Leptospirosis in Dogs: What You Should Know


Leptospirosis is a disease caused by bacteria shed in the urine of infected wildlife. Deer, skunks, and raccoons are the biggest reservoirs, although rodents like mice and rats carry it too. Leptospirosis typically causes severe kidney and liver damage, which can sometimes be fatal. It is a zoonotic disease, which means it infects humans as well. 

For all of these reasons, it’s important for dog owners to be aware of this disease, understand how it is spread, know what signs to watch for, and most importantly, learn the best ways to prevent it.


The leptospire is a particular type of bacteria called a spirochete. It’s unique from other bacteria in that it cannot be easily cultured in a laboratory, which makes it a challenge for your veterinarian to definitively diagnose your sick dog. 

The leptospire multiplies in the kidneys of reservoir hosts, such as deer, skunks, and raccoons. Reservoir hosts are those that have adapted to this organism and therefore do not fall ill with disease; they merely carry the organism and shed it in their urine. The leptospire doesn’t multiply once it’s shed into the environment, but it can survive for weeks or even months in warm, wet conditions. It loves stagnant water, puddles, and muddy soil – this is where you and your dog ar most likely to encounter it. 

Species who become ill with leptospirosis are called incidental hosts. These include both dogs and humans. The leptospire enters the incidental host through mucous membranes (either when swimming or drinking from mud puddles) or through breaks in the skin (again, either through swimming or just tracking through mud with cuts or open sores).

Once inside a susceptible host, leptospires multiply rapidly in the bloodstream, where they immediately start damaging the lining of blood vessels. This blood vessel injury then leads to organ damage. The kidneys and liver are most commonly affected, but leptospirosis can cause injury to the lungs, eyes, and central nervous system.


The risk to your dog depends on your geographical location, home environment, lifestyle, and time of year. 

Leptospirosis is a global disease, most prevalent in areas with high rainfall and warmer climates. In the United States, Hawaii is the biggest hot bed for leptospirosis, but cases have been documented all over the country. Numbers are high on the West Coast, in the upper Midwest, as well as in the Northeast, Southeast, and mid-Atlantic coastal regions. Case numbers in the United States peak in late fall.

Home environments with a high neighborhood wildlife population pose a greater risk, especially if your yard is not fenced to keep larger animals like deer out. 

If your lifestyle includes hiking, camping, or walking in parks or wooded areas with your dog, your risk of exposure to leptospirosis is higher. If you live in an urban area with a more sedentary or indoor lifestyle, your risk is much lower, although mice and rats can be carriers. 

While a rise in leptospirosis cases in urban areas has been documented, I’m hard pressed to believe that the amount of urine a mouse leaves behind is as significant as that of a deer in terms of exposure. No risk, however, is better than low risk, so rodent control in urban environments is recommended.


He’s no search-and-rescue dog (he’s not even looking or smelling in the right directions!), but this photo indicates he’s clearly at risk of exposure to leptospirosis, given the proximity of raccoons and their ability to enter his yard. The raccoon is in a tree now, but it was in his yard just minutes before the picture was taken.

If your dog becomes infected with leptospirosis, the signs can be variable but almost always include lethargy and loss of appetite. Fever, vomiting, diarrhea, excessive thirst, and urination are common. Icterus (yellow mucous membranes) frequently occurs when there is liver involvement. 

Less common but possible signs include muscle pain, abdominal pain, and inflammatory eye conditions. If the lungs become damaged, difficulty breathing and coughing up blood can occur. Lung involvement, which carries a much graver prognosis, is fortunately not common. 

Diagnosing leptospirosis in dogs is challenging. Your veterinarian will use a combination of history, physical exam findings, blood tests, and urinalysis to arrive at an initial index of suspicion for this disease. If it’s high enough, the next step includes submission of blood for a test called a microscopic agglutination test (MAT). This test looks for antibodies against leptospirosis. Sounds simple, right? It’s not! 

Several complicating factors make a single MAT insufficient for definitive diagnosis of leptospirosis. First, antibodies are not always identifiable early in the course of a disease. It takes time for the immune system to form antibodies. 

The best way to know for sure is to look at paired samples, one taken right away (the acute titer) and one taken two weeks later (the convalescent titer). If this shows a fourfold or greater increase in titer, it is considered diagnostic for leptospirosis. But we can’t wait two weeks to start treatment for leptospirosis! It’s imperative that your dog be started on appropriate antibiotic therapy as early as possible.

To make matters worse, antibiotic therapy may dampen the rise in the antibody titer we use for making a definitive diagnosis. So while it may well be leptospirosis, it might not look like it, based on a lack of rising titer in the paired samples. This is frustrating, but I have learned that as long as the initial index of suspicion is high enough, the patient receives early appropriate therapy, and makes a full recovery, it’s all good. We just won’t be able to say it was definitely leptospirosis in this situation; we can only say it probably was. 

Here are two more factors that can confound diagnosis: Vaccinated dogs can still succumb to active infection! And dogs who have been vaccinated for leptospirosis will display vaccine-induced antibodies on a titer test! 

