Cryptosporidium: Could It Be In Your Water?
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Cryptosporidium (krip-toe-spor-id-ee-um) is a tiny parasite, a protozoa, which reproduces and causes disease in humans and animals. This parasite has been associated with large outbreaks of human illness in Canada and the U.S. It can be found in the digestive organs and respiratory tract. Even though the organism was first identified early in the 20th century, the disease cryptosporidiosis wasnt identified until 1976. It has caused outbreaks of illness where thousands of people were infected.
There are 6 recognized species of Cryptosporidium but C. parvum is the species of greatest concern to humans and livestock farmers. This parasite has a rapid life cycle, and can reproduce in the intestinal wall within 12 hours.
The life cycle of this parasite occurs within one animal, but consists of several stages. The oocyststage is the infectious stage. The oocyst is approximately 4 µm (= 0.004 mm) in width, but is able to fold over and travel through smaller openings, creating problems with some water filtration systems. Oocysts are released from the intestinal wall into the fecal material of the infected animal or person. Other people become infected after oocysts enter their mouths. This can occur through person-to-person or animal-to-person contact, or by the ingestion of contaminated water or food.
Poor hygiene often leads to infection. Contact with toilets, diapers, dirt, or animal feces are common sources of infection. The ingestion of contaminated water or food is the most publicized route of infection.
Infection in humans may result in diarrhea, abdominal cramps, headaches, nausea, vomiting and a low-grade fever. The initial symptoms can persist and develop into weight loss and dehydration in severe cases.
Not everyone exposed to the protozoa gets sick. The infection may resolve without supportive treatment. This disease often produces no symptoms, but can still be spread to others.
People with a weak immune system are more severely affected. In these cases, symptoms may persist for long periods. Patients undergoing chemotherapy, recent transplant recipients, AIDS patients, the elderly, and young children are at greatest risk of severe disease.
To date, there is no specific treatment for cryptosporidiosis. The treatment is limited to addressing the symptoms of the disease, and making sure the patient doesnt become dehydrated.
The symptoms are similar for animals. Most often, it is young animals that become infected. Calves become infected under 6 weeks of age, and approximately 25% of calves with diarrhea between 5 days to 1 month old are infected with C. parvum. The symptoms of an acute infection include watery, yellow diarrhea (sometimes containing flecks of blood), mild fever, dehydration, and lethargy. The symptoms of a chronic infection include semi-formed stools, little to no fever, and weight loss. Severe infections are associated with younger animals, inadequate colostrum intake, larger herd size, and poor sanitation. The duration of infection can persist for months and can take considerable effort to eliminate from the herd.
Many studies have been done on the prevalence of C. parvum among farm animals worldwide. It appears from these studies, including a 1997 Ontario study that if enough samples of fresh manure are collected over a long enough period, over 50% of the farms will test positive for Cryptosporidium at least once.
Various studies on beef and dairy farms have shown that when large numbers of samples from several farms are analyzed, about a quarter of the total samples have tested positive. Swine herds are also commonly infected. The 1997 Ontario study found about a quarter of all swine manure samples contained Cryptosporidium. It was detected at least once on 18 of the 20 swine farms in the study (Figure 1).
Figure 1. Collecting manure samples in a swine barn during a recent Ontario study.
Although the oocyst shell is thick and resistant to many chemicals such as chlorine, it is susceptible to drying, freezing, and ultraviolet light. Drying appears to kill oocysts in a matter of hours. With 10 or more days of freezing, one study showed that more than 90% of the oocysts were non-infective. However, at temperatures as high as 30°C, oocysts are able to survive for up to 2 weeks. They are soon killed, though, at temperatures over 55°C, typical of composting. One viability study showed that a small percentage of oocysts could survive in surface water up to at least 6 months. Oocysts can survive for several months in typical liquid manure tanks, as demonstrated by a 1999 Ontario study.
Because many North American cities rely on surface water as their main source of drinking water, prevalence of Cryptosporidium is important. A study of western United States surface waters found Cryptosporidium in about ¾ of the samples. Most of the studies show that between 25% and 75% of surface water samples contain at least a few Cryptosporidium organisms. Wild animals (e.g. raccoons, deer, mice) are known to carry Cryptosporidium (Figure 2).
Figure 2. Cryptosporidium, from a variety of sources, is often found in surface water.
There are actually quite a few potential sources of Cryptosporidium in the environment. The list of most likely sources includes:
A 1999 Ontario study found significantly higher levels of Cryptosporidium in tile drainage water from livestock watersheds than non-livestock areas (Figure 3). However, there were infective organisms in drainage waters from the non-livestock areas also. Other than the association with livestock watersheds, a larger number of samples may have helped narrow down other significant contributors, and studies continue to be carried out to determine these influences.
Figure 3. Cryptosporidium has been found in tile drainage water, even in watersheds with no livestock.
The best way to prevent infection is to limit contact with feces. Following are specific recommendations.
The best method of control is to limit the fecaloral route of transmission of oocysts between young animals. Since the oocysts are not killed by most disinfectants, emphasis must be on cleanliness and reasonable levels of young livestock density. Below are recommendations for control and for preventing environmental impacts.
Fleming, R., Hocking, D., Fraser, H., and Alves, D. 1999. Extent and magnitude of agricultural sources of Cryptosporidium in surface water. Final report to Agricultural Adaptation Council, Guelph, for the National Soil and Water Conservation Program. Available for download from the Ridgetown College website.
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