Microspridiosis is an opportunistic intestinal infection that causes diarrhea and wasting in immunocompromised individuals (HIV, for example). It results from different species of microsporidia, a group of protozoal parasites.
In HIV infected individuals, microsporidiosis generally occurs when CD4+ T cell counts fall below 100.
Food and Water Borne :: Conditions and Diseases

CDC DPDx - Microsporidiosis - Factsheet with causal agents, life cycle, geographic distribution, laboratory diagnosis, and treatment.
Microsporidiosis - Information resources from The Body on this opportunitistic infection.