Isospora belli is a parasite which belongs to the Coccidia family, which also include Cryptosporidium and Toxoplasma gondii. It is most commonly found in tropical and subtropical climates.

It is probably transmitted by oral-faecal contact from person-to-person and by drinking water contaminated by faeces carrying the parasite; unlike Cryptosporidium, it does not appear to be transmitted from animal-to-human. It can infect the intestines of HIV-positive people, causing the illness known as isosporiasis (sometimes called coccidiosis).

Symptoms and diagnosis

Isosporiasis causes symptoms very similar to those of cryptosporidiosis watery diarrhoea, cramping pains in the abdomen and weight loss.

It is diagnosed by testing a sample of stool (faeces) for the presence of the parasite.

Treatment

Co-trimoxazole (one double-strength tablet 4 times a day for 10 days, then twice a day for 3 weeks) is effective against isosporiasis; the diarrhoea usually improves within a couple of days of starting treatment. It also has a preventive effect, so people who are receiving co-trimoxazole as PCP prophylaxis are at low risk of developing isosporiasis.

For people who cannot tolerate co-trimoxazole, pyrimethamine plus folinic acid, pyrimethamine plus sulphadoxine, metronidazole or furazolidone may be offered. Maintenance therapy (secondary prophylaxis) with co-trimoxazole, pyrimethamine alone, pyrimethamine plus sulphadoxine or metronidazole is necessary to try to prevent recurrence.

Key research

Pape successfully treated 32 patients with co-trimoxazole (160mg/800mg by mouth four times daily for 10 days). 22 patients were randomized to receive maintenance therapy of either co-trimoxazole (160mg/800mg three times a week) or sulphadoxine-pyrimethamine (500mg/25mg weekly). One patient receiving co-trimoxazole relapsed three weeks after initiation of maintenance. All others remained asymptomatic. 5/10 on placebo relapsed 1.5 months after initial treatment.

Weiss successfully treated two AIDS patients, unable to tolerate sulphonamides, for isosporiasis with pyrimethamine (50-75mg by mouth every day) and folinic acid (10mg by mouth every day); recurrence was prevented by maintenance treatment with pyrimethamine (25mg by mouth every day) and folinic acid (5mg by mouth every day).

Kayembe treated 8 AIDS patients with abdominal pains and Isospora belli diarrhoea with 200mg diclazuril for 7 days. The abdominal pains and cramps disappeared in all 8 patients. All patients were negative for I. belli at the first check up. In 1 patient severe diarrhoea persisted.

References

de Hovitz JA et al. Clinical manifestations of Isospora belli patients with AIDS. NEJM 315: 87-90, 1986.

Kayembe K et al. Diclazuril for Isospora belli infection in AIDS. Lancet i: 1397-1398, 1989.

Pape JW et al. Treatment and prophylaxis of Isospora belli infection in patients with the acquired immune deficiency syndrome. NEJM 320(16): 1044-1047, 1989.

Weiss LM et al. Isospora belli infection: treatment with pyrimethamine. Ann Int Med 109(6): 474-75, 1988.