Leptospirosis is a bacterial infection spread primarily through the urine of infected animals — rats above all, but also mice, cattle, pigs and wildlife.
The bacteria survive for weeks in warm, wet, stagnant conditions, and dogs pick them up by drinking from or swimming in contaminated water, or through cuts and mucous membranes.
It causes kidney and liver failure, it can be fatal, and it is transmissible to humans.
Where dogs pick it up
- Standing water — puddles, ditches, ponds, slow streams
- Muddy ground and flooded areas
- Farmland and areas with livestock
- Anywhere with a rat population — including urban parks, canals, waterways and allotments
- Warm wet weather, which is when risk peaks
Country dogs and city dogs both get it. Canal towpaths and urban parks with water features are not low-risk environments.
The signs
Variable, which is part of what makes it difficult. They range from mild and self-limiting to fulminant and fatal.
Common:
- Fever
- Lethargy and weakness
- Loss of appetite
- Vomiting and diarrhoea
- Increased thirst and urination, or reduced or absent urination as the kidneys fail
- Muscle pain, reluctance to move, a stiff gait
- Jaundice — yellowing of the gums, eyes or skin
- Dehydration
Severe:
- Acute kidney failure
- Liver failure
- Bleeding disorders — nosebleeds, blood in vomit or stool, pinpoint haemorrhages on the gums
- Pulmonary haemorrhage, which is often fatal
- Collapse
Any dog who is off colour with a fever after being in or near water deserves mention of that history to your vet. It genuinely changes the differential list.
Diagnosis and treatment
Blood and urine tests, including specific antibody testing and PCR. Because antibody titres rise over time, paired samples a couple of weeks apart are sometimes needed — which is why treatment often starts on suspicion.
Treatment: antibiotics, intravenous fluids, and supportive care for kidney and liver failure. Severe cases need intensive care, and some require dialysis where it is available.
Prognosis depends heavily on how quickly treatment starts and how much organ damage has occurred. Many dogs recover, some with lasting kidney damage; severe cases have significant mortality.
Vaccination
The main defence, and worth understanding properly.
It is a non-core vaccine in most protocols — meaning it is recommended based on risk rather than universally — but in many regions the risk is high enough that it is effectively standard.
Key points:
- Annual boosting, unlike core vaccines. Immunity is shorter-lived
- Multiple serovars. The bacterium has many strains, and vaccines cover a selected group. L2 vaccines cover two serogroups; L4 vaccines cover four, reflecting strains that have become more prevalent in parts of Europe
- It does not cover every strain, so a vaccinated dog can still, rarely, become infected — usually with milder disease
- Puppies need an initial course of two doses, typically two to four weeks apart
The L2 versus L4 question is worth asking your vet about, based on what is circulating in your area. There was a period of public concern about L4 safety, largely driven by online campaigning; regulatory reviews found the adverse event rate in line with other vaccines. Discuss it with your vet rather than a forum.
Risk reduction beyond vaccination
- Do not let dogs drink from puddles, ditches or stagnant water. Carry water
- Avoid swimming in slow or standing water, particularly in warm weather
- Control rodents around the home, garden, outbuildings and food storage
- Store dog food in sealed containers, which reduces rodent attraction
- Clear standing water in the garden
- Be cautious after flooding
Some links on this page are affiliate links. If you buy through them we may earn a small commission at no extra cost to you — it helps keep this site free. We only recommend products we would use with our own dogs.
PupFlask Dog Water Bottle
The practical version of “do not let them drink from puddles” is having something better available. A bottle with an attached bowl in the car and in your bag removes most of the temptation.
IRIS USA Airtight Pet Food Storage Container
Sealed food storage is a rodent-control measure as much as a freshness one. An open bag of kibble in a shed or garage is an invitation.
The human risk
Leptospirosis is zoonotic. In people it causes flu-like illness, and in severe cases — Weil’s disease — liver and kidney failure.
If your dog is diagnosed:
- Wear gloves handling urine, and clean contaminated areas with a diluted bleach solution
- Wash hands thoroughly
- Keep the dog away from children and immunocompromised people while shedding
- Follow your vet’s advice on how long they remain infectious after starting antibiotics
- Tell your own doctor if you develop flu-like symptoms, and mention the dog
Infected dogs can shed bacteria in urine for weeks or months after recovery, which is why the antibiotic course matters and why completing it is not optional.
Who is most at risk
- Dogs who swim in fresh water
- Working and farm dogs
- Dogs walked in areas with rats — which is most areas
- Hunting dogs
- Dogs who drink from puddles habitually
- Dogs in flood-prone regions
Which covers a very large share of pet dogs, and is why “we only walk in the park” is not a reason to skip it.
The short version
Ask your vet two questions at the next appointment: is lepto vaccination recommended here, and which vaccine are we using and why.
Then carry water on walks, and do not let your dog drink out of the puddle.
