EXPERIMENTAL TRANSMISSION OF OTOSTRONGYLUS-CIRCUMLITUS (RAILLIET, 1899) (METASTRONGYLOIDEA, CRENOSOMATIDAE), A LUNGWORM OF SEALS IN EASTERNARCTIC CANADA

The transmission of few metastrongyloids infesting marine mammals is k nown. The results of experimental infections using Otostrongylus circu mlitus (Crenosomatidae), a lungworm of pinnipeds, suggested that this metastrongyloid uses fish as intermediate hosts. Various marine organi sms (crustaceans, molluscs, and fish) were exposed to first-stage larv ae from naturally infected young-of-the-year ringed seals (Phoca hispi da) from northern Quebec (Salluit). The first and second moults occurr ed 3 and 56 days post exposure in the mucosa and muscularis of the int estine of American plaice (Hippoglossoides platessoides) kept at 4 deg rees C. Third-stage larvae were found under the intestinal serosa. Att empts to infect invertebrates were unsuccessful. Transmission to seals may occur from mid-June through the autumn as young seals start feedi ng intensively on invertebrates and fish. First-stage larvae leave the lungs via the bronchial escalator and are swallowed and released into the sea with the faeces of seals, where they would be available to be nthic or pelagic fish. The morphology of the first three larval stages is described.