What’s Killing Sea Otters? Scientists Pinpoint Parasite Strain

by Kristin P Burns
August 22, 2019

Genetic Link Found Between Deadly Pathogen and Wild and Feral Cats on Land

Many wild southern sea otters in California are infected with the parasite Toxoplasma gondii, yet the infection is fatal for only a fraction of sea otters, which has long puzzled the scientific community. A study from the University of California, Davis, identifies the parasite’s specific strains that are killing southern sea otters, tracing them back to a bobcat and feral domestic cats from nearby watersheds.

The study, published this week in the journal Proceedings of the Royal Society B, marks the first time a genetic link has been clearly established between the Toxoplasma strains in felid hosts and parasites causing fatal disease in marine wildlife.

The study builds on years of work by a consortium of researchers led by the UC Davis School of Veterinary Medicine’s Karen C. Drayer Wildlife Health Center and the California Department of Fish and Wildlife (CDFW). The scientists were called upon in the late 1990s to help decipher the mystery when Toxoplasma caused deaths in sea otters along the California coast.

“This is decades in the making,” said corresponding author Karen Shapiro, an associate professor with the UC Davis School of Veterinary Medicine and its One Health Institute. “We now have a significant link between specific types of the parasite and the outcome for fatal toxoplasmosis in sea otters. We are actually able to link deaths in sea otters with wild and feral cats on land.”