Along the California coast and Channel Islands an unusual mortality event (UME) occurred between 2013–2017 in California sea lions (Zalophus californianus) as a result of climate change-related weather patterns and associated alterations in prey availability. This caused a large number of animals, especially juveniles, to strand along the coast suffering primarily from malnutrition. Pathological findings during that period showed an increase in prevalence of parasitic rhinitis in California sea lions and Northern elephant seal pups (Mirounga angustirostris) that died during rehabilitation at the Marine Mammal Center Los Angeles, San Pedro, CA. All three previously reported nasal mite species were found in the nasal passages and the upper respiratory tract: Orthohalarachne attenuata and O. diminuata in California Sea Lions, and Halarchne halichori in Northern elephant seals.^3,4,5,6 While previous reports did not find association with the clinical disease, our detailed gross and histopathological findings indicate that animals with a heavy parasitic load present with significant pathologic lesions such as severe mucopurulent rhinitis that may impact clinical presentation and overall health.^5,8 An increase in number of animals affected and in the severity of Orthohalarachne attenuata infestation was observed over the four year period (2013–2017). An interesting new trend in this population is the parasitic stage and age of the affected animals. Previous studies described the prevalence of predominantly parasitic larvae in older pinnipeds, while our study showed mostly adult parasite infestation in pups and juvenile pinnipeds.^1,2,7,8,9 Since many of these animals are the ones surviving UME, the question is if the pup has been infected for a longer period of time allowing the parasite to mature. This shift of parasitic life stage and the age of the affected pinnipeds is particularly puzzling and may be related to the immunocompromised status of the juvenile animal affected by malnutrition during an UME or a prolonged stunted growth afterwards. Further studies are needed to look deeper into the epidemiology and clinical relevance of parasitic rhinitis among stranded pinnipeds, morphology and life cycle of the parasite, and to compile the data for the comparison of findings among species and age groups within each species across the West Coast. It would also be of interest to study the nasal mites’ role as a potential vector for infectious diseases in pinnipeds.

Acknowledgment

This work is approved by NOAA and supported by the intramural summer student research grant by Western University of Health Sciences.

* Presenting author

Literature Cited

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