Identification of the microsporidian parasite, Enterocytozoon bieneusi in faecal samples and intestinal biopsies from an AIDS patient.

The microsporidian parasite, Enterocytozoon bieneusi, is currently recognized as a potentially important cause of chronic diarrhoea in patients infected with the human immunodeficiency virus (HIV). Faecal concentrates from a 38-year-old, HIV-seropositive patient examined by light and electron microscopy revealed the presence of numerous microsporidian spores. The structural characteristics of the spores were consistent with those previously described for Enterocytozoon bieneusi. Each spore contained a single nucleus, a posterior vacuole and a polar filament with 6-7 overlapping coils which appeared in cross-section as a series of 3 doublets. Mature spores were surrounded by an inner unit membrane, an electron-lucent endospore and a thin, electron-dense exospore. The identity of the parasite was confirmed by the detection of unique endogenous developmental stages in duodenal biopsies. Both proliferative and sporogonial plasmodia (meronts and sporonts) were observed and all stages were monokaryotic (single nucleus) and apansporoblastic (sporophorous vesicle absent). Proliferative and sporogonial plasmodia divided by plasmotomy and spore organelles (polar filament, attachment disc and polaroplast) were well developed prior to fission of the sporogonial plasmodium.