California Dog Warning Issued After Deadly Bacteria Found

California residents and pet owners in the San Francisco Bay Area have been warned about an outbreak of a potentially dangerous disease.

Why It Matters

Berkeley, California, is facing a significant public health challenge after the detection of leptospirosis—a potentially fatal bacterial disease transmitted by rats—in a homeless encampment. 

The alert, issued by local health authorities, underscores heightened risks for dogs and residents, especially following a period of heavy rainfall that has created favorable conditions for bacteria to thrive. 

What To Know

Berkeley officials issued a public health alert after discovering leptospirosis among multiple rats and at least two dogs living near the Harrison Street encampment, located by Codornices Creek. 

Leptospirosis is caused by leptospira bacteria, which are typically spread through the urine of infected animals—most commonly rats—contaminating soil and stagnant water.

While no human cases have been reported as yet, the disease poses significant dangers to both animals and people, particularly those exposed to contaminated water or soil. 

Dogs are particularly at risk because they tend not to avoid puddles of water in the same way humans do, according to Dr. Monica Gandhi, an infectious disease physician at UCSF, who also explained that the bacteria do not spread between people, so the illness poses a greater threat to animals than to humans.

“Dogs don’t avoid puddles the way people do,” she told SFGATE. “They’re much more likely to be exposed.”

People and animals become infected primarily when contaminated water or soil comes into contact with cuts, eyes, the mouth, or mucous membranes. 

According to the city, the combination of warm weather followed by recent storms has created optimal conditions for the bacteria’s survival and transmission. The bacteria can persist in soil or water for up to a month, increasing the risk of more infections long after the initial contamination.

Officials designated the Harrison Street area as a ‘red zone’ and strongly urged encampment residents to move at least one-third of a mile away to enable focused cleanup, rat eradication, and public safety measures. 

The city has posted warnings, conducted environmental testing, and called on pet owners to vaccinate their animals against leptospirosis. 

Owners of free-roaming cats are also encouraged to consider vaccination, while all pet owners should prevent animals from drinking potentially contaminated water.

Symptoms and When to Seek Care

Anyone who has spent time in the encampment area and develops flu‑like symptoms—including fever, chills, headache, sore muscles, or red eyes—should seek medical care immediately and mention possible leptospirosis exposure. 

Dog owners should watch for vomiting, jaundice, or abnormal urination and seek urgent veterinary care.

What People Are Saying

Dr. Peter Chin-Hong, infectious disease expert at UC San Francisco, told SFGATE: “Wherever you get rats urinating and then flooding or rain, there’s potential for exposure. The combination of warmth followed by rain is kind of a bad setup for leptospirosis.”

Dr. Gandhi said: “There’s no human-to-human transmission. Each individual has to be exposed to infected animal urine or contaminated soil or water.”

She added: “The incubation period can be long. People may not remember that exposure, which is why clinicians need to ask about contact with animals, rodents or contaminated environments.”

Berkeley’s public health officer, Dr. Noemi Doohan, said in a public health release: “Neither dogs nor people should wade in, or drink from, nearby water, mud, puddles, or Codornices Creek. Provide clean water for your pets, and keep them away from sick or dead animals.”

What Happens Next

Berkeley authorities have launched an ongoing public health investigation and expect cleanup and rat eradication activities to take at least 30 days—the typical lifespan of leptospirosis in soil.

“Additionally, eradication of rats requires many cycles of baiting the rats with poison in their underground burrows, removing the carcasses and rebaiting over a period of time,” the city explained.