What is Leptospirosis?

File this under ‘Yet Another Thing for Pet Parents to Worry About’: leptospirosis is a zoonotic bacterial disease, meaning it affects both humans and animals, and can readily spread from one species to another (ie, from our dogs to us). Historically, ‘lepto’ cases were most common among farmers and soldiers in tropical climates, however outbreaks in New York City in 2017, and Los Angeles, Corfu and the Pacific Islands in 2023 have claimed the lives of people and their pets, renewing concern over this disease.

Leptospirosis, sometimes referred to as Weil’s disease in humans, is still very unlikely to be spread from pets to humans and is relatively rare in the UK. However, with frequent storms and adverse weather conditions in recent months causing heavy rain and flooding across the UK, the risk of spreading any waterborne disease in contaminated soil or water is increased.

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If your dog contracts leptospirosis, the extent of care needed depends on the severity of disease, and how developed it is at the point of diagnosis, but treatment generally requires a course of antibiotics and supportive therapy. Here’s what you need to know.

What causes leptospirosis?

Leptospirosis in dogs is caused by the Leptospira bacteria, which is spread through the urine of infected animals into the soil and water – most commonly rodents such as rats and mice, and farm animals such as cows and pigs. As dogs come in contact with a contaminated area, the bacteria can be absorbed through their skin (if it is damaged or compromised) and mucous membranes (gums, nose, eyes) or through drinking the contaminated water.

Leptospira bacteria can survive and thrive for weeks to months given the right conditions; namely, warm, damp environments and stagnant water. That said, Leptospira do need moist soils to survive, and they will rapidly die on dry surfaces. Spending time in areas densely populated with other animals (and their urine) increases the risk of exposure.

Symptoms of leptospirosis

The clinical signs of leptospirosis in dogs can be vague and mimic those of many other diseases: fever, lethargy, loss of appetite, muscle stiffness, vomiting and diarrhoea. Jaundice – the yellowish discolouration of the gums or whites of the eyes – can be seen in advanced cases. In more severe cases, this disease moves rapidly and can turn fatal pretty quickly. In mild cases, dogs may show no symptoms at all, and the disease may even go undetected.

How is leptospirosis diagnosed?

Unfortunately, since leptospirosis in dogs often looks like other diseases, confirming an infection is generally not easily done when your pet walks into the vets; but rather, tends to require a couple of rounds of testing if the initial blood tests and urinalysis look suspicious. What raises suspicion of a Leptospira infection are elevated kidney and liver values, and sometimes the white blood cell count, too. If leptospirosis is suspected, your vet will usually recommend specific blood and urine tests, such as PCR testing or antibody testing, to confirm the diagnosis. In some cases, follow-up testing may be needed. Results can take several days, and so antibiotic treatment is often started based on suspicion, pending the results.

Thankfully, some dogs exposed to Leptospira may develop only mild or subclinical infections and show few or no obvious signs of illness. However, when dogs do develop clinical leptospirosis, the disease can progress rapidly and may become life-threatening.

Without immediate treatment, leptospirosis can lead to kidney failure, liver failure and even death. Blood or plasma transfusions are sometimes needed if your dog’s body loses its ability to clot due to liver compromise. Yes: this is one bad bug.

How can you keep you and your dog safe?

In general, it’s important to minimise your dog’s access to areas populated by rodents and farm animals to limit the risk of exposure. When walking with your dog in rural areas, when possible, watch out for areas heavily trafficked by wildlife. Keep your garden free of stagnant water and clean your home often – especially in areas where there is pet urine.

In cities, rats are harder to avoid, so steer clear of puddles and don’t let your pet drink from communal water bowls at parks or those put out by local businesses, as you don’t know how often the water is refreshed or bowl cleaned (thanks but no thanks). If your dog attends daycare, get your pet vaccinated – more on that below.

“Cases of leptospirosis tend to spike in the late summer and autumn, or, in cooler climates, during rainy winters,” says Ashley DiPrete. “Outbreaks tend to follow seasons with abnormally high rainfall or increased flooding.” So, since we’ve been experiencing high rainfall and flooding recently in the UK, now’s the time to be vigilant.

Do leptospirosis vaccines work?

Yes, leptospirosis vaccines used in the UK are effective at protecting dogs against the most common and clinically important strains of Leptospira found. These vaccines work by stimulating immunity against specific serovars of the bacteria. While no vaccine can protect against every strain of leptospirosis worldwide, vaccination significantly reduces the risk of infection and, importantly, the severity of disease if a dog is exposed. Immunity typically lasts around 12 months, which is why annual booster vaccinations are recommended after the initial course.

As with any vaccine, there is a small risk of side effects, so it’s important to discuss your dog’s lifestyle, environment, and individual risk factors with your vet. They can advise on whether leptospirosis vaccination is appropriate for your dog and which protocol best suits them.