Leptospirosis in Dogs: What You Need to Know - Whole Dog Journal (2023)

Leptospirosis is a disease caused by bacteria that is excreted in the urine of infected animals. Deer, skunks, and raccoons are the major reservoirs, although rodents such as mice and rats also carry it. Leptospirosis typically causes severe kidney and liver damage, which can sometimes be fatal. It is a zoonotic disease, meaning it also infects humans.

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


The leptospire is a special type of bacteria called a spirochete. It is unique from other bacteria because it cannot be easily cultured in a laboratory, making it challenging for your vet to definitively diagnose your sick dog.

Leptospira 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 become ill; they simply carry the organism with them and expel it in their urine. The leptospires do not reproduce once they enter the environment, but they can survive for weeks or even months in warm, wet conditions. He likes standing water, puddles and muddy ground – this is where you and your dog will encounter him the most.

Species that become ill with leptospirosis are called accidental hosts. These include both dogs and humans. The leptospire enters the occasional host through mucous membranes (either while swimming or drinking from mud puddles) or through breaks in the skin (again, either from swimming or simply digging through mud with cuts or open wounds).

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


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

Leptospirosis is a worldwide disease, most common in areas with high rainfall and warmer climates. In the United States, Hawaii is the main hotbed for leptospirosis, but cases have been documented across the country. Numbers are high on the West Coast, in the upper Midwest, as well as in the Northeast, Southeast, and Mid-Atlantic coastal areas. The number of cases in the United States peaks in the late fall.

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

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 an increase in cases of leptospirosis in urban areas has been documented, it is hard for me to believe that the amount of urine a mouse leaves is equivalent to that of a deer in terms of exposure. However, no risk is better than low risk, which is why rodent control is recommended in urban environments.


Leptospirosis in Dogs: What You Need to Know - Whole Dog Journal (1)

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

Less common but possible symptoms include muscle pain, abdominal pain, and inflammatory eye disease. If the lungs are damaged, breathing difficulties and coughing up blood can occur. Fortunately, lung disease, which has a much worse prognosis, is not common.

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

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

The best way to know for sure is to look at paired samples, one taken immediately (the acute titer) and one taken two weeks later (the convalescent titer). If this shows a 4-fold or greater titer increase, it is considered diagnostic of leptospirosis. But we can't wait two weeks to start treating leptospirosis! It is imperative that your dog is started on the correct antibiotic treatment as soon as possible.

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

Here are two more factors that can confound the diagnosis: Vaccinated dogs can still succumb to an active infection! And dogs vaccinated against leptospirosis will show vaccine-induced antibodies on a titer test!

This means that when a vaccinated dog comes in with signs suggestive of leptospirosis and has a positive titer for MAT, there is no way to distinguish active infection antibodies from vaccine-induced antibodies. Does he have leptospirosis or not? Time will tell. In the meantime, you can bet I'll be spoiling him with it.

A polymerase chain reaction (PCR) test is currently available that looks for the actual DNA of the leptospire organism and is unaffected by vaccination status. These tests can identify diseases earlier, but their accuracy is still under investigation. This means that if the PCR is negative, it is still sensible to start treatment if the vet's index of suspicion is high.


Although diagnosis can be difficult, treatment is easier. The Leptospire organism is not sensitive to many antibiotics, but fortunately it ismuchsensitive to a few. This means that if your dog receives a quick, accurate diagnosis and proper treatment is started early in the course of the disease, you can usually expect a good outcome; as many as 80% of dogs treated this way will make a full recovery.

Appropriate antibiotic treatment is paramount for a successful outcome. Penicillin, or its derivative ampicillin, is usually initiated early as these drugs remove the bacteria from the bloodstream. Doxycycline is usually given for at least two weeks, as this antibiotic helps clear the organism from the kidneys. If necessary, antiemetics (anti-vomiting agents) and painkillers are given.

Treatment almost always involves hospitalization for several days or longer, depending on the severity of the disease. Renal and hepatic involvement requires aggressive intravenous fluid therapy and close professional monitoring. Patients with severe renal failure unresponsive to intravenous fluid therapy should be referred to a specialized dialysis center.

Once your dog is discharged from hospital, he will need to be closely monitored for several months, although a good prognosis can be given at this point.

Your vet will advise you on how to handle your dog's urine safely at home, including wearing gloves when cleaning up. Routine household disinfectants that contain bleach are effective against this bacteria, so it would be wise to use a garden sprayer and bleach solution to spray any area of ​​your yard where your dog urinates.

If you have other dogs, ask your vet to proactively treat the others with doxycycline, just to be safe. I know my dogs drink from the same puddles and run through them when we are out. If one is infected, chances are the other has been exposed.


Effective control of rodents, both indoors and outdoors, is always a good idea. A fenced yard helps prevent the larger wildlife reservoirs, such as deer, from urinating where your dog goes outside. Besides keeping your dog in a bubble, there is always an environmental risk of your dog being exposed to leptospira!

This is where vaccination comes into play. The canine leptospirosis vaccines 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—over 200 different leptospirosis serovars have been identified—they are the most common. In addition, the vaccine provides some cross-protection against the other serovars. In fact, there is some evidence that vaccinated dogs that become infected with leptospirosis may experience less severe disease.

I recommend waiting until 12 weeks of age to start the leptospirosis vaccine. The first series requires two doses three weeks apart. After that, a booster is given annually. In places where vets see high cases, your vet may recommend boosting more frequently, perhaps every six to nine months, based on their clinical experience.


You may have heard or had your own negative experiences with the leptospirosis vaccine in the past. As a practicing veterinarian, I can confirm that years ago this vaccine appeared to cause significantly more and significantly worse side effects in dogs than other vaccines. The smaller breeds, especially Pugs and Dachshunds, were clearly overrepresented when it came to reactions related to the leptospirosis vaccine. Small breed breeders often warn their puppy buyers about the danger of this vaccine and strongly discourage it.

Fortunately, this is no longer the case with the vastly improved vaccines used today. Recent studies have shown that this vaccine is no more reactive than any other routine dog vaccine.

However, vaccination is never without risk, so I recommend a disease risk assessment for each individual dog before deciding which vaccines are appropriate for that particular dog. Every time you or your dog gets a vaccine, you accept a certain risk. Reactions range from mild (only malaise 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 an autoimmune disease.

This is why if your dog is at minimal or no risk of contracting a disease, it may not make sense to expose your dog to the risks associated with vaccination. Current vaccination guidelines from the American Animal Hospital Association support this idea by listing leptospirosis as a "non-core" vaccine, meaning it may not be suitable for all dogs. Examples of core vaccines recommended for all dogs include distemper, parvovirus and rabies.

The bottom line is that you should not be afraid of getting a leptospirosis vaccine for your dog, but do a thoughtful risk assessment, taking into account your environment and lifestyle, before making a decision. If your yard is accessible to skunks, raccoons and deer, or if you have one a large population of wild animals close to your home puts your dog at greater risk. Dogs that camp or hike in areas where wildlife is present are also at higher risk.

In the end, it is up to you whether you want to vaccinate your dog against leptospirosis or not. As always, the best advice for you and your dog comes from your vet.

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