Abstract

Infection with the protozoal parasites Sarcocystis spp. and Toxoplasma gondii impacts aquatic and terrestrial species worldwide, and recent evidence suggests prevalence is increasing in free-ranging marine mammals.^1,3,6 Severity and disease presentation vary but often include encephalitis, polyphasic rhabdomyositis, and/or hepatic disease.^1,4-7,9 Results of a survey disseminated to institutions across North America indicated that serologic testing (IFAT²), though not validated in species other than sea otters, is the most common tool for ante-mortem diagnosis and monitoring in wild and managed marine mammals. However, the association of serologic titer with clinical disease throughout treatment and recovery is poorly understood in these species.

Serologic results from 47 individual marine mammals across 8 species were evaluated for changes over time, either during treatment and/or as clinical signs progressed. Thirty-one animals either had no significant clinical signs or had clinical resolution with treatment; four of these were never treated. Twenty of these 31 animals had persistently elevated titers on most recently obtained recheck. Serum titers from 11 of the 31 individuals decreased to less than or equal to 1:320 (positive cut-off) between two weeks and seven months following initiation of therapy. The remaining 16 of 47 animals either died in treatment or were euthanized due to clinical decline. Of these, only 1 showed a decreased titer. Elevated titers may be indicative of progressive or persistent infection, however, similar to findings in other species (humans¹⁰ and cats²), individuals can also maintain elevated titers for at least several months following clinical resolution of protozoal disease.

Acknowledgements

The authors thank the UC Davis One Health Institute Laboratory for providing the protozoal serology testing utilized in this study, as well as the numerous institutions that provided data on diagnosis and management of protozoal disease in marine mammals through the AAZV listserv.

*Presenting author
+Student presenter

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