Microsporidiosis: An emerging opportunistic parasitic infection

Microsporidia are obligate intracellular, primitive eukaryotic parasites that infect a diverse array of vertebrate and invertebrate hosts. Phylogenetic studies have demonstrated their close relationship to fungi, though they possess unique structural and genomic features. With approximately 220 genera and 1,700 species identified, they exhibit considerable diversity in host range and pathogenic potential. These organisms are widely distributed across humans, animals, and environmental reservoirs, and are increasingly recognized as clinically significant pathogens. They are particularly associated with disease in immunocompromised populations, such as those with advanced HIV infection, organ or bone marrow transplant recipients, and individuals receiving immunomodulatory therapies. However, recent reports have also documented infections in immunocompetent individuals, emphasizing their growing clinical relevance. The clinical manifestations of microsporidiosis are heterogeneous, ranging from chronic gastrointestinal illness to ocular, respiratory, and systemic involvement. Diagnosis primarily relies on microscopic detection of spores in clinical specimens like stool and body fluids. Advanced methods such as molecular assays, immunofluorescence, and electron microscopy enable species-level identification. Therapeutically, albendazole is effective against many microsporidial species, particularly those belonging to the genus Encephalitozoon . However, species such as Enterocytozoon bieneusi and Vittaforma often respond poorly. Effective management depends on early recognition, improved access to diagnostics, and restoration of immune function. Intensified research into host–pathogen interactions and treatment modalities is essential to address the growing burden of microsporidiosis. This review highlights the emerging significance of microsporidia as opportunistic pathogens, emphasizing their epidemiology, host interactions, diagnostic strategies, and current therapeutic challenges in both immunocompromised and immunocompetent populations.