The California sea lion population has fallen prey to a devastating bacterial outbreak.
It's the second largest outbreak of leptospirosis on record, with at least 220 reported cases so far in 2018, according to the Sausalito-based Marine Mammal Center, which has been treating infected animals.
The number of sea lions infected with the potentially fatal bacteria represents more than half of all sea lion rescued this year, according to the center.
The overall West Coast sea lion population, which is larger than 250,000 animals and has tripled since the 1970s, is not in any danger. But the uptick in infections this year has left officials scratching their heads.
Over the last several months, the center has treated about five sick sea lions per day, primarily off the northern California coast. The infection causes kidney disease and often, failure.
Infected mammals are typically found stranded on the beach, according to Dr. Shawn Johnson, director of veterinary science at the Marine Mammal Center. He says most of them are spotted curled up on the beach with their flippers tucked in.
"You can tell they don't feel well," Johnson told KQED. "They tend to have very severe abdominal pain, they're very dehydrated, they're very lethargic."
Johnson says outbreaks seem to occur on a 4 to 5-year cycle. The last major event was in 2011, when nearly 200 infected sea lions were treated by the center’s hospital.
The majority of infections occur between July and November, according to the center, which has been tracking the disease for more than four decades.
Animals diagnosed with leptospirosis are treated with antibiotics, fluids and gastroprotectants for any ulcers. About two-thirds of infected animals do not survive.
While scientists are unsure of what is driving the periodic outbreaks, UCLA researchers suspect that a combination of factors may be to blame, including changes in the animal's immunity, sea surface temperatures and migration patterns.
To learn more about the disease, MMC and UCLA researchers will work together to collect blood and urine samples from wild sea lions at Año Nuevo Island in Northern California. The animals are tagged and released once samples have been retrieved.
Researchers will be looking at blood samples to find evidence of kidney disease and antibodies that indicate past exposure to leptospira. The urine samples tell scientists whether the animal is currently infected.
Infected sea lions usually show signs of the disease, including drinking water and folding the flippers over the abdomen, according to the center.
Marine mammals generally do not ingest water because they obtain all the fluid they need from other food sources. But when infected, the animals will drink water to compensate for failing kidneys that are no longer able to effectively filter toxins and regulate hydration.
Other animals, such as humans and dogs, can become infected with leptospira through contact with contaminated soil, urine, or water.
You can protect yourself and pets by keeping a safe distance from marine mammals of at least 50 feet. If you see a sick animal, report it to the center’s 24-hour hotline at 415-289-SEAL (7325).