adolescents 14 to 21 years of age were seropositive (123).

Considerable research has been directed toward understanding the etiology of cryptosporidiosis, in particular, its transmission from animal host through the water supply to the human host. As with Giardia and many of the other pathogens described in this review, C. parvum has a broad host range, making elimination of this pathogen from the watershed virtually impossible. Both Giardia cysts and infectious C. parvum oocysts recently have been shown to be disseminated by waterfowl (125).

Parasitic worms:

  • Schistosomiasis: Abdominal pain, skin rash, anemia, chronic fatigue, and chronic general ill health

Algal blooms:

  • "Recently, considerable interest has been focused on the plant plankton genus called Pseudonitzchia, diatoms in which some species produce domoic acid, a potent neurotoxin which causes short-term memory loss and death.

    Toxic varieties of this Pseudonitzchia were first discovered in 1987 when people who had eaten mussels on Prince Edward Island in Canada began experiencing short-term memory loss. Since that time another toxic species of this genus, P. australis, was found to be responsible for the death of pelicans off the California coast. Psuedonitzschia has also been found in New England waters where health officials now monitor the mussels for the presence of the toxin, domoic acid."

    Locally we are dealing with Pfeisteria:

  • Human Health Impacts Thirteen people who worked with dilute toxic cultures of Pfiesteria sustained mild to serious adverse health impacts through water contact or by inhaling toxic aerosols from the cultures.   

    The effects include a suite of symptoms such as narcosis (a "drugged"effect), development of sores (in areas that directly contact water containing toxic cultures of P. Piscicida, and also on the chest and face), uniform reddening of the eyes, severe headaches, blurred vision, nausea/vomiting, sustained difficulty breathing (asthma-like effects), kidney and liver dysfunction, acute short-term memory loss, and severe cognitive impairment (= serious difficulty in being able to read, remember one's name, dial a telephone number, or do simple arithmetic beyond 1 + 2 = 3).Most of the acute symptoms proved reversible over time, provided that the affected people were not allowed near the toxic cultures again.    Some of these effects have recurred (relapsed) in people following strenuous exercise, thus far up to six years after exposure to these toxic fish-killing cultures.   


In LDC countries, simple techniques such as drinking water which has been stored in plastic bottles, whose bottoms were painted black, and exposed to intense sunlight for at least five minutes is enough to kill most of the parasites in the water.

Cultural practices, which encourage people to share their water supplies with domestic animals or to use the same water supplies for drinking and waste increases diseases transmission. Here better education can have a major impact.

Funding or help for towns to build wells for drinking water may be more important than expensive water treatment plants. Estimated costs of $500-1000 per village well is enough to significantly reduce infant/child mortality.

In MDC ( more developed countries) upgrading their old, antique water purifications centers, better training of personnel in this centers, and decreasing nutrients which come from fertilization of fields, domestic animal production centers ( especially chicken, hog) would all help reduce disease transmission.


Return to introduction 1. Go to sediments 2. Go to inorganics: 3. Go to disease vectors 4. Go to plant nutrients: 5. Got to organics 6. Go to Oxygen-demanding wastes 7. Go to radioactive & thermal wastes