Branching network of proteinaceous filaments within the parasitophorous vacuole of Encephalitozoon cuniculi and Encephalitozoon hellem.

The microsporidia are a diverse phylum of obligate intracellular parasites that infect all major animal groups and have been recognized as emerging human pathogens for which few chemotherapeutic options currently exist. These organisms infect every tissue and organ system, causing significant pathology, especially in immune-compromised populations. The microsporidian spore employs a unique infection strategy in which its contents are delivered into a host cell via the polar tube, an organelle that lies coiled within the resting spore but erupts with a force sufficient to pierce the plasma membrane of its host cell.