What Is Leptospirosis?
Leptospirosis is a bacterial infection caused by spiral-shaped bacteria called Leptospira. It is one of the most widespread zoonotic diseases in the world, meaning it can spread between animals and humans, which makes it significant not only for dog health but for public health. In dogs, it can cause severe kidney and liver failure, and without prompt treatment, it is frequently fatal.
There are hundreds of Leptospira serovars — essentially different strains — though only a handful commonly infect dogs. The most significant serovars in the UK and Europe include Leptospira icterohaemorrhagiae, Leptospira canicola, Leptospira grippotyphosa, and Leptospira bratislava. Modern lepto vaccines are designed to cover the serovars most relevant to a given region.
How Dogs Are Exposed
Water is the primary route of exposure, which is why leptospirosis is sometimes called rat fever or swamp fever. The bacteria are shed in the urine of infected animals — most commonly rats, but also cattle, foxes, hedgehogs, and other wildlife. When infected urine contaminates water sources or wet soil, the bacteria can survive for weeks to months under mild, damp conditions.
Dogs become infected by:
- Swimming in or drinking from ponds, rivers, puddles, or flooded ground
- Wading through wet mud or waterlogged grass
- Contact with infected animal urine through skin wounds or mucous membranes
- Ingesting infected soil, water, or contaminated food
Dogs that swim regularly, live in rural or semi-rural areas, or have frequent access to standing water are at highest risk. However, urban dogs are far from immune — rats are ubiquitous in cities, and contaminated puddles or drainage areas pose a real risk. Lepto cases have been documented in dogs that never left urban environments.
Symptoms to Watch For
Leptospirosis can present in several ways depending on which organs bear the brunt of the infection and how quickly treatment begins. The incubation period is typically between five and fourteen days. Initial symptoms are often non-specific and can be mistaken for many other conditions:
- Sudden fever and shivering
- Severe lethargy and reluctance to move
- Vomiting and diarrhoea, sometimes with blood
- Loss of appetite
- Muscle pain and stiffness
- Increased thirst and urination, followed by reduced urination as kidneys fail
As the disease progresses, signs of organ failure become apparent. Jaundice — yellowing of the skin, gums, and whites of the eyes — indicates liver involvement. Dogs with significant kidney damage may produce very little urine despite drinking heavily, and may develop fluid retention. Bleeding abnormalities can cause blood in urine, bruising on the skin, or bleeding from the gums.
The speed of progression varies. Some dogs deteriorate within 24 to 48 hours of first symptoms. This is not a disease to observe at home for several days before seeking veterinary advice.
Diagnosis and Treatment
Diagnosing leptospirosis requires blood and urine testing. Key findings typically include elevated kidney and liver enzyme values, low platelet counts, and sometimes jaundice on physical examination. Specific serology tests detect antibodies against Leptospira, though early in the infection antibody levels may not yet be detectable. PCR testing of blood or urine can identify the bacteria directly and is increasingly available in veterinary diagnostic laboratories.
Treatment requires hospitalisation. The core components are:
- Intravenous fluids to support kidneys and correct dehydration
- Antibiotics — penicillin or doxycycline are the agents of choice
- Management of kidney failure, which may include specialised dialysis in severe cases
- Monitoring and management of liver function
- Careful handling by veterinary staff due to zoonotic risk
Dogs with leptospirosis that receive early and aggressive treatment can survive, but the prognosis worsens significantly once kidney or liver failure is established. Some surviving dogs develop chronic kidney disease as a lasting consequence of the infection.
The Zoonotic Risk to Humans
Leptospirosis in humans, sometimes called Weil's disease in its severe form, can cause acute liver and kidney failure and is potentially fatal. Humans are exposed through contact with infected animal urine — including from their own dogs — particularly via cuts, mucous membranes, or the eyes.
If your dog is diagnosed with or suspected of having leptospirosis, strict hygiene is essential. Wear gloves when handling the dog, their urine, or any contaminated surfaces. Wash hands thoroughly after contact. Inform your GP if you develop flu-like symptoms in the weeks following exposure. This is not a reason to panic, but it is a reason to take sensible precautions.
Vaccine Protection: What to Know
The leptospirosis vaccine is included in the routine vaccination schedule in the UK and is considered a core vaccine by most UK veterinary guidelines. The L4 vaccine, which covers four serovars, is widely used and recommended over the older two-serovar formulations, particularly for dogs with outdoor or water-related exposure.
Unlike the distemper or parvo vaccines, lepto vaccine immunity does not last as long. Annual boosters are necessary to maintain protection, and if a booster is missed by more than a few months, a full primary course of two injections may need to be repeated. Puppies receive two initial doses, three to four weeks apart, with annual boosters thereafter.
Vaccination does not provide absolute protection against all Leptospira serovars, but it significantly reduces the risk of infection from the most common ones and reduces the severity of illness if infection does occur. For dogs that swim regularly or live in high-risk areas, keeping the lepto vaccine strictly up to date is one of the most important preventive measures available.