Morphological and molecular characterization of Encephalitozoon hellem in hummingbirds

Microsporidiosis was identified as a cause of enteritis in wild, migratory hummingbirds (Calypte anna). Electron microscopic examinations of parasites showed microsporidian spores with a double spore coat and a polar filament containing four to six coils, compatible with the genus Encephalitozoon. Molecular analysis of ribosomal RNA genes further identified the parasites from droppings and small intestinal segments as Encephalitozoon hellem, genotype I. Microsporidial spores were identified in 19% of droppings from C. anna, Archilochus alexandri and Selasporus sasin using Gram or modified trichrome staining methods. Since E. hellem is an opportunistic pathogen in immunocompromised humans, the pathogenic potential in avian hosts, the zoonotic potential of this parasite, and the role of birds as reservoirs needs to be further explored.