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DENVER/April 6, 2018 – Morris Animal Foundation-funded researchers have shown that California sea lions with more genetic diversity are less likely to recover from leptospirosis, a deadly bacterial disease.

The researchers, from the Autonomous University of Queretaro in Mexico and the University of California, Davis, found this surprising result after reviewing MHC class II molecules from more than 100 sea lions’ blood and tissue samples. The team published their results in the journal Infection, Genetics and Evolution.

Leptospirosis is found around the world and affects a wide variety of animals, including marine mammals. In sea lions, it can cause dysfunction of the kidneys and liver, which results in dehydration, vomiting, stranding and death. Outbreaks of the disease occur roughly every four to six years among free-ranging sea lions in the Pacific Northwest. Although in many cases the disease is easily identified, the factors that contribute to disease susceptibility often remain unclear.

Researchers analyzed DNA from skin and blood samples from more than 100 sea lions that stranded along California and Oregon coasts from 1995 to 2005 and had received treatment at California’s Marine Mammal Center. Specifically, the team examined the associations between the sea lions’ MHC class II genes’ configuration and diversity, and susceptibility to leptospirosis.

“This was a very unexpected discovery, but an important one as we continue to understand the relationship between genetics and infectious disease severity,” said Karina Acevedo-Whitehouse, an immune ecologist at Mexico’s Autonomous University of Queretaro, and primary investigator of the study.

Acevedo-Whitehouse believes this result is because the more genetically diverse sea lions’ immune systems are triggered in excess as they recognize different parts of the bacteria, leading to a “storming” attack that actually causes many of the symptoms that sea lions with leptospirosis exhibit.

MHC class II molecules, critical components of the immune system, are encoded by a set of genes that are highly polymorphic. The MHC molecules differentiate what is and what is not part of an organism. In theory, if an organism has a more diverse set of these genes, they are better able to recognize different parts of pathogens. In this study however, researchers found sea lions with a higher numbers of different variations of their MHC class II molecules paradoxically were less likely to recover from leptospirosis infections.

“We’re grateful for this team’s work on this project and advancing the science. The more knowledge we have, the more likely it is in the future to come up with a solution or a treatment for leptospirosis outbreak that threaten marine mammals,” said Tiffany Grunert, Morris Animal Foundation’s Acting President and CEO.

About Morris Animal Foundation

Morris Animal Foundation’s mission is to bridge science and resources to advance the health of animals. Founded by a veterinarian in 1948, we fund and conduct critical health studies for the benefit of all animals. Learn more at