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This week a number of dogs frequenting the same dog park in Fresno, California, are reported to have been infected with leptospirosis, a serious bacterial disease. An increase of cases among pet dogs was also seen in the Denver areaearlier this year.

Leptospirosis can affect humans, dogs, and many other animals. It is caused by several strains, or “serovars,” of bacteria of the Leptospira genus. In the U.S. there are eight different serovars of Leptospira that can infect dogs.

Not all animals that are exposed to Leptospira become sick with the disease, and cases can be mild. Sometimes, however, the effects can be severe. Although treatable with antibiotics, acute onset of the disease can damage organs such as the kidneys and liver and be life threatening. Initial symptoms in dogs can vary widely but often include lethargy, vomiting, and diarrhea. Unfortunately, these symptoms can mimic those of other illnesses.

Humans who contract leptospirosis can also become very sick. A serious outbreak among humans is occurring this summer in Mumbai, India, with 54 cases reported so far just this month, and a fatality rate of nearly one-third—the unusually high mortality rate due to many of those cases going untreated. Most of the cases in Mumbai have been in the wake of heavy flooding in the area in mid-June. Humans exposed to infected floodwater can pick up the disease through a skin wound.

The disease-causing bacteria can be found in water that has been contaminated by the urine of infected animals including raccoons, skunks, opossums, rats, deer, and other wildlife as well as pets or livestock. The bacteria require moisture to live but can survive in water, mud, or damp soil for months, especially in warmer climates.

Dogs can become infected by direct or indirect contact with the urine of an infected animal, or by wading, drinking, or swimming in stagnant water or floodwater that has been contaminated. This can include ponds, puddles, or muddy dog parks. In some recent cases, vets believe that dogs have picked up the disease in their own backyards, where infected wildlife have presumably passed through.

When a pet or livestock animal is sick with leptospirosis, humans can become infected through contact with the animal’s urine or body fluids.

Increase in Cases

In Oregon, veterinarians have observed a steady re-emergence of the disease in dogs since 2009. In 2010, leptospirosis was found to be the cause of hundreds of dead and dying sea lions along the Oregon coast.

Canine leptospirosis: Growing in effect and threat”, by Pedro Pauliz, DVM, PhD, of the Western University of Health Sciences in Pomona, California, notes the incidence of infected dogs on the rise in the U.S. One study of 33,000 samples showed a 600-percent increase in dogs testing positive for the bacterium between 2000 and 2007. The report also notes that raccoons have been identified as major reservoirs of the pathogen in the U.S., and that up to 90 percent of urban rats shed the bacteria in their urine, indicating that dogs in urban, suburban, and rural environments may be equally at risk of exposure.

According to the American Animal Hospital Association, leptospirosis is common in areas of the U.S. where temperatures are mild and where there are notable rainy seasons. However, the number of cases in more arid parts of the country, such as Colorado, has increased in the last few years.


The Centers for Disease Control and Prevention provides information on leptospirosis and guidelines for preventing occurrence of the disease in pets.

The leptospirosis vaccine is not included with the regular “core vaccines” given routinely to dogs by many animal hospitals and instead may be recommended where geographic region or the dog’s lifestyle is felt to put them at risk. In the past the leptospirosis vaccine was associated with causing adverse reactions more frequently than other vaccinations. New vaccines, however, may be less likely to cause adverse reactions, according to some vets.

The CDC says that the vaccine does not provide 100-percent protection, noting, “This is because there are many strains (types) of leptospirosis (the bacteria that causes leptospirosis), and the vaccine does not provide immunity against all strains.”

Guidelines for protecting pet dogs:

Discuss with your veterinarian whether the vaccination for leptospirosis is right for your dog, weighing possible risks and benefits.
Keep rodent populations under control.
Avoid leaving pet food outside your home that could attract raccoons, rats, and other wildlife.
Try to limit your dog’s exposure to stagnant or standing water, especially if leptospirosis cases have been reported in dogs in your area.
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