This means when a vaccinated dog comes in with signs suggestive of leptospirosis, and has a positive titer on the MAT, there’s no way to differentiate active infection antibodies from vaccine-induced antibodies. Does he have leptospirosis or not? Only time will tell. In the meantime, you can bet I’m treating him for it.

A polymerase chain reaction (PCR) test, which looks for the actual DNA of the leptospire organism and is not affected by vaccination status, is currently available. These tests can identify disease earlier, but their accuracy is still under investigation. This means that if the PCR comes back negative, it would still be prudent to initiate treatment if the veterinarian’s index of suspicion is high.


While diagnosis can be tricky, treatment is more straightforward. The leptospire organism is not sensitive to many antibiotics, but fortunately it is highly sensitive to a few. This means if your dog gets a swift, accurate diagnosis, and appropriate treatment is started early in the course of the disease, you can usually expect a good outcome; as many as 80% of dogs handled in this manner will make a full recovery.

Appropriate antibiotic therapy is paramount to a successful outcome. Penicillin, or its derivative ampicillin, is usually instituted early, as these drugs eliminate the bacteria from the bloodstream. Doxycycline is typically given for at least two weeks, as this antibiotic helps clear the organism from the kidneys. Anti-emetics (anti-vomiting) and pain medications are administered as needed. 

Treatment almost always involves admission to the hospital for several days or longer, depending on the severity of disease. Kidney and liver involvement requires aggressive intravenous fluid therapy and close professional monitoring. Patients with severe kidney failure who fail to respond to intravenous fluid therapy should be referred to a specialty center for dialysis.

Once discharged from the hospital, your dog will require close monitoring for several months, although a good prognosis can be given at this point. 

Your veterinarian will advise you on how to safely handle your dog’s urine at home, which includes wearing gloves when cleaning it up. Routine household disinfectants with bleach are effective against this bacteria, so using a yard sprayer and a bleach solution to spray each place where your dog urinates in your yard would be prudent. 

If you have other dogs, be sure to ask your vet about proactively treating the others with doxycycline, just in case. I know my dogs drink from, and track through, all the same puddles when we are out and about. If one becomes infected, there’s a good chance the other has been exposed. 


Effective rodent control, indoors and out, is always a good idea. A fenced yard will help keep the larger wildlife reservoirs like deer from urinating where your dog goes out. Other than keeping your dog in a bubble, there is always an environmental risk of exposing your dog to leptospires!

This is where vaccination comes in. The canine leptospirosis vaccines that are currently available all protect against four serovars of the bacteria. While the four serovars in the vaccine are not the only serovars your dog may encounter in the United States – more than 200 different leptospirosis serovars have been identified – they are the most common. Furthermore, the vaccine provides some cross-protection from the other serovars. Even better, there is some evidence that vaccinated dogs who become infected with leptospirosis may experience less severe disease.

 I recommend waiting until 12 weeks of age to start the leptospirosis vaccine. The initial series requires two doses, given three weeks apart. Thereafter, an annual booster is given. In locations where veterinarians see a lot of cases, your vet may recommend boostering more frequently than that, perhaps as often as every six to nine months, based on their clinical experience.  


You may have heard about or had your own negative experiences with the leptospirosis vaccine in the past. As a practicing veterinarian, I can attest to the fact that years ago, this vaccine seemed to cause significantly more, and significantly worse, adverse reactions in dogs than other vaccines. The smaller breeds, especially Pugs and Dachshunds, were definitely over-represented when it came to reactions associated with the leptospirosis vaccine. Breeders of small breed dogs would frequently warn their puppy buyers of the danger of this vaccine and strongly advise against it. 

Fortunately, with the markedly improved vaccines in use today, this is no longer the case. Recent studies have shown this vaccine to be no more reactive than any of the other routine canine vaccines.

Vaccination, however, is never without risk, which is why I recommend a disease risk-assessment for each individual dog before deciding which vaccines are appropriate for that dog. Any time you or your dog receives a vaccine, you are accepting a certain amount of risk. Reactions range from mild (just not feeling well for 24 hours) to moderate (hives and/or vomiting and diarrhea) to severe (life-threatening anaphylactic shock). Vaccination can also have delayed reactions that show up weeks later in the form of auto-immune disease. 

That’s why, if your dog has minimal or no risk of getting a disease, it might not make sense to expose your dog to the inherent risks associated with vaccination. The current American Animal Hospital Association Vaccination Guidelines support this idea by listing leptospirosis as a “non-core” vaccine, meaning it may not be appropriate for all dogs. Examples of core vaccines, which are recommended for all dogs, include distemper, parvovirus, and rabies.

The bottom line is, don’t be afraid of getting a leptospirosis vaccine for your dog, but do a thoughtful risk assessment, considering your environment and lifestyle, before deciding. If your yard can be accessed by skunks, raccoons, and deer, or you have a  heavy wildlife population near your home, your dog’s risk is higher. Dogs who are taken camping or hiking in areas where wildlife is present are also at a higher risk. 

Ultimately, whether or not to vaccinate your dog for leptospirosis is up to you. As always, the best advice for you and your dog comes from your veterinarian. 

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