Abstract

The observation that only some Toxoplasma gondii infected southern sea otters (Enhydra lutris nereis) succumb to fatal toxoplasmosis has long puzzled wildlife veterinarians and professionals. This investigation combined molecular characterization and pathological examination data of T. gondii in sea otters, providing a unique opportunity to evaluate whether parasite strain influences pathological outcomes. Molecular findings were further combined with data on T. gondii genotypes circulating in sympatric terrestrial carnivores to examine spatial associations among parasite strains on land and sea. Genotyping was performed on 135 T. gondii isolates obtained from sea otter brains, with 116 of these animals also receiving comprehensive pathological examination. The predominant T. gondii genotypes identified were Types X, atypical mixed II/X, and X variants. These atypical strains accounted for 79% of T. gondii isolates with the remainder belonging to Type II. Type X or mixed X variants were the only strains isolated from brains of otters that died due to T. gondii as a primary cause of death. Spatial analysis revealed identical T. gondii genotypes circulating in terrestrial carnivores and sea otters in central California. Notably, of four sea otters that had atypical, mixed Type II and X alleles in Monterey Bay, two shared 100% sequence identity across three loci with a T. gondii strain obtained from a feral cat in the same region.¹ Results demonstrate a land-sea connection of virulent T. gondii strains and highlight how fecal contamination of coastal waters can deliver lethal pathogens to the nearshore, with detrimental impacts on marine wildlife.

Acknowledgments

The authors would like to thank staff at the California Department of Fish and Wildlife, especially Francesca Batac and Laird Henkel for their assistance with project logistics. We also thank volunteers and staff at CDFW, The Monterey Bay Aquarium, The Marine Mammal Center, and other stranding agencies for their efforts to recover sick and dead-stranded sea otters along the central California Coast. Brittany Dalley, Lezlie Rueda, and Mitchell Ng, are acknowledged for technical assistance with molecular characterization assays. Financial support for this work was provided by the AAZV Wild Animal Health Fund.

^aAuthors contributed equally

Literature Cited

1.  VanWormer E, Miller MA, Conrad PA, Grigg ME, Rejmanek D, Carpenter TE, Mazet JAK. Using molecular epidemiology to track Toxoplasma gondii from terrestrial carnivores to marine hosts: implications for public health and conservation. PLoS Negl Trop Dis. 2014;8: e2852.