Organism Cryptosporidium parvum is a protozoan parasite found in poultry, fish, reptiles and mammals, especially cattle, pigs, sheep, dogs and cats, from which the infection can be acquired.

Clinical features Cryptosporidiosis presents as an acute watery diarrhoea associated with abdominal pain. Fever, anorexia, nausea and vomiting can also occur, especially in children. There may be repeat attacks, but these do not normally continue for more than a month. In the immunodefi-cient, especially those with HIV infection, the disease enters a chronic and progressive course.

Diagnosis is by finding the oocyst in faecal samples. Alternatively, the intestinal stages can be looked for in intestinal biopsy specimens.

Transmission is from person-to-person via the faecal-oral route, from animals or faecal-contaminated water. The oocyst can survive in nature for a considerable period of time. The infecting dose is very low.

Incubation period. 1-12 days. Mean of 7 days.

Period of communicability Up to 6 months in faecal material.

Occurrence and distribution. Cryptosporidiosis has a worldwide distribution, found particularly in conditions of poor hygiene. It is endemic in many developing countries where infection is acquired at an early age. Massive epidemics have occurred in developed countries when the water purification system had failed (such as the 1993 Milwaukee epidemic where there were 500,000 cases). In other areas, it is a disease of animal handlers, homosexuals and institutions. There is a marked seasonality in the northern hemisphere with peaks of disease in spring and autumn.

Control and prevention is by personal hygiene, the provision of sanitation and safe water supplies. Domestic animals and pets can be important sources of infection and therefore precautions should be taken when handling them.

Treatment is with oral rehydration to replace fluid loss (Section 8.1).

Surveillance Animals, particularly cattle and pigs, can be examined for Cryptosporidium infection.

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