Leptospirosis in dogs: symptoms, infection and prevention

Overview

Leptospirosis ranges from infection without signs to life-threatening systemic illness. Acute kidney injury is a common presentation in dogs. Liver disease may develop alongside kidney injury. In a less common severe form, bleeding occurs in the lungs. The disease is therefore more than a passing fever.

Leptospirosis occurs worldwide. It is more common in warm, wet regions. One northern European country recorded 12 canine cases in 2024 based on veterinary notifications. Reported numbers do not include every possible symptom-free infection.

Leptospira bacteria have different surface-based variants called serovars. Their occurrence varies geographically. This also affects vaccine choice.

Causes

Urine from an infected animal is an important means of bacterial spread. Rodents and shrews maintain infection in the wild. They may shed bacteria in urine without appearing ill themselves. Other wildlife and domestic animals can also spread infection.

Bacteria enter through mucous membranes or broken skin. Exposure can occur when drinking contaminated water. Urine-contaminated soil, food or bedding can also transmit infection. Direct contact with a shedding animal's urine is another route.

Warm, damp conditions and stagnant surface water favour bacterial survival. In suitable conditions, bacteria can survive in the environment for weeks to months. Incubation is about 2–14 days. Bacteria spread through the body and can disrupt the blood-vessel lining.

Bacteria can remain in kidney tubules and later be shed in urine. A surface-adhering biofilm helps them persist in kidneys and the environment.

Risk factors

Any age, breed or sex can be affected. Risk is not confined to large males or dogs living mainly outdoors. Infection has also been diagnosed in small urban dogs. Affected puppies as young as 11 weeks have been described.

Wading in stagnant water and contact with rodents increase exposure opportunities. Heavy rainfall and flooding can increase infection risk. The disease occurs in the Baltic countries and north-western Russia, for example. Travel therefore affects risk assessment.

Poorly secured compost or poor hygiene can increase rodents near the home. Outbreaks have also occurred in dog day care and kennels. Cold weather reduces bacterial survival outdoors. Direct animal contact can nevertheless transmit infection even in unfavourable environmental conditions.

Leptospirosis is also suspected when kidney function suddenly worsens in a dog with existing kidney disease. Old dogs can be affected too.

Typical symptoms

Early feverish illness may be vague. You may notice changes such as:

• Fever and a clear decline in general condition.
• Loss of appetite.
• Vomiting or diarrhoea.
• Increased thirst and urination.
• Tiredness, weakness or reluctance to move.
• Muscle tenderness, stiffness or trembling.
• Yellowing of the eyes or gums.

As kidney injury worsens, urine output may instead decrease or stop. Increased drinking can precede a clear rise in kidney blood values. Abdominal pain may occur. Bleeding can appear as tiny spots in skin or mucous membranes. Respiratory signs may indicate lung injury.

Inflammation inside the eye is a less common sign. Low body temperature, swelling, or eye and nasal discharge are also possible.

Complications and consequences

A dog recovering from acute kidney injury may return to previous function. Some are left with chronic kidney disease. Long-term liver damage is also possible. Severe clotting disorders and major organ injury can cause death.

Mortality in leptospiral pulmonary haemorrhage syndrome has reached 70%. This concerns that severe syndrome rather than every infection. Intensive supportive care can nevertheless give severe kidney injury a good outlook. In one study of 36 dogs, more than 80% recovered with dialysis after previous conventional treatment had been insufficient. The result concerns dogs selected for dialysis.

Raised bilirubin and impaired clotting are poor prognostic factors. Kidney tissue repair may continue for weeks to months. Recovery therefore does not always end at hospital discharge.

Acute liver disease can also occur without concurrent kidney injury. Muscle pain may relate to inflammation of blood vessels, muscles or kidneys.

Diagnosis at the vet

The vet asks about onset, possible water and animal exposures, travel and vaccinations. Results are interpreted together with signs, vaccination records and other findings. Blood and urine tests assess organ injury. Kidney values such as urea and creatinine can rise. Liver disease may raise bilirubin and liver enzymes.

Urine may contain protein, blood or inflammatory cells. Glucose may enter urine despite normal blood glucose. The blood count may show reduced platelets. Clotting tests may be needed to investigate bleeding.

PCR looks for bacterial genetic material in blood or urine. Samples are collected before antibiotics where possible. Both blood and urine are preferably tested during acute illness. A negative PCR does not exclude disease. Bacterial urine shedding can be intermittent.

The MAT test measures antibodies against Leptospira. Early results may be negative. At least a 4-fold antibody rise supports recent infection. Paired samples 7–14 days apart are recommended. One sampling protocol uses an interval of 1–3 weeks.

Vaccination or previous symptom-free infection may explain positive antibodies. Positive urine PCR may also involve symptom-free carriage. Chest imaging may reveal changes compatible with haemorrhage.

