Leptospirosis is a bacterial infection dogs catch from standing water, wildlife urine, and contaminated soil. It primarily attacks the kidneys and liver and can be fatal within a week if untreated. It's also zoonotic — infected dogs can pass it to people. Vaccination is now considered a core recommendation for at-risk dogs.
Last reviewed: May 2026
How Dogs Catch Leptospirosis
Leptospira bacteria are shed in the urine of infected animals — rats, raccoons, skunks, opossums, deer, and other dogs. The bacteria survive for weeks in warm, moist soil and standing water. Dogs are infected when contaminated water or urine enters through mucous membranes (eyes, nose, mouth) or breaks in the skin. Drinking from puddles, ponds, ditches, or stagnant water is the most common exposure route.
Cases peak in late summer and fall, especially after heavy rain or flooding. Urban dogs are increasingly affected — rats in cities are a major reservoir, as outlined by the FDA Animal Health Literacy, 2024.
Early Signs Owners Notice First
The incubation period is 4 to 12 days. Early signs are vague and flu-like: fever (often 103 to 105°F), lethargy, loss of appetite, vomiting, increased thirst and urination, and muscle soreness that can look like reluctance to climb stairs. About 50 percent of dogs develop a mild yellow tint to the gums or whites of the eyes within the first week.
These signs are easily mistaken for a stomach bug. Any combination of fever, vomiting, and unusual thirst in a dog that has been near standing water or wildlife in the past 2 weeks deserves leptospirosis testing.
Advanced Signs — Kidney and Liver Failure
As the bacteria multiply in the kidneys, dogs develop acute kidney injury: dramatically increased then suddenly decreased urination, dehydration, brown-tinted urine, and rising blood urea levels. Liver damage causes jaundice, vomiting bile, and clotting abnormalities — about 20 to 30 percent of affected dogs develop bleeding signs such as bloody stools, nosebleeds, or bruising. A subset of dogs develops leptospiral pulmonary hemorrhage syndrome, which carries a 70 percent mortality rate.
How Vets Diagnose Leptospirosis
Diagnosis combines clinical signs with lab testing. The standard tests are PCR on urine and blood (highest sensitivity in the first week) and the microscopic agglutination test (MAT), which measures antibody titers — a 4-fold rise between two samples taken 2 weeks apart confirms recent infection. Bloodwork typically shows elevated kidney values (BUN, creatinine, SDMA), low platelets, and liver enzyme elevation. Urinalysis often shows protein loss and glucose despite normal blood sugar.
Treatment is started on suspicion — not after diagnosis — because delays worsen outcomes.
Treatment — Antibiotics and Aggressive Supportive Care
The first-line antibiotic is doxycycline for 14 to 28 days, which both kills the bacteria and clears the carrier state. IV ampicillin or penicillin is used initially in dogs too sick to keep down oral medication. Supportive care includes IV fluids to support failing kidneys, anti-nausea medication, blood pressure monitoring, and in severe cases hemodialysis — which has dramatically improved survival in dogs with anuric kidney failure.
With early treatment, survival is around 80 percent. Dogs presenting in advanced kidney failure or with pulmonary hemorrhage drop to 30 to 50 percent. Many survivors have lasting kidney damage that requires ongoing management.
Prevention — Vaccination Is the Key Step
The current 4-serovar Leptospira vaccine protects against the four most common US serogroups (Canicola, Icterohaemorrhagiae, Pomona, Grippotyphosa). The AAHA Canine Vaccination Guidelines, 2022 now list leptospirosis as a core vaccine in most US regions because of how widespread exposure has become.
Initial series: two doses, 3 to 4 weeks apart, starting as early as 12 weeks of age. Annual boosters thereafter. Adverse reactions are uncommon but small-breed dogs have slightly elevated risk of acute hypersensitivity — premedicating with diphenhydramine is sometimes recommended.
Other preventive steps include preventing dogs from drinking standing water, keeping outdoor water bowls covered, controlling rodent populations on the property, and avoiding swimming in stagnant ponds or slow-moving streams during late summer and fall, as advised in the AAHA Canine Life Stage Guidelines, 2019.
When to See a Vet
Early lepto looks like a generic illness. The exposure history is what tips the scale toward urgent evaluation.
Call your vet today if:
- Fever, lethargy, and decreased appetite for more than 24 hours
- Increased thirst and urination starting suddenly
- Recent drinking from puddles, ponds, or flood water
- Recent wildlife or rodent exposure
- Vaccine more than 12 months out of date
Go to the ER immediately if:
- Vomiting with severe lethargy or weakness
- Yellow gums or eyes (jaundice)
- Bloody urine, bloody vomit, or black tarry stool
- Sudden inability to urinate or noticeably less urine output
- Difficulty breathing or coughing up blood
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Frequently Asked Questions
Can people catch leptospirosis from a dog?
Yes. Leptospirosis is zoonotic — humans can be infected through contact with the urine of an infected dog or contaminated surfaces. Wear gloves when handling urine, towels, or cages, clean contaminated surfaces with diluted bleach (1:10), and wash hands thoroughly. Doxycycline post-exposure prophylaxis may be recommended for exposed family members. Pregnant women and immunocompromised people should avoid direct contact entirely.
How much does leptospirosis treatment cost?
Outpatient treatment with oral doxycycline runs $300 to $800 including diagnostics. Hospitalized dogs requiring IV fluids and monitoring typically cost $2,000 to $5,000 over 4 to 7 days. Severe cases requiring hemodialysis can exceed $8,000 to $15,000. Vaccination is far cheaper at $20 to $50 per dose, with annual boosters thereafter.
Is the leptospirosis vaccine safe for small dogs?
Yes, with low overall risk. Small-breed dogs have a slightly higher rate of acute hypersensitivity reactions (~1 in 500 doses) compared with large breeds. Premedication with diphenhydramine and observation for 30 minutes post-vaccination further reduces risk. The vaccine is recommended for at-risk small dogs because the disease is more dangerous than the rare reaction.
How long is a dog contagious after infection?
Untreated infected dogs shed Leptospira in urine for months to years. With appropriate doxycycline treatment, shedding usually stops within 1 to 2 weeks. Continue to handle urine with gloves until your vet confirms a negative urine PCR if anyone in the household is immunocompromised.
Can a vaccinated dog still get leptospirosis?
Yes — but cases in vaccinated dogs are usually milder. The vaccine covers the most common serogroups but doesn't cross-protect perfectly against every Leptospira strain. Vaccinated dogs that contract a covered serogroup typically develop limited illness and recover with treatment.
Still Not Sure if Your Dog Needs a Vet?
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