Infest and infect.

While the world is still reeling from the hantavirus cruise outbreak — and the disease is gaining ground in the US — an entirely different rat-borne disease has claimed the life of one Berkley, California resident.

In a public health release issued this week, the city confirmed that a man had died in May after contracting leptospirosis, a bacterial disease spread through infected urine, particularly rat urine.

According to reports, a second victim who lived with the deceased was also infected but recovered following an extended hospitalization.

The two Berkeley victims were the first confirmed human cases of leptospirosis in the city in more than a decade.

The pair lived together in an RV about a mile from Harrison Street, a homeless encampment in North Berkeley that has been at the center of an ongoing leptospirosis outbreak among rats and dogs since late 2025.

City Manager Paul Buddenhagen said the two occupants were using the RV to trap, feed and breed wild rats. The victim’s vehicle was so thick with vermin that 200 rats allegedly had to be removed before the RV was ultimately destroyed.

Dr. Peter Chin-Hong, an infectious disease expert at UC San Francisco, said the sheer number of rodents dramatically increased the risk of infection.

“The more rats you have, the more urine you might have, and you increase the chance of at least one of the rats having an infection,” he told SFGATE. “It’s like playing rat roulette.”

The two people “fell sick, but they did not seek medical care for weeks and possibly months,” Buddenhagen wrote in a memo to the City Council. That delay “is thought to have contributed to the severity of their disease.”

Leptospirosis, caused by the bacterium Leptospira, can persist for months in soil and water. In addition to rat urine, it’s also found in the urine of pigs, cattle, horses, dogs, and other wild animals.

Infected animals may not show any symptoms that they’re carrying the bacteria, according to the CDC.

People get infected when they come into contact with the bacteria through touching contaminated soil or water. The bacteria enter through the eyes, ears, mouth, or a cut or scratch in the skin. Leptospirosis is rarely spread person-to-person — so cases typically remain isolated. 

However, the bacteria thrive in places lacking basic services like indoor plumbing, running water, or refrigerated food storage, making encampments prime breeding grounds for an outbreak.

In light of these two recent human cases, Berkeley Public Health’s response strategy is shifting to “citywide sanitation and targeted hygiene outreach for individuals experiencing unsheltered homelessness, vehicle residency, or who are otherwise living in heavily rodent-infested environments.”

The agency is also urging medical providers to consider leptospirosis when treating patients who have been exposed to rats and develop compatible symptoms. 

Folks are also urged to protect their pets. Vaccines are available for dogs, and the risk of exposure can also be reduced by avoiding muddy puddles and stray rats.

What are the symptoms of leptospirosis?

Leptospirosis is usually asymptomatic in humans. However, early signs and symptoms are often flu-like, including a high fever, headache, chills, muscle aches, diarrhea and rash.

It can last anywhere from a few days to several weeks, according to the CDC.

If medical attention is sought promptly, leptospirosis can be treated with antibiotics. If left untreated, leptospirosis can cause kidney failure, meningitis, liver damage, or death.

Despite last month’s fatality, Chin-Hong stressed that the disease is usually treatable when caught early: “Nobody should die of lepto. It is a bacteria. It is treatable by antibiotics that every hospital has.”

How to prevent leptospirosis

While the city of Berkeley maintains that the risk of contracting leptospirosis from rats remains very low for the vast majority of residents and business owners, there are many ways you can reduce your risk of exposure.

Wearing protective clothing, washing your hands regularly, and covering any open cuts or wounds significantly mitigates the risk of infection.

For those living in or near encampments or other high-risk areas, experts also recommend consuming clear, clean drinking water, washing fruits and vegetables harvested from these areas, keeping food and water in closed containers, minimizing trash and other items that could attract rats and create rat nests, and avoiding exposure to rats and their body fluids.

In 2024, amid a spike in leptospirosis cases in New York City, the city recommended the following precautions.

Always wear shoes when you take out the trash (and take them off when you get inside), and you can also wear gloves (which you remove immediately upon coming back into your house).

If you can’t avoid areas where rats have been or could be, clean surfaces and floors with a diluted bleach solution (1 part bleach, 10 parts water) to kill bacteria.