Urine concentrating ability may decrease. Blood potassium can be too low or high. Increased blood acidity may also be detected. Abdominal imaging may show enlarged kidneys. The liver may be enlarged too. Vaccine-induced antibodies do not themselves make PCR positive.

Treatment

The vet prescribes treatment and medicines. Leptospirosis is treated with antibiotics and support for affected organs. With strong suspicion, treatment is not postponed while awaiting confirmation. Doxycycline is also used to eliminate bacterial carriage in the kidneys. A vomiting dog may initially receive an intravenous penicillin-group medicine.

Hospital care and intravenous fluids are often needed initially. Fluid, electrolyte and acid–base balance are corrected individually. Nausea, pain and nutrition are managed as needed. Blood pressure is monitored and treated. Respiratory failure may require oxygen or mechanical ventilation.

Excessive fluids can worsen organ injury, particularly in a dog with lung signs. Urine production, weight and breathing are therefore monitored closely. Severe kidney injury may need dialysis. Dialysis support is usually not required for more than 1–2 weeks.

In hospital, kidney and liver values and electrolyte balance may be checked every 24 hours. After discharge, re-examination is recommended within 1 week at the latest. Follow-up includes blood and urine tests. With treatment, kidney values often return to reference ranges in about 10–14 days. Some dogs have permanent injury.

Plasma transfusion can replace deficient clotting factors. The blood count may be monitored every 48 hours in hospital. The red blood cell volume fraction may be checked every 24 hours. A urine collection system helps measure output. Once kidney values stabilise and fluid balance is maintained, intravenous fluids are withdrawn gradually.

Prevention

Reduce contact with stagnant water, wetlands and animals spreading bacteria. Rodent control around homes and animal housing lowers risk. Keep an affected dog away from other dogs and dog parks. Routine hygiene also applies when handling animals without signs.

Some veterinary authorities recommend vaccination for dogs travelling to areas where infection is common. International recommendations also support vaccination of all dogs regardless of lifestyle or breed. Individual need is assessed according to local risk and travel plans. Remember other dog vaccinations too.

Vaccines protect for at least 12 months. Protection mainly targets the serogroups included in the vaccine. Vaccination reduces clinical disease and bacterial shedding risks. It does not guarantee complete protection against carriage. Vaccination needs are also assessed after illness because lifelong protection is uncertain.

Serious adverse reactions to leptospiral vaccines have not been more frequent than with other common canine vaccines. Breed and size can affect reaction risk regardless of the vaccine antigen.

In experimental studies, the combined protection of 21 vaccine products against clinical disease exceeded 80%. These involved experimental challenge, so the percentage does not directly describe protection for every pet dog in natural conditions.

Important for dog owners

Tell the practice about suspected exposure, travel destinations and signs in other animals. Bring vaccination records and note drinking, urination, vomiting and onset. Follow discharge monitoring and hygiene instructions. New reduction in urination, breathing difficulty or marked deterioration requires contact with the veterinary team.

Wear protective gloves when cleaning urine and wash hands after handling your dog. Possible splashing also requires eye protection. Appropriate doxycycline treatment rapidly reduces urinary bacterial shedding, within about 48 hours. Nevertheless, continue precautions for the full period instructed by the practice.

Transmission risk from dog to human is low with basic precautions. People can also be exposed through the same environment as the dog. If you become ill or are concerned about urine exposure, contact your own healthcare service and mention the dog's illness. In some countries, vets and laboratories must report suspected leptospirosis to the relevant authority.

Frequently asked questions

Can an indoor dog get leptospirosis?

Yes. Disease is not confined to large outdoor dogs. Infections have also been described in small urban dogs. Assessment considers walking routes, water and rodent contact, and travel; small size does not exclude disease.

Can leptospirosis spread to humans?

Yes. It is a zoonosis, a disease transmissible from animals to humans. An infected animal's urine is an important exposure route. People may also encounter the same urine-contaminated environment as a dog. Wear gloves when cleaning urine and wash hands carefully.

Does a negative test rule out leptospirosis?

Not always. Antibodies may not yet be measurable early in acute disease. A negative PCR does not exclude it either. Bacterial urine shedding may be intermittent. The vet combines tests with the clinical picture and decides on repeat samples.

Can a vaccinated dog become ill?

Yes, although vaccination reduces risk. Infections have occurred even in appropriately vaccinated dogs. Vaccination does not prevent every possible carrier state. A dog with signs is therefore investigated regardless of vaccination, and vaccination history informs antibody interpretation. Vaccination does not itself make PCR positive.

Will my dog recover completely?

Full recovery is possible. However, some dogs are left with chronic kidney or liver disease. Kidney tissue repair can take weeks to months. Severity of organ injury and treatment response affect the outlook. Follow-up after discharge helps identify ongoing care needs.

Do other household dogs need testing?

Dogs in the same home may have shared exposure. The vet assesses testing and possible preventive treatment for other dogs. Do not start the affected dog's medicines or human antibiotics yourself without an individual veterinary decision.