Cryptosporidium hominis and Cryptosporidium parvum belong to the family of Cryptosporidiidae, unicellular parasites that cause the clinically manifested diarrhoea disease cryptosporidiosis. Species such as C. canis or C. felis seldomly infect humans. In particular, livestock such as cattle, horses and goats as well as domestic animals including dogs, cats and birds are regarded as sources and hosts of zoonotic cryptosporidia. Infections with C. hominis originate exclusively from humans themselves. First recorded as a human pathogen in 1976, cryptosporidia can currently be detected in the faeces in two to four percent of diarrhoeal patients in industrialised countries. The pathogen forms four to six micrometre (μm) large oocysts – a microscopically visible stage in the life cycle of parasitic protozoa – which are then excreted by the host. The sporozoites – the infectious developmental stage of the parasites – are then responsible for an infection.
The transmission of Cryptosporidium from human to human and from animal to human occurs mainly through contaminated water or food. Cryptosporidia are intestinal parasites that, after excretion by the host, enter the body via food intake or faecal-oral transmission. The dose of oocysts needed to trigger an infection is very low – only ten to 1,000 are sufficient. In 1993, a cryptosporidiosis outbreak caused by contaminated drinking water infected about 400,000 people in Milwaukee, Wisconsin, USA.
After the absorption of oocysts, the sporozoites are released in the small intestine of the affected person. A complex reproduction process leads to the formation of thick-walled and thin-walled oocysts. The thick-walled oocysts are excreted again via the faeces, the thin-walled variations release further sporozoites and can cause autoinfections in the entire gastrointestinal tract. After an incubation period of about one to twelve days, symptoms including watery diarrhoea, substantial fluid loss, abdominal pain, nausea, fever and weight loss can occur. But asymptomatic infections are also possible. The symptoms subside after a maximum of two weeks. Only in rare, extreme cases can cryptosporidiosis lead to secondary sclerosing cholangitis (inflammation of the bile ducts), pancreatitis or death.
For inpatient accommodation, affected persons should use separate sanitary facilities and they should be accommodated separately from immunosuppressed patients. In addition, standard hygiene measures should be used in hospitals and outpatient areas, including consistent hand hygiene. Detection of human pathogenic Cryptosporidium spp. – as far as it indicates an acute infection – must be reported in Germany.
The excreted thick-walled oocysts are very resistant to environmental influences such as heat or cold. In a humid environment, they are able to remain infectious for months, in rare cases, for up to two years.
Special disinfectants with proven efficacy for parasites are required.