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. If not treated, the bacteria can cause irreversible kidney damage.
The Marine Mammal Center is currently responding to the second largest leptospirosis outbreak on record in California sea lions. Read more about the current outbreak. For media inquiries, please email media@tmmc.org.
Leptospirosis is caused by a spiral-shaped bacteria called Leptospira. Veterinarians can usually identify leptospirosis in a patient even before laboratory tests confirm a diagnosis because of the infection’s distinctive symptoms in California 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 hydration they need from food sources. But when they are infected with the Leptospira , their kidneys stop functioning properly and cannot filter toxins or regulate hydration.
Sea lions diagnosed with leptospirosis are treated with antibiotics, fluids and other supportive care, such as gastroprotectants for stomach and intestinal ulcers. Unfortunately, even with treatment, roughly two-thirds of the animals that strand with acute leptospirosis do not survive.
However, research using data and samples collected at The Marine Mammal Center, as well as data collected from sea lions in the wild, indicate that many sea lions infected with Leptospira survive and likely experience mild or no symptoms of the disease, unlike the acute cases seen at our hospital.
Leptospirosis is a major health burden for humans, domestic animals and wildlife worldwide with over 500,000 severe cases in humans every year. Leptospira can cause disease ranging from infection with no symptoms to severe and possibly fatal disease.
The type of Leptospira affecting California sea lions at The Marine Mammal Center is a strain that has also been associated with pigs, skunks and foxes. It’s transmitted via urine, either directly or via contaminated water or soil.
Researchers haven’t definitively determined how transmission occurs within the sea lion population, but they believe it occurs primarily while sea lions are hauled out on land. The bacteria may also survive for short periods in seawater, so transmission may be possible when large groups of sea lions gather in the water.
When a leptospirosis outbreak occurs, our scientists study the disease to learn more about what causes an outbreak and how we can improve treatment for infected animals. Thanks to the Center’s 43 years of stranding records and bank of blood and urine samples, researchers have a unique opportunity to investigate the disease patterns over four decades.
The graph above shows the seasonal nature of these outbreaks, reflected in large numbers of California sea lions stranding and being treated at the Center for clinical signs of kidney failure. © The Marine Mammal Center
For over 10 years, scientists at The Marine Mammal Center have collaborated with researchers at the Lloyd-Smith Laboratory in the Department of Ecology and Evolutionary Biology at UCLA to study the dynamics of this pathogen in the California sea lion population. The Center has been on the forefront of research on leptospirosis in marine mammals and has published a number of scientific papers on the disease dating back to 1985.
Leptospira was first detected in California sea lions in 1970 during a leptospirosis outbreak that occurred along the coast of California, Oregon and Washington. And since the 1980s we have seen yearly, seasonal outbreaks with major outbreak events causing 100 or more sea lion strandings happening every four to five years.
The reasons for these periodic major outbreaks in sea lions is unknown, however our UCLA collaborators believe that a combination of factors may be responsible, such as changes in herd immunity, sea surface temperatures and sea lion migration patterns.
Interestingly, after 30 uninterrupted years of seeing at least a few cases of leptospirosis annually, the disease disappeared from the population in late 2013 only to reappear four years later. Researchers at UCLA believe the disappearance of the disease may be related to the highly anomalous oceanographic conditions that occurred during the same time period. The abnormally warm waters, commonly referred to as “the Blob,” may have caused changes in sea lion behavior and migration patterns as they struggled to find food sources.
Since 2009, the Center’s biologists and veterinary staff have taken blood and urine samples from wild juvenile California sea lions at popular haul-out spots in the San Francisco and Monterey Bay areas. These animals are then tagged and released, and the urine and blood samples help researchers learn more about kidney function and exposure rates among these animals.
This collaborative research project also relies on long-term demographic datasets generated by our partners at the NOAA Fisheries Marine Mammal Laboratory. These biologists monitor and track pups born on the Channel Islands every year. We also work closely with biologists in Oregon and Washington who monitor the sea lions in those areas.
Many different animal species, including humans and dogs, can become infected with Leptospira through contact with contaminated urine, water or soil. The Marine Mammal Center has a number of safety protocols in place to prevent transmission to veterinarians and volunteers working with our sea lion patients.
