Every four to five years, The Marine Mammal Center sees a surge in the number of California sea lions that are admitted with symptoms of leptospirosis, a bacterial infection that affects the kidneys and can be lethal for patients. If not treated, the bacteria can cause irreversible kidney damage.
Recent outbreaks of leptospirosis have occurred in 2011 and in 2008. In 2008 nearly 200 sea lion patients were admitted with the condition, an increase over the previous year. When numbers are high, our scientists can take advantage to study the disease with the hope of finding out why outbreaks occur and how we can help those animals infected.
Leptospirosis is caused by spiral shaped bacteria called Leptospira. Veterinarians and volunteers can usually identify leptospirosis in a patient even before laboratory tests confirm the diagnosis because of the infection's distinctive symptoms in sea lions, which include drinking water and folding the flippers over the abdomen. Marine mammals generally do not need to drink water because they receive all the moisture they need from food sources; but when they are infected with the Leptospira bacteria, their kidneys, which filter toxins, stop functioning properly. The animals thus cannot regulate their hydration and need to drink water to compensate for that loss. Infected sea lions have even been spotted sucking sand in an attempt to extract water. If the disease is caught early enough and treated with antibiotics, patients may recover. However, leptospirosis is often fatal, as once the kidneys are damaged beyond repair, the animal will go into renal failure and die. Despite veterinarians' best efforts, approximately two thirds of the Center's leptospirosis patients die.
Many different animal species, including humans and dogs, can become infected with Leptospira bacteria through contact with contaminated urine, water, or soil. In California sea lions, epidemics of the bacterial infection were first documented in the early 1970s. The reasons for repeated epidemics in sea lions are unknown, as it is still unclear whether the organism in sea lions is one only affecting these animals, or whether it could come from domestic species or terrestrial wildlife reservoirs. Recent studies suggest a combination of factors may be responsible, and more research is necessary to determine the causes of cyclical outbreaks in the population.
To further that research, The Marine Mammal Center has spearheaded a leptospirosis study in collaboration with the National Oceanic Atmospheric Administration, University of California Los Angeles, the Center for Diseases Control, University of California Davis, Penn State University, and the National Animal Disease Center in Ames, Iowa. In October 2009, the Center's biologists and veterinary staff began taking blood samples, tagging, and releasing wild juvenile California sea lions at popular haul-out spots for the animals in the San Francisco and Monterey Bay areas.
"The blood samples the Center's team collected from wild California sea lions will help them determine kidney function and exposure rates among these animals," says Dr. Jeffrey Boehm, Executive Director at The Marine Mammal Center. "The data also will help us to understand more about the susceptibility of sea lions in the population during an epidemic and clarify the relationship between the stranded sea lions with leptospirosis we see here at the Center, and those that are susceptible in the population."