Leptospirosis in Dogs

What is leptospirosis?

Leptospirosis is the disease that results from infection with Leptospira bacteria (a group of spiral-shaped bacteria called spirochetes), which is found in soil and water and spread through the urine of an infected animal. The bacteria can remain viable in the environment for weeks to months, depending on conditions. It is especially prevalent in areas with high rainfall and warm climates. All dogs are at risk of infection, regardless of breed, age, geographic location, lifestyle, and time of year. 

Infection occurs through exposure of mucous membranes (mouth nose, eyes) or skin wounds to urine or urine-contaminated water, soil, food or bedding. It can also be spread through contact with an infected carcass or tissues from an infected animal, through breeding, or being bitten by an infected animal, although these routes of transmission are rare compared to environmental exposure. Pregnant dogs can pass the bacteria to their puppies. Once it enters the host, the bacteria move into the bloodstream and quickly spread throughout the body.

Dogs that are exposed to slow or non-moving water sources, including ponds and lakes, rivers, and streams, as well as those that may be exposed to wildlife or farm animals that could be infected, are at increased risk of infection. Dogs that frequent dog parks or boarding facilities and dogs that kill rodents or reptiles are also at risk.

Although infected dogs may infect humans and other animals, cases of transmission from infected dogs are rare.

What are the clinical signs of leptospirosis in dogs?

Clinical signs of leptospirosis vary in dogs and are largely dependent on the strain of bacteria involved, as well as the dog’s individual immune response. Infected dogs may show no clinical signs, exhibit mild illness that they recover from on their own, or develop a severe, life-threatening condition. Infected dogs that seem healthy can still spread the bacteria in their urine.

Since the disease spreads throughout the body in the bloodstream, it can affect multiple systems and organs. Common clinical signs of leptospirosis include loss of appetite, vomiting, abdominal pain, diarrhea, increased thirst and urination, and weight loss. Affected dogs may be lethargic, exhibit jaundice, fever, and have muscle pain and stiffness. The bacteria commonly target the kidneys and liver, which is why many affected dogs show signs related to these organs. Severe cases can lead to liver and/or kidney failure, severe lung disease and difficulty breathing, heart damage, and bleeding disorders.

Contact your veterinarian promptly if your dog shows sudden lethargy, vomiting, decreased appetite, increased thirst or urination, jaundice, or difficulty breathing, especially if there has been possible exposure to standing water or wildlife and your dog is not vaccinated for leptospirosis.

How is leptospirosis diagnosed in dogs?

Leptospirosis in dogs is diagnosed through evaluation of exposure history, vaccination status and clinical signs. However, the clinical signs of leptospirosis overlap with many other diseases. Physical examinations, blood tests, urine tests, x-rays, and ultrasound examinations may be used to aid in diagnosis. Specialized blood tests and PCR testing are often needed to confirm infection.

How is leptospirosis treated in dogs?

Leptospirosis in dogs is treated with antibiotics. Early antibiotic treatment not only helps the dog recover but also reduces bacterial shedding in the urine, lowering the risk of transmission. Additional medications, fluid therapy, oxygen therapy, breathing support, dialysis, and nutritional support may be required depending on the severity of the disease and the clinical signs.

What is the prognosis for leptospirosis in dogs?

The prognosis for dogs affected by leptospirosis is good when treated early; however, permanent kidney damage is possible. Dogs that survive severe infection may require long-term monitoring of kidney or liver function. The prognosis is generally poor for dogs that exhibit severe respiratory or kidney disease.

How can leptospirosis be prevented in dogs?

All dogs should be vaccinated for leptospirosis. Initially, two vaccinations, four weeks apart, are recommended, followed by annual boosters. Modern leptospirosis vaccines are safe, and serious adverse reactions are uncommon. Since outbreaks of leptospirosis have occurred in boarding and daycare facilities, proof of vaccination should be required for these facilities. Current vaccines protect against the most common disease-causing strains.

Additional preventative measures include reducing dogs’ exposure to sources of Leptospira bacteria. Avoid letting dogs swim in or drink from slow-moving or stagnant water such as marshy areas, ponds, rivers, and lakes. Since farm animals and wild rodents are also sources of infection, limit exposure to these animals, including carcasses, through appropriate rodent control and fencing.

Although transmission from dogs to humans is rare, it is recommended to always wash your hands after handling pets, avoid contact with pets’ urine and quickly clean up and disinfect urine in the home, and avoid allowing dogs to urinate in areas where other dogs may drink or play in standing water.

For more information

What we still don’t know about leptospirosis in dogs, DVM360, February 2026

An Update on the Diagnosis and Management of Leptospirosis, Today’s Veterinary Practice, February 2025

Leptospirosis in dogs, American Veterinary Medical Association

Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. J Vet Intern Med. 2023; 37(6): 1966-1982.

Sykes, J. E., Gamage, C. D., Haake, D. A., & Nally, J. E. Understanding leptospirosis: application of state-of-the-art molecular typing tools with a One Health lens. American Journal of Veterinary Research 2022; 83(10).