Cryptosporidium
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 Cryptosporidium muris oocysts found in human feces.
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Cryptosporidium andersoni |
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhoea in humans.
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[edit] 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.
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.
[edit] Life cycle
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] </ref>
[edit] Treatment of drinking water
Many 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 including slow sand filters, diatomaceous earth filter and membranes will remove 99% of Cryptosporidium.[4] 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.[5][6]
For the end consumer of drinking water believed to be contaminated by Cryptosporidium, the safest option is to boil all water used for drinking.
[edit] Exposure risks
The following groups have an elevated risk of being exposed to Cryptosporidium:[citation needed]
- 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 behaviours can transmit the parasite directly.
[edit] Trivia
In the Destroy All Humans! video-games series, the main character is called Cryptosporidium. A reference to the named organism in this article.
[edit] References
- ^ "Complete Genome Sequence of the Apicomplexan, Cryptosporidium parvum". Science/AAAS. Retrieved on 2007-05-06.
- ^ "The genome of Cryptosporidium hominis".
- ^ "Chlorine Disinfection of Recreational Water for Cryptosporidium parvum". CDC. Retrieved on 2007-05-06.
- ^ "The Interim Enhanced Surface Water Treatment Rule – What Does it Mean to You?" (pdf). USEPA. Retrieved on 2007-05-06.
- ^ "Irreversible UV inactivation of Cryptosporidium spp. despite the presence of UV repair genes.". NCBI PubMed. Retrieved on 2007-05-06.
- ^ "Ultraviolet Disinfection and Treatment". AWWARF.org. Retrieved on 2007-05-06.
- White, A. Clinton, Jr. "Cryptosporidiosis". In Mandell, G et al, eds., Principles and Practice of Infectious Diseases, 6th edition; Elsevier, 2005, pp 3215-28.
- Upton, Steve J. (2003-09-12). "Basic Biology of Cryptosporidium" (Website). Kansas State University: Parasitology Laboratory.
- "The Taxonomicon & Systema Naturae" (Website database). Taxon: Genus Cryptosporidium. Universal Taxonomic Services, Amsterdam, The Netherlands (2000).
