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leptospirosis in dogs comes from contaminated water

Leptospirosis in dogs. Symptoms, treatment and prevention

Leptospirosis is a potentially fatal bacterial infection, mostly spread through the infected urine of rats and other rodents, but can also be found in contaminated water, like puddles, canals, farmlands and stables. It is more common during the wetter months of the year. The bacteria get into your dog's body through cuts, scratches or the thin linings of the nose, mouth and eyes and can cause liver and kidney damage or failure. In this article, we will discuss leptospirosis symptoms, prevention and treatment, as well as answer the most important questions surrounding this nasty infection.  

Brief summary 

  • Leptospirosis is a potentially fatal infection spread by rat urine and can be found in contaminated water. 

  • Symptoms of leptospirosis in dogs include fever, lethargy, vomiting and diarrhoea. 

  • Leptospirosis can be treated with antibiotics to kill the bacteria and your vet will also treat the symptoms.  

  • There is a core vaccine for leptospirosis which will be adminstered as part of your dog’s routine vaccination schedule.

What is leptospirosis? 

Leptospirosis is a disease caused by bacteria (Leptospira). This bacteria is mainly spread through the urine of infected animals, such as rats, other rodents, infected dogs and occasionally other animals, such as pigs or cows. It is usually found in warm, wet environments and standing water like puddles, canals, floodplains, rivers and farmland. The bacteria is quite hardy and can survive in the environment for a long time, especially in stagnant water and wet soil.  

Leptospirosis is also a 'zoonotic' disease, which means it can be passed to people. Humans also contract leptospirosis through contact with infected urine. It is known as Weil's disease in people.

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Symptoms of leptospirosis in dogs

If your dog is infected with leptospirosis, you might not realise for a while because it usually takes 8-10 days (sometimes as long as two weeks) for the symptoms to start showing. It is even more difficult because the early signs are often vague and can be confused with other illnesses, such as brucellosis in dogs.  

Early symptoms of leptospirosis include 

  • Fever 

  • Lethargy (sleeping more, not wanting to go for walks or play) 

  • Loss of appetite 

  • Muscle pain, limping 

  • Inflamed eyes 

  • Vomiting

  • Diarrhoea 

  • Bleeding from the mouth or eyes 

As well as this, your dog may seem depressed. Of course, this looks different from dog to dog, but as a pet owner, you'll be perfectly placed to understand if your dog isn't their usual self. 

After the initial infection, the bacteria will travel through the bloodstream toward the liver and kidneys. This can lead to organ damage which can lead to symptoms such as: 

mouth ulcers as a symptom of leptospirosis

What causes leptospirosis in dogs? 

Leptospirosis is caused by bacteria. The most common way for leptospirosis to spread in dogs is through water contaminated with urine from infected rats.  

The bacteria that cause the infection live in warm, stagnant water, usually found in rivers, canals, ponds, farmland and wetlands. Leptospirosis can spread easily if it's been raining heavily for a while. Dogs become infected when their mucous membranes (such as inside the mouth or nose) or a wound or cut to the skin come in contact with the infected urine, including urine-contaminated water, soil, bedding or food. Rarely, it can pass from mother to pups via the placenta. 

Although the main carrier of leptospirosis is rats, it can spread through other mammals, including squirrels, livestock (pigs and cattle) and dogs. One of the reasons it is so contagious is that many dogs that have the disease and recover can still be carriers, which means although they aren't ill or showing any symptoms, they are 'carrying' the bacteria and sending it out into the world every time they pee. 

Because of this, dogs can also pick up the infection when they come into contact with bedding, toys or food bowls that have been in contact with infected urine.  

When should I see my vet? 

If your dog starts showing any of the above symptoms, especially if they have been around water recently, then contact your vet immediately. Early detection is key to combating this illness, so don't wait until your dog is ill before getting help. 

leptospirosis dog visiting vet

Leptospirosis diagnosis  

Quickly diagnosing and treating leptospirosis in dogs is vital for a happy outcome. Your vet may use a few tests when diagnosing leptospirosis in your dog. These are a complete blood count (CBC), biochemical profile, urinalysis and specific tests for the bacteria.  

Complete blood count

Infected dogs will show some changes to their red and white blood cells such as anaemia, increases to some white blood cells and decreased platelets.  

