MODES OF TRANSMISSION OF LOMA-SALMONAE (MICROSPORIDIA)

Loma salmonae (Putz, Hoffman and Dunbar, 1965) Morrison and Sprague, 1 981 (Microsporidia) causes prominent gill disease in pen-reared chinoo k salmon Oncorhynchus tshawytscha in the Pacific Northwest. Transmissi on of the parasite was examined by exposing Pacific salmon Oncorhynchu s spp, to infectious spores by various routes: per os, intraperitoneal , intramuscular, and intravascular injection, by cohabitation with inf ected fish, and by placement of spores directly on the gill. All expos ure methods led to infections except placement of spores on the gill. Putative sporoplasms were visible in epithelial cells of the alimentar y canal within 24 h of per os exposure. L. salmonae may initially infe ct alimentary epithelial cells and then migrate into the lamina propri a to access the blood stream. Positive results obtained by intravascul ar injection suggest that autoinfection from spores of ruptured xenoma s in the endothelium may also occur. The cohabitation experiment demon strates that fish may become infected by spores released from live fis h.