Cryptosporidium Infection

Organism

Cryptosporidium is a single celled parasitic organism causing acute diarrhoea. In immunosuppressed patients, in particular HIV infected individuals, it can cause chronic intractable diarrhoea.

Mode of Transmission

Cryptosporidium can be transmitted in several ways. Humans can become infected after eating or drinking food or water contaminated with infected faeces. Direct contact with infected individuals, or clothing or nappies contaminated with diarrhoea, can transmit infection. Domestic animals, particularly sheep and cattle, act as a reservoir for infection, and can spread infection through either direct contact with humans or by food or water contaminated with their faeces. Patients with Cryptosporidium diarrhoea are infectious for several weeks after their diarrhoea resolves, and the organism can survive for up to several months in the environment. Outbreaks have occurred in association with swimming pools and water slides, and also in elderly residential care homes and children's nurseries. Homosexual men are also at particular risk.

Regions Affected

Cryptosporidium has been found throughout the world, but is more prevalent in developing regions.

Prevention

As with all infections transmitted via contamination of food, water or the environment with infected faeces, personal hygiene is important. Hand washing is particularly important after contact with animals, especially those with diarrhoea, and after changing children's nappies or disposing of clothing or bed linen contaminated with faeces. Providing adequate sanitation is also important. Individuals who are at particular risk of severe Cryptosporidium infection should be advised to boil drinking water for a minute, or filter water with a very fine filter.

Immunisation

There is no effective vaccine currently.

Symptoms

The incubation period is usually a week (range 5-28 days). Patients present with acute onset, profuse watery non-bloody diarrhoea, associated with cramping abdominal pains. Nausea and vomiting may occur, particularly in children. Fever is uncommon. The illness generally resolves within 3 weeks, but may be protracted even in patients with normal immunity. In patients with impaired immunity, the diarrhoea is prolonged and severe, resulting in weight loss and malnutrition and contributing to death.

Signs

Patients may be dehydrated and may have some abdominal tenderness, but generally examination is unremarkable.

Tests

The infection is diagnosed by finding Cryptosporidium oocysts (eggs) in fresh faecal samples. Antibody tests may be useful in outbreaks.

Treatment

No treatment, other than rehydration where appropriate, is necessary in patients with normal immunity. Various antibiotics have been tried in immunosuppressed patients, but none is particularly effective. In patients with HIV infection, Cryptosporidium diarrhoea is best treated by boosting their immune system using anti-HIV drugs.

Complications/Outcome

Cryptosporidium infection generally causes mild illness in patients with normal immunity, with no complications. If the individual is immunosuppressed, the infection can result in severe intractable diarrhoea with weight loss and malnutrition. Cryptosporidial infection in patients with impaired immunity may occasionally be complicated by bowel perforation. In HIV infected individuals, prior to the development of anti-HIV drugs Cryptosporidium infection frequently contributed to early death. In recent years, with the advent of anti-HIV drugs, Cryptosporidium diarrhoea is less of a problem in this group.

By Dr Ann Chapman