Biochemical profile

The biochemical profile is a series of blood tests that help vets see how well your dog's major organs are working, including the liver and kidneys. Because leptospirosis attacks the liver and kidneys, these blood tests will show if they're damaged.  


Urinalysis is a urine test that concentrates on the kidneys. It will look at the concentration of urine, proteins and sugars that shouldn't be there and can show signs of inflammation.  

Other tests that can be used are DNA-PCR and Microscopic Agglutination Tests (MAT) to look for more specific evidence of infection with leptospirosis.  

DNA-PCR test

This test is similar to the tests we've become used to during the Covid pandemic. They look for the DNA strands of the bacteria and can be run on either blood or urine. The issue with the PCR test is they can sometimes give false negatives, where your dog will be carrying the infection, but the test thinks it isn't. 

MAT test

The MAT test looks for antibodies in your dog's blood against leptospirosis. If they're found and are rising, infection is likely.  

Leptospirosis treatment  

Your vet will prescribe your dog antibiotics, most likely ones called doxycycline. These antibiotics work by killing the bacteria or stopping them from spreading. They give your dog's natural immune system time and help fight the infection whilst also helping your dog feel better. It is essential your dog completes the course of antibiotics to help them recover and kill the loitering bacteria that can cause your dog to become a carrier. This will help them stay healthy and reduce the risk to dogs they meet.  

Antibiotics will work better if the infection is caught early. For severe cases, long-term treatment might be needed. If your dog's kidneys are injured, or they end up with liver disease, they may need supplements, specialised diets or fluids to help them stay healthy. Unfortunately, organ damage caused by severe infection may be irreversible. 

Severe cases of leptospirosis will require hospital treatment and have no guarantees of success because of the excessive damage to the internal organs. If your dog shows any symptoms, contact your vet immediately. 

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Leptospirosis prevention 

Thankfully there is a vaccine for leptospirosis. It is usually included as part of your dog's routine vaccination schedule. The vaccination is given in two vet visits, the second three to four weeks after the first. Following this, a booster is offered annually to keep your dog fully protected. Keep puppies away from potential areas of infection until they are fully covered - this includes unvaccinated dogs, farms and freshwater sources. 

It is a sensible precaution to keep your dog out of standing or stagnant water where possible, especially during the wetter months. If possible, stop your dog from drinking from puddles. You'll have to carry a small collapsible water bowl and water bottle to ensure they have a fresh supply. Pest control is crucial if you live in a rural area or near water where rodents might be. Preventing rodent infestations will reduce the risk to your dog.

Common leptospirosis questions 

Is the leptospirosis vaccine safe? 

Whilst there have been some reports in the media about the increased dangers and side effects of the L4 (leptospirosis) vaccine, the statistics don't show this to be true. Indeed, the number of dogs who react badly to the L4 vaccine is less than seven in 10,000, but 10-15% of dogs diagnosed with leptospirosis won't recover. 

It must be remembered that side effects are possible with all vaccines, whether canine or human, and there are some common side effects you should be ready for. These are mild and only last 24-48 hours. They include mild lethargy, a slight fever or a reduced appetite.  

lethargic dog caused by leptospirosis vaccination

Is leptospirosis common in dogs in the UK? 

Leptospirosis is still relatively uncommon in the UK. The dogs most at risk are working farm dogs and those living in rural areas or places where the rodent population is particularly high, especially if unvaccinated. 

What dogs are at high risk for leptospirosis? 

Your dog will be at higher risk from leptospirosis if they live on a farm, kill rodents, or spend a lot of time swimming or drinking from standing water. Unvaccinated dogs are at much higher risk than those fully vaccinated. 

Can leptospirosis be passed to humans? 

Yes, humans can be infected with leptospirosis from dogs, but it is rare. You would have to come in contact with their urine, blood or bodily fluids. Those most at risk are vets, dog breeders and farmers. If your dog has tested positive for leptospirosis, observe optimal hygiene, such as wearing gloves when disposing of soiled bedding or cleaning contaminated surfaces.  

Need more advice?

Urine samples are a great way of diagnosing health issues, and collecting them in a space where your dog feels comfortable will help keep them calm and happy.
If you have any questions, it's always best to contact your vet because they can tailor their advice to your dog, their breed and your situation.

Find your nearest vet using our Find a Vet page, or speak to a vet online using Online Vets.

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