Encephalitozoon

Encephalitozoon is a genus of microsporidian parasites, obligate intracellular eukaryotes that infect a broad range of hosts, including humans. They are among the smallest intracellular parasites, producing spores with a distinctive polar tube used to invade host cells. The best-known species are Encephalitozoon cuniculi, Encephalitozoon intestinalis, and Encephalitozoon hellem; other species are described but rarely implicated in human disease.

Hosts and transmission: These parasites have a wide host range. E. cuniculi is classically associated with rabbits but can infect other mammals and humans, especially when immune defenses are compromised. E. intestinalis and E. hellem infect humans, often causing intestinal illness or disseminated infection in immunosuppressed individuals. Transmission occurs mainly through ingestion or inhalation of infectious spores.

Clinical features and disease: In humans, intestinal infection presents with chronic diarrhea, abdominal pain, and malabsorption; disseminated disease can involve kidney, liver, eyes, and central nervous system. In rabbits, E. cuniculi commonly causes neurologic signs such as head tilt, tremors, and uveitis. Disease severity depends on host immune status and spore exposure.

Diagnosis and treatment: Diagnosis relies on tissue or stool staining and microscopy, serology, and molecular methods such as PCR. Histology reveals intracellular spores in host cells; spores are detected with stains such as calcofluor white or Gomori methenamine silver. In humans, albendazole is a common therapy; in animals, treatment options include albendazole or fumagillin and supportive care.

Epidemiology and significance: Encephalitozoon species are worldwide in distribution and represent opportunistic pathogens in people with HIV/AIDS, organ transplant recipients, and other immunocompromised individuals. They can be zoonotic and have been linked to environmental exposure, notably contaminated water or food sources.