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Cryptosporidium is a protozoan pathogen of the Phylum Apicomplexa and causes a diarrheal illness called cryptosporidiosis. Other apicomplexan pathogens include the malaria parasite, Plasmodium, and Toxoplasma, the causitive 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 feces 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 such as AIDS patients. 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 oocyst can survive for lengthy periods outside a host and resists many common disinfectants, notably chlorine based disinfectants. Because of this resistance, water purification to eliminate Cryptosporidium generally relies upon coagulation followed by filtration or boiling. Recently, it has been discovered that the Cryptosporidium reproductive cycle can be inhibited with ultraviolet light, or by ozonation, and water treatments based on these sterilization methods are being evaluated.
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 *.
Life cycle
Cryptosporidium has a spore phase (oocyst) and in this state can survive for lengthy periods outside a host and also resist many common disinfectants, notably chlorine-based disinfectants. Because of this resistance, water treatment 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 water treatment based on this is being developed. [http://www.awwarf.org/research/TopicsAndProjects/topicSnapshot.aspx?topic=uv
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, membranes, and bag and cartridge filters. Conventional, direct, slow sand and diatomaceous earth technologies will remove 99% of Cryptosporidium. 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.
A significant outbreak of Cryptosporidium occurred in April 1993, when 403,000 people in Milwaukee, Wisconsin - approximately one quarter of its population - were sickened by one of its two water treatment plants producing contaminated water. See: Milwaukee Cryptosporidium outbreak.
Reference
- A. Clinton White Jr. Cryptosporidiosis. in Principles and Practice of Infectious Diseases, 6th Ed. G Mandell, J Bennett, R Dolin Eds. Elsevier, 2005. Pages 3215-28.
"Cryptosporidium"