To date, little information is known about the transmission of parasitic helminths in marine mammal hosts. The literature lists over 260 species of helminths found parasitizing marine mammals and of these only five cycles have been demonstrated.

The only lungworm cycle known to date is that of Parafilaroides decorous from the California Sea Lion (Zalophus californianus) (Dailey, 1970). This cycle demonstrated an adaptation for the larval stage to go directly through a vertebrate intermediate host. However, no prenatal infection is found in this mammalian final host.

This study documents the findings of a study carried out in Florida on T. truncatus calf mortality from 1987 to 1989. Four calves were examined and found infected with lungworm. The largest of these calves measured 134 cm and one had the umbilical cord still attached.

The recovered lungworms were found in both lobes of the lung. These worms were cleared and identified as Holocerus lagenorynchi Baylis and Daubney 1925. Both male and female worms were recovered in large numbers. The male worms had completed spicule development with a fully formed looped gubernaculum which is specific for H. lagenorhynchi. The females contained fully developed larvae in the uterus.

The present findings of prenatal infections with adult H. lagenorhynchi in T. trucatus calves indicates that the transplacental mode of transmission may be more common in cetacean lungworms than suspected previously. Just how many members of the pseudalid family use this type of transmission needs additional observation. However, the evidence presented here suggests the potential for early postnatal loss of large numbers of cetacean calves where verminous pneumonia may develop.

References

1.  Dailey, M.D. 1970. The transmission of Parafilaroides decorus (Nematoda: Metastrongylidae) in the California sea lion (Zalophus californianus). Proceedings of the Helminthological Society of Washington. 37: 215-222.