Leptospirosis Outbreaks in California: What Dog Owners Need to Know
A bacterial disease known as leptospirosis has been reported in dogs across multiple regions of California, with outbreaks documented in Los Angeles County and the Bay Area. The disease, which can cause severe illness in dogs and, in rare cases, transmit to humans, has been linked to factors including dog daycare environments, low vaccination rates, and contaminated standing water.
Los Angeles County 2021 Outbreak
A 2021 outbreak of leptospirosis infected over 200 dogs in Los Angeles County, according to research led by the University of California, Davis. The study, published in the Journal of Clinical Microbiology, traced the outbreak to dog daycare environments where close contact may have accelerated dog-to-dog transmission. The infections were caused by Leptospira interrogans serovar Canicola, a strain covered by the canine leptospirosis vaccine.
Low vaccination rates in the Los Angeles area, attributed to the arid climate where the bacteria were previously considered low risk, contributed to the outbreak.
The study analyzed 59 confirmed cases and over 15,000 control patients. As vaccination rates increased and some daycare facilities temporarily closed, the outbreak subsided.
Bay Area and Regional Spread
Health departments across California, including in the Bay Area and Los Angeles, have issued warnings regarding a spike in leptospirosis cases in dogs. Veterinarians in the Bay Area, including Dr. Katherine Geating of the San Francisco SPCA and Dr. Kim Carlson of Lenity Vet Specialists + Emergency Care in San Mateo, have reported a significant increase in cases.
The city of Berkeley issued a public health alert after an outbreak at a homeless encampment. Researchers are investigating cases in homeless encampments in Berkeley and Oakland, where dogs, wildlife, and environmental conditions may create transmission pathways. Early findings show high infection rates in local rat populations.
Disease Characteristics and Transmission
Leptospirosis is a bacterial infection that can damage the kidneys and liver in both dogs and humans. The bacteria can be transmitted through contact with contaminated water, soil, mud, or urine from infected animals, primarily rats. The bacteria can remain viable in standing water for 30 days or longer.
- Transmission spikes during rainy periods.
- Standing water in areas such as dog parks can create environments with high concentrations of the bacteria.
- Dogs can contract the disease by licking their paws after walking through contaminated water.
- Small children may also be at risk if they touch infected animal paws and then their mouths.
Symptoms
Symptoms in dogs include increased thirst, increased urination, decreased appetite, lethargy, vomiting, and reluctance to move. Symptoms in humans typically include flu-like symptoms.
Human Cases and Tracking
Leptospirosis is a zoonotic disease, meaning it can transfer from animals to humans. No human cases were linked to the 2021 Los Angeles County outbreak. Human cases in California are considered rare, but some counties have reported them. San Francisco reported one human case in the current year. San Mateo County reported two cases in 2018 and 2024. Experts state the disease may be underdiagnosed in people.
Tracking of animal leptospirosis cases is not uniformly required by state or local health departments in California, though some jurisdictions, such as Santa Clara and Los Angeles counties, do track them.
Past Outbreak Statistics
The 2021 Los Angeles County outbreak resulted in hundreds of cases, 13 dog deaths, and 91 hospitalizations.
Prevention and Treatment
Early diagnosis and treatment are essential for affected animals. Treatment for positive cases requires isolation, appropriate antibiotics, and, in some cases, urinary catheterization to prevent further spread within veterinary facilities.
The leptospirosis vaccine is recommended as a protective measure for dogs and requires an annual booster for full effectiveness. Untreated pets can shed bacteria for weeks to months, while appropriate treatment can stop shedding within a few days to a week.
Vaccination is the most effective way to protect dogs and reduce transmission risk to people.
Veterinarians and researchers state that leptospirosis is expected to become more common as climate change brings more flooding.
Owners who suspect their pet has been exposed or shows symptoms should seek veterinary care immediately.