Isosporiasis

Isosporiasis (cystoisosporiasis) is intestinal infection by Cystoisospora belli, acquired by swallowing mature oocysts in food or water contaminated with faeces. It is found in tropical and subtropical areas and is an AIDS defining illness in people with HIV.

• Oocysts mature outside the body in 1 to 2 days.
• Chronic diarrhoea with weight loss is typical in HIV.

Watery, non bloody diarrhoea, cramps, nausea, anorexia, malaise, low grade fever and weight loss; steatorrhoea may occur.

• Self limiting in the immunocompetent (1 to 2 weeks); chronic and relapsing in HIV, with severe dehydration.
• Peripheral eosinophilia is a clue (unusual in other protozoal infections).
• Differential diagnosis: cryptosporidiosis, cyclosporiasis, giardiasis, microsporidiosis, bacterial enteritis, CMV, Mycobacterium avium complex, HIV enteropathy, tropical sprue.
• Complications: dehydration, malabsorption, wasting, extra intestinal spread (lymph nodes, liver, spleen), relapse, death.

Demonstration of oocysts in stool.

• Large elongated oocysts (20 to 30 micrometres) in fresh stool on wet mount; modified acid fast stain; UV autofluorescence; examine repeated samples; PCR.
• Small bowel biopsy shows villous atrophy with parasites; full blood count (eosinophilia).
• HIV test and CD4, electrolytes, albumin.

Cotrimoxazole treatment and secondary prophylaxis.

• Supportive: oral rehydration solution and IV fluids, zinc 20 mg daily in children for 10 to 14 days, nutrition, hand washing, safe water and food.
• Pharmacological: cotrimoxazole 960 mg four times daily for 10 days, then 960 mg twice daily for 3 weeks (immunocompromised), or twice daily for 7 to 10 days (immunocompetent); children trimethoprim 5 mg/kg twice daily. Secondary prophylaxis in HIV: cotrimoxazole 960 mg three times weekly (or daily) until CD4 is over 200 for 6 months. Sulfonamide allergy: ciprofloxacin 500 mg twice daily for 7 days, or pyrimethamine 50 to 75 mg daily with folinic acid 10 to 25 mg daily. Antiretroviral therapy with tenofovir, lamivudine and dolutegravir.
• Procedures: none.
• Special groups: pregnancy, cotrimoxazole with folic acid 5 mg daily; children, weight based dosing; HIV, long courses and prophylaxis; sulfonamide allergy, desensitisation or ciprofloxacin.
• Red flags: severe dehydration, weight loss over 10 percent, persistent diarrhoea, relapse, rash on cotrimoxazole.
• Follow-up: review at 1 week; stool re-examination at 2 weeks; CD4 and viral load monitoring.