[krip-toh-spawr-i-dahy-oh-sis, ‐spohr‐]
Cryptosporidiosis is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection. It is spread through the fecal-oral route; the main symptom is self-limiting diarrhea in people with intact immune systems. In immunocompromised individuals, such as AIDS patients, infection can cause permanent and life-threatening explosive diarrhea also known as "the Bangkok Blast" or the "Thai Fourth of July". Despite not being identified until 1976, it is one of the most common waterborne diseases and is found worldwide. The parasite is transmitted by environmentally hardy cysts (oocysts) that, once ingested, excyst in the small intestine and result in an infection of intestinal epithelial tissue.


Infection is through contaminated material such as earth, water, uncooked or cross-contaminated food that has been in contact with the feces of an infected individual or animal. Contact must then be transferred to the mouth and swallowed. It is especially prevalent amongst those in regular contact with bodies of fresh water, whether through work or recreation. The source can be recreational water like swimming pools, contaminated water supplies, or contaminated food. Vacationers must be particularly careful about contamination. The high resistance of Cryptosporidium oocysts to disinfectants like chlorine bleach facilitates transmission of the disease. Some outbreaks have happened in day care related to diaper changes.


Symptoms appear from two to ten days after infection and last for up to two weeks. As well as watery diarrhea, there is often stomach pains or cramps and a low fever. Some individuals are asymptomatic (have no symptoms) but are nevertheless infective, and thus can pass on the infection to others. Even after symptoms have finally subsided an individual is still infective for some weeks. Severe diseases, including pancreatitis, can occur.

Treatment is primarily supportive. Fluids need to be replaced orally. A lactose free diet should be taken as tolerated. In rare situations, intravenous fluids may be required. Antibiotics are not usually helpful, and are primarily reserved for persons with severe disease and a weak immune system. Sometimes relapses happen.

Prevention is through washing hands carefully after going to the bathroom or contacting stool, and before eating. If safety of the water supply is questionable, it can be boiled. It is not necessary to boil water for lengthy periods e.g. 15 minutes: simply bringing the water to the boil will kill any cryptosporidium oocysts in it. Suspect water supplies can also be carefully filtered before drinking, though boiling water is easier and requires no special equipment.


There is no reliable treatment for cryptosporidium enteritis -- certain agents such as paromomycin, atovaquone, nitazoxanide, and azithromycin are sometimes used but they usually have only temporary effects. Currently, the best approach is to improve the immune status in immunodeficient individuals. The probiotic Saccharomyces boulardii sold over the counter in pharmacies and health shops (Brand name Florastor in US and DiarSafe in UK) has been found to be a helpful natural treatment in managing diarrhoea of various infectious origins including cryptosporidium.

The majority of immuno-competent individuals suffer a short (less than 2 weeks) self limiting course that requires supportive care with re-hydration and occasionally anti-diarrhoeal medication. In immuno-incompetent individuals (including some with HIV/AIDS) anti-retroviral therapy has been associated with improved outcomes. Several drug trials with high dose azithromycin look promising.

Infectious agents

A number of species of Cryptosporidium infect mammals. In humans the main causes of disease are C. parvum and C. hominis (previously C. parvum genotype 1). C. canis, C. felis, C. meleagridis, and C. muris can also cause disease in humans.

Non-human examples

The most important zoonotic reservoirs are cattle, sheep and goats. Additionally, in recent years, cryptosporidiosis has plagued many commercial Leopard gecko breeders. Several species of the Cryptosporidium family (C. serpentes and others) are involved, and outside of geckos it has been found in monitor lizards, iguanas, tortoises as well as several snake species.

Notable cases

  • In 1993, a waterborne cryptosporidiosis outbreak occurred in Milwaukee, Wisconsin. An estimated 403,000 people became ill, including 4,400 people hospitalized.
  • The UK's biggest outbreak occurred in Torbay in Devon in 1995 when 575 people fell ill.
  • In the summer of 1996, cryptosporidium affected approximately 2,000 people in Cranbrook, British Columbia, Canada. Weeks later, a separate incident occurred in Kelowna, British Columbia where 10,000 to 15,000 people got sick.
  • In April of 2001, an outbreak occurred in the city of North Battleford, Saskatchewan, Canada. Between 5800 and 7100 people suffered from diarrheal illness, and 1907 cases of cryptosporidiosis were confirmed. Equipment failures at the city's antiquated water filtration plant following maintenance were found to have caused the outbreak.
  • In the summer of 2005, after numerous reports by patrons of gastrointestinal upset, a water park at Seneca Lake State Park, in the Finger Lakes region of upstate New York, was found to have two water storage tanks infected with Cryptosporidium. By early September 2005, over 3,800 people reported symptoms of a Cryptosporidium infection. The "Sprayground" was ordered closed for the season on August 15.
  • In October 2005 Gwynedd and Anglesey areas of North Wales (UK) suffered an outbreak of Cryptosporidiosis. The outbreak may have been linked to the drinking water supply from Llyn Cwellyn but this is not yet confirmed. As a result, over 200 people fell ill and the company Welsh Water (Dwr Cymru) advised 61000 people to boil their water before use.
  • In March 2007, a suspected outbreak occurred in Galway, Ireland, after the source of water for much of the county, Lough Corrib, was suspected to be contaminated with the parasite. A large population (90,000 people) including areas of both Galway City and County were advised to boil water for drinking, food preparation and for brushing teeth. On 21 March 2007, it was confirmed that the city and county's water supply was contaminated with the parasite. The area's water supply was finally given the all-clear on 20 August, 2007; five months after it was first detected. Around 240 people contracted the disease, however experts say the true figure could range up to 5,000.
  • Hundreds of public pools in 20 Utah counties were closed to young children in 2007, as children under 5 are most likely to spread the disease, especially children wearing diapers. As of September 10, 2007 the Utah State health department had reported 1302 cases of cryptosporidiosis in the year; a more usual number would be 30. On September 25, the pools were re-opened to those not requiring diapers, but hyperchlorination requirements were not lifted.
  • On September 21, 2007, Cryptosporidium outbreak attacked the Western United States: 230 Idaho residents, with hundreds across the Rocky Mountain area; in the Boise and Meridian areas; Utah, 1,600 illnesses; Colorado and other western states - Montana, decrease.
  • On 25 June, 2008, Cryptosporidium was found in water supplies in Northampton, Daventry and some surrounding areas supplied from the Pitsford Reservoir as reported on the BBC People in the affected areas were warned not to drink tap water unless it had been boiled. Anglian Water confirmed that 108,000 households were affected, the equivalent of some 250,000 consumers. They advised that water may not be fit for human consumption for many weeks. The boil notice was lifted for all the affected customers on 4 July, 2008.
  • Throughout the Summer of 2008; many public swimming areas, water parks, and public pools in the Dallas/Fort Worth Metroplex of Texas suffered an outbreak of Cryptosporidiosis. Burger's Lake in Fort Worth was the first to report such an outbreak. This prompted some if not all city-owned & private pools to close and hyperchlorinate. To date, there have been 400 reported cases of Cryptosporidium
  • A gym in Cambridge, UK was forced to close its swimming pool until further notice after health inspectors found an outbreak of cryptosporidiosis. Environmental Health authorities requested that the water be tested after it was confirmed that a young man had been infected.
  • 1998 Sydney water crisis
  • 2002 Glasgow floods
  • Cryptosporidium in Galway
  • Milwaukee Cryptosporidium outbreak


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