Experimental transmission of Pharurus pallasii (Nematoda: Metastrongyloidea), a lungworm of the cranial sinuses of the beluga whale (Delphinapterus leucas), to fish

Transmission of lungworms (Metastrongyloidea: Pseudaliidae) in the marine environment has been poorly studied. This experimental study is the first conducted on a pseudaliid, Pharurus pallasii, a lungworm of the cranial sinuses of the beluga whale (Delphinapterus leucas). First-stage larvae removed from uteri of gravid female P pallasii from a freshly dead beluga were experimentally exposed to various marine organisms (fish, crustaceans, molluscs). First-stage larvae failed to develop in experimentally exposed invertebrates. The first moult occurred in the intestinal wall of American plaice (Hippoglossoides platessoides) and Arctic sculpins (Myoxocephalus scorpioides) 45 and 78 days post exposure, respectively. The third larval stage, which is infectious to the final host, was not observed in fish during the 14 months of the experiment. No cellular inflammatory reaction to or encapsulation of larvae was observed in histological sections of the intestinal wall of American plaice 268 days post exposure. Survival and development of P. pallasii larvae to the second stage in fish suggest that fish are likely suitable intermediate hosts in the life cycle of P. pallasii. Invertebrates may still play a role as transport (paratenic) hosts. The morphology of the first and second larval stages of P. pallasii is described for the first time.