Leptospira bacteria showcasing its distinctive spiral morphology and complex surface structure.
California dog owners are hearing more about leptospirosis, a bacterial disease that has veterinarians sounding the alarm. In the San Francisco Bay Area, a surge of leptospirosis cases followed this winter’s heavy rains, prompting worried owners to call vets about the “lepto vaccine.” Down south in Los Angeles, an outbreak a few years ago left vets baffled as multiple dogs fell ill, some from popular dog daycare and park locations. Leptospirosis (or “lepto” for short) isn’t new — but it is newly on the rise in urban areas, and experts say every dog owner should understand the risks and how to protect their pup.
What is leptospirosis and why the concern?
Leptospirosis is an infection caused by Leptospira bacteria found in water and soil contaminated by the urine of infected animals. Dogs typically contract it by drinking or wading in stagnant water — like puddles, ponds or muddy dog parks — where wildlife such as rats, raccoons, skunks or deer have left bacteria. Historically, lepto was seen more in rural or swampy areas. Now, veterinarians report it in city dogs, too. All dogs are at risk, no matter where they live or how “indoor” their lifestyle.
The disease can attack a dog’s kidneys and liver, leading to serious illness or organ failure. Early symptoms can be vague: lethargy, fever, loss of appetite, vomiting, or excessive thirst and urination are common signs. Because these mimic other illnesses, leptospirosis may go unrecognized until it’s advanced. Prompt antibiotic treatment can cure it if caught early, but untreated cases risk deadly complications. Alarmingly, lepto is zoonotic, meaning it can spread to humans through contact with an infected pet’s urine — so preventing it in dogs also protects pet owners.
Why are cases rising now?
Several factors have contributed to the recent spike in leptospirosis cases in California. One big reason is environmental change — notably, periods of heavy rainfall. Increased rain can create more puddles and muddy areas where leptospira bacteria thrive. UC Davis veterinary professor Jane Sykes says rainfall allows the bacteria to build up as a biofilm on wet soil and surfaces. This helps it persist for weeks to months in the environment. In Northern California, the exceptionally rainy winters have led to more standing water and more opportunities for dogs to encounter the bacteria…