Crytosporidium
Life History
Once thought to be rare and host specific, Cryptosporidia is now believed to be one of the top three diarrheal causing pathogens in the world. Cryptosporidia muris was recognized in 1907 by E. E. Tyzer. Since then twenty (20) species of Cryptosporidium have been discovered and named although recently sixteen (16) of those twenty (20) have come under speculation due to recent cross-transmission studies. Cryptosporidia is a protozoan parasite which lives in the intestines and respiratory epitheliums of many types of animals including mammals, birds and reptiles. The disease caused by Cryptosporidia is known as Cryptosporidiosis. Cryptosporidia is found all over the world and is transmitted via fecal oral contact. Usually this is due to water contaminated by animal feces. Infected calves excrete up to 10 billion Cryptosporidium oocysts (infectious stage) per day. The infectious dose in humans is only 10-100. However, contaminated food or direct contact with feces can also cause infection.
Microbial Characteristics
Cryptosporidia are small coccidian spore-forming protazoans. When in oocyst form they are 4-6 um in size.
Disease
Cryptosporidia are encountered and transmitted through fecal oral transmission. Once a host ingests an oocyst, sporozoites are released. The sporozoite then can enter the epithelial cells in the small intestine where it will develop into a trophozoite. Inside of a trophozoite, merozoites begin to form. When released, a merozoite can either infect another epithelial cell or it can evolve into a sexual gamete. These gametes then join to form an oocyst and will be excreted in the feces. While in the host’s body, Cryptosporidia carries out its entire life cycle in the microvilli of the small intestine.
The most common symptom of Cryptosporidiosis is watery diarrhea. Other symptoms include:
- Dehydration
- Weight loss
- Stomach cramps or pain
- Fever
- Nausea
- Vomiting
Some people with Cryptosporidiosis will have no symptoms at all. While the small intestine is the site most commonly affected, Cryptosporidium infections could possibly affect other areas of the digestive or the respiratory tract. (CDC) Symptoms usually begin 2-10 days after becoming infected and last 1-2 weeks on average. In immunocompetent individuals, Cryptosporidiosis is not life threatening. Generally only a single episode of diarrhea takes place lasting less than two weeks. For immunocompromised individuals, the life cycle of the organism can be repeated almost indefinitely and often results in death. This has become an especially large problem in AIDS patients worldwide. There is currently no antimicrobial treatment for the disease. Most people with healthy immune systems will recover without treatment. For people with HIV/AIDS, the drugs used as anti-retroviral therapy to improve immune status will also decrease or eliminate symptoms of cryptosporidiosis. (CDC)
Epidemiology
Cryptosporidia is found worldwide in both developing and highly developed countries. Cryptosporidia can be found in the stool of between 1-3% of people in Europe and North America and in 5-10% of people in Asia and Africa. Despite low prevalence rates in developed countries, Cryptosporidia antibodies are found in 32-58% of adults. The most recent outbreak in the United States occurred in 1993 in Milwaukee, Wisconsin. More than 403,000 people were infected and at least 100 immunocompromised AIDS patients died. Approximately 70% of the cases occurred in HIV infected individuals. It is believed that local dairy herds were the source of the parasite which infected the local water supply. One year later in Las Vegas, Nevada a Cryptosporidia outbreak led to the deaths of 41 AIDS patients.
Prevention
The most common method used to make water safe to consume is through chemical disinfection. Most often chlorine is the disinfectant used to treat drinking water. However, this method does not work against Cryptosporidium. Currently there are no chemical disinfection methods that can be used to treat Cryptosporidia. The best way to prevent Cryptosporidiosis in drinking water is by water filtration. This tends to have a high success rate, but some Cryptosporidium oocysts may still get through the treatment process. The CDC has six recommendations to aid in the prevention ofCryptosporidiosis. They include:
- Practice good hygiene.
- Avoid water that might be contaminated
- If you are unable to avoid using or drinking water that might be contaminated, then you can make the water safe to drink by doing one of the following:
o Heat the water to a rolling boil for at least 1 minute.
o Use a filter that has an absolute pore size of at least 1 micron or one that has been NSF rated for "cyst removal." - Avoid food that may be contaminated.
- Take extra care when traveling.
- Avoid fecal exposure during sexual activity.
Resources
Cryptosoridium and Water: A Public Health Handbook. Atlanta, Georgia: Working Group on Waterborne Cryptosporidiosis
Current, W. Cryptosporidiosis. Clinical Microbiology Reviews. July 1991 p. 325-358
Fayer. R, et al. Cryptosporidium spp. and Cryptosporidiosis. Microbiolical Reviews. Dec. 1986 p. 458-483
Gilson. I, et al. Cryptosporidiosis in Patients with HIV Disease. HIV Newsline. Oct. 1996 Vol. 2 Issue 5
Goodgame, R. Understanding Intestinal Spore Forming Protozoa: Cryptosporidia, Microsporidia, Isospora, and Cyclospora. Annals of Internal Medicine. 1996 Vol. 124, Issue 4 p. 429-441
Tzipori, S. Cryptosporidiosis in Animals and Humans. Microbiological Reviews. Mar. 1983 p. 84-96