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Cryptosporidium is a protozoan that is often associated with diarrhea in humans.

General characteristics

Cryptosporidium is a protozoan pathogen of the Phylum Apicomplexa and causes a diarrhoeal illness called cryptosporidiosis. Other apicomplexan pathogens include the malaria parasite Plasmodium, and Toxoplasma, the causative agent of toxoplasmosis. Unlike Plasmodium, which transmits via a mosquito vector, Cryptosporidium does not utilize an insect vector and is capable of completing its life cycle within a single host, resulting in cyst stages which are excreted in faeces and are capable of transmission to a new host.

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.

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.

Cryptosporidiosis is typically an acute short-term infection but can become severe and non-resolving in children and immunocompromised individuals. 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.

The genome of Cryptosporidium parvum was sequenced in 2004 and was found to be unusual amongst Eukaryotes in that the mitochondria seem not to contain DNA ^[1]. A closely-related species, C. hominis, also has its genome sequence available ^[2]. CryptoDB.org is a NIH-funded database that provides access to the Cryptosporidium genomics data sets.

Life cycle

Life cycle of Cryptosporidium spp.

Cryptosporidium has a spore phase (oocyst) and in this state it can survive for lengthy periods outside a host. It can also resist many common disinfectants, notably chlorine based disinfectants.^[3] As a result of this resistance, water purification to eliminate Cryptosporidium generally relies upon coagulation followed by filtration or boiling. Recently, it has been discovered that Cryptosporidium is sensitive to ultraviolet light and ozonation, and water treatments based on these sterilization methods are being developed.^[4][5]

Treatment of drinking water

Most treatment plants that take raw water from rivers, lakes, and reservoirs for public drinking water production use conventional filtration technologies. This involves a series of processes including coagulation, flocculation, sedimentation, and filtration. Direct filtration, which is typically used to treat water with low particulate levels, includes coagulation and filtration but not sedimentation. Other common filtration processes are slow sand, diatomaceous earth filter, membranes, and bag and cartridge filters. Conventional, direct, slow sand and diatomaceous earth technologies will remove 99% of Cryptosporidium.^[6] Membranes and bag and cartridge filters remove Cryptosporidium on a product-specific basis. With the proper concentrations and contact time, Cryptosporidium inactivation will occur with chlorine dioxide and ozone treatment. Additionally, ultraviolet light treatment at relatively low doses will inactivate Cryptosporidium.

Exposure risks

The following groups have an elevated risk of being exposed to Cryptosporidium:

• Child care workers
• Parents of infected children
• People who take care of other people with cryptosporidiosis
• International travelers
• Backpackers, hikers, and campers who drink unfiltered, untreated water
• People, including swimmers, who swallow water from contaminated sources
• People who handle infected cattle
• People exposed to human feces through sexual contact

Cases of cryptosporidiosis can occur in a city that does not have a contaminated water supply. In a city with clean water, it may be that cases of cryptosporidiosis have different origins. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. Note that cryptosporidium typically does not cause serious illness in healthy people. It may chronically sicken some children, as well as adults who are exposed and immunocompromised. A subset of the immunocompromised population is people with AIDS. Some sexual behaviors can transmit the parasite directly.

Trivia

In the Destroy All Humans! video-games series, the main character is called Cryptosporidium. A reference to the named organism in this article.

References

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• White, A. Clinton, Jr. "Cryptosporidiosis". In Mandell, G et al, eds., Principles and Practice of Infectious Diseases, 6th edition; Elsevier, 2005, pp 3215-28.

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External Links

• CryptoDB: The Cryptosporidium Genome Resource
• Boil Check: Postcode check for contaminated water areas