Leptospirosis: The Disease, Not the Vaccine
Leptospirosis can damage a dog's kidneys and liver, and it can spread to people. The signs, who is at risk, and how to protect your household during treatment.
Written by thecanineledger
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If your dog is lethargic, off food, vomiting, drinking or peeing much more or much less than usual, or has yellow gums or eyes: see a vet today. If your dog is struggling to breathe or coughing up blood: go now. Tell the clinic if your dog swims, drinks from puddles or ponds, or has contact with rats.
The 2023 consensus statement on leptospirosis, written for the American College of Veterinary Internal Medicine, warns that the disease is not only a risk for farm dogs. It “continues to be prevalent in dogs, including in small breed dogs from urban areas, puppies as young as 11 weeks of age, geriatric dogs, dogs in rural areas, and dogs that have been inadequately vaccinated” (Sykes et al., Journal of Veterinary Internal Medicine 2023).
While most writing on leptospirosis is about the vaccine, the disease itself is what owners need to recognise. It can damage the kidneys, the liver and the lungs, and it can spread to people. This page covers the signs, the risks, and how to keep your household safe while your dog is treated.
1. What it is, and how dogs catch it
Leptospirosis is caused by Leptospira bacteria. The Merck Veterinary Manual’s owner page says “The disease can affect almost all mammals, including people” (Merck, Leptospirosis in Dogs).
Rats are the main source. The consensus says “the most important reservoir hosts are rodents, especially Rattus norvegicus”, the brown rat.
Water and soil. Infected animals pass the bacteria in their urine. The consensus says the organisms “contaminate soil and water and can remain viable in the environment for weeks to months when conditions are optimal.” Merck adds that “infection is often spread through contaminated water.”
Other routes. Merck lists “contact with contaminated urine or water”, bite wounds or damaged skin, and “eating infected meat or the bodies of infected animals”.
Not only in the country. Because it also spreads by direct contact with rodents, the consensus says “disease can occur in urban regions, and at times of year when organisms survive poorly in the environment.”
2. The signs
Merck: “Some leptospirosis infections cause no signs, while others lead to sudden and severe disease.”
Common signs. The consensus says “Affected dogs may show inappetence, lethargy, vomiting, increased thirst and urination because of non‐oliguric renal dysfunction, fever, or some combination of these signs.” Inappetence means going off food.
Changes in urination. Merck: “Changes in urination are common, ranging from increased urine production to very little or no urine.” A dog that stops peeing is an emergency.
The liver. Merck says the disease “can also cause sudden liver failure, sometimes along with kidney disease, often leading to yellowing of the gums, skin, and eyes.”
The lungs. Some dogs develop bleeding into the lungs. The consensus says this has been “associated with mortality of up to 70%”, “although mild forms exist that can resolve with antimicrobial treatment.”
Our note: A dog that stops peeing is an emergency.
→ Vomiting and Diarrhoea: When It Can Wait and When It Can’t · → Emergency Signs in Dogs: When to Go Now, Not Tomorrow
3. Diagnosis and treatment
Diagnosis takes more than one test. The consensus recommends that “both blood and urine should be submitted”, and warns that “A negative result on blood or urine should not rule out leptospirosis.”
Treatment starts on suspicion. Because of “the marked morbidity and potential mortality of the disease, and the risk of zoonotic transmission”, the consensus says dogs with suspected leptospirosis “should be treated with appropriate antimicrobials”. Zoonotic means it can pass to people. Your vet won’t wait for every result before starting treatment.
Supportive care. Many dogs need hospital care for kidney failure, with fluids and close monitoring.
Recovery. The consensus says kidney values typically return to normal “within 10 to 14 days”. But “Dogs recovering from severe forms of AKI often show various degrees of permanent loss of kidney function”. AKI is acute kidney injury. Your vet should recheck your dog within a week of discharge.
→ Chronic Kidney Disease: What the IRIS Stage Means
Our note: We’ve written “Many dogs need hospital care” without a figure. The consensus doesn’t give one in the sections we read.
4. Protecting your household
The risk from a treated dog is low. The consensus says “Treated dogs returned to the home environment also represent a low risk to household members.” It also notes that the bacteria usually don’t appear in urine until 7 to 10 days after infection.
But take care with urine. The consensus says that “until 48 hours of treatment” has been completed, “owners should avoid contact with their dog’s urine and wear gloves and eye protection when cleaning up urine.”
Merck’s owner page goes further: “Gloves should be worn when cleaning urine, and hands should be washed thoroughly after handling the dog, at least until antibiotic treatment is finished.” Follow whichever your vet advises, and if in doubt, the longer one.
Pregnancy. In the clinic, the consensus says “pregnant humans should avoid contact with these patients.”
Your own health. The consensus says vets should “recommend they contact their medical practitioner if they have questions about the disease in humans.” It also warns that owners “also may be at risk” from the same rodents, wildlife or farm animals that infected the dog.
Our note: The consensus and Merck’s owner page differ on how long to wear gloves. Follow your vet’s advice, or the longer of the two. If someone in your home is pregnant, ask a doctor.
5. Prevention
Vaccination. The consensus recommends that vaccines “should be administered annually to all dogs starting at 12 weeks of age, regardless of breed”. Merck notes that the vaccines “don’t protect against all strains.” Recommendations differ between guidelines and regions. See our vaccine page.
Reducing exposure. The consensus lists “decreased access to potential sources of infection, such as marshy areas and standing water, and minimizing contact with wildlife and domestic animal reservoir hosts using fencing and rodent control.”
Boarding and daycare. The consensus says vaccination “should be required for dogs by boarding or daycare facilities, because outbreaks have occurred in association with such facilities.”
Our note: Guidelines differ on whether every dog needs this vaccine. Our vaccine page covers both views.
→ Core and Non-Core Vaccines: What the 2024 WSAVA Guidelines Say
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “Only farm dogs get leptospirosis” | No. The consensus names small-breed urban dogs, young puppies and older dogs. |
| “A negative test rules it out” | No. The consensus says a negative blood or urine result should not rule it out. |
| “My dog can give it to the whole family” | The risk from a treated dog is low. Avoid contact with urine and wear gloves while cleaning it up. |
| “The vaccine covers every strain” | No. Merck says the vaccines don’t protect against all strains. |
| “Dogs that recover are back to normal” | Not always. Some dogs are left with permanent loss of kidney function. |
Sources
- Sykes JE, Francey T, Schuller S, et al. Updated ACVIM consensus statement on leptospirosis in dogs. J Vet Intern Med 2023: expert consensus; includes CDC authors
- Merck Veterinary Manual: Leptospirosis in Dogs (pet owner version; Roman, DVM, MPH; full review Jun 2026)
Always confirm with your vet before acting on anything on this page.