Leptospirosis in Dogs: An Ontario Fall Risk and Why the Vaccine Matters

The call comes in more often than you’d expect once the leaves start to turn. A Burlington owner on the line, worried because their dog seems off after a soggy walk near a creek.

Maybe the dog drank from a puddle. Maybe it nosed a back corner of the yard where a raccoon visits after dark.

Fall in Halton brings warm, wet weeks and a lot of standing water. It also brings one of the questions our team on Brant Street fields most this time of year: does my dog really need the leptospirosis vaccine?

Leptospirosis is a bacterial infection dogs most often pick up from water contaminated with the urine of infected animals, especially stagnant puddles, ponds and lakes, according to Cornell’s Riney Canine Health Center. In Canada it clusters in the fall, when warm, wet weather helps the bacteria survive, reports a Canadian veterinary review.

If this is happening right now: If your dog is suddenly weak, vomiting, off their food, or their gums or eyes look yellow, don’t wait — call us at (905) 336-4002 or reach your nearest emergency veterinary hospital. After hours, our after-hours care page walks you through what to do.

How do dogs get leptospirosis?

Most dogs are infected through contact with urine-contaminated water, particularly stagnant or slow-moving water like puddles, ponds and lakes, says Cornell’s Riney Canine Health Center. The AVMA notes the bacteria usually enter through mucous membranes (the moist tissue of the mouth, nose or eyes) or through cuts and scrapes in the skin.

The Merck Veterinary Manual describes several routes: contact with contaminated urine or water, bite wounds or damaged skin, eating infected animals, and occasionally passage during birth. The same source notes the bacteria can survive for long stretches in surface water like swamps, streams and rivers.

Wild rodents are a major source through their urine, the AVMA adds, though they aren’t the only one. A dog lapping from a rain-filled dip in the grass at a Burlington park is doing the ordinary dog thing that can put it in contact with the bacteria.

Why is leptospirosis more common in the fall in Ontario?

In Canada, leptospirosis in dogs occurs largely in the fall, roughly September through December, when the weather is both warm and wet in a way that favours the bacteria’s survival, according to a Canadian veterinary review published in a peer-reviewed journal. Ontario data show the risk here has been climbing for years.

The same Canadian review links the rise to the large raccoon populations that thrive in cities and suburbs, plus a warming climate that helps the organism persist. Infected dogs can shed those bacteria in their urine for up to 6 weeks, the review notes, which keeps the cycle going.

An Ontario study of cases from 1998 to 2006 found a significant increase, with city dogs at clearly higher risk than rural dogs.

Source: Ontario seroprevalence study (NCBI/PMC). “Serovars” are the wildlife-associated strains the study tracked.

Conservation Halton monitors flooding across Halton watercourses and issues a Flood Outlook (early notice of possible flooding from heavy rain, snowmelt or high wind) and a Flood Watch (flooding possible in specific creeks or municipalities). Those wet-weather events leave standing water on low ground and roadsides that fits the exposure pattern exactly.

What are the first symptoms of leptospirosis in dogs?

The most common pattern begins with sudden-onset kidney disease, with signs like sluggishness, loss of appetite, vomiting, dehydration and back pain, according to the Merck Veterinary Manual. Cornell’s Riney Canine Health Center notes the incubation period, the time between exposure and first symptoms, is about one week.

Merck adds that the disease can also cause sudden liver failure, sometimes alongside kidney disease, which can lead to yellowing of the gums, skin and eyes. That yellowing is jaundice, a visible sign that the liver is struggling.

Severity varies widely. The updated ACVIM consensus statement, a national expert panel’s guidance, reports that leptospirosis remains common even in small-breed urban dogs and in puppies as young as 11 weeks, and that its most severe lung form, leptospiral pulmonary hemorrhage syndrome (bleeding in the lungs), has been linked with mortality of up to 70%.

This isn’t something to sort out at home. If your dog turns quiet, stops eating, or starts vomiting a few days after a wet walk, that’s a reason to call us and, in a serious case, to consider critical care.

Do city dogs get leptospirosis, or only rural and hunting dogs?

City dogs are absolutely at risk. The updated ACVIM consensus statement reports that leptospirosis stays prevalent in small-breed dogs from urban areas and in very young puppies, and an Ontario study found urban dogs at roughly 1.6 times the risk of rural dogs.

The reason ties back to wildlife. A Canadian veterinary review links the Ontario rise to the raccoons that flourish in urban and suburban neighbourhoods, shedding bacteria into soil, vegetation and standing water.

So the old picture of leptospirosis as a farm-dog or hunting-dog problem doesn’t hold up here. A small dog that never leaves a Burlington backyard can still cross paths with raccoon urine near a fence line or a puddle after an autumn storm.

Size and lifestyle don’t make a dog exempt, so the vaccine conversation applies right across Halton, not just to country dogs.

Is the leptospirosis vaccine necessary, and how often does my dog need it?

The updated ACVIM consensus statement recommends that all dogs be vaccinated against leptospirosis every year starting at 12 weeks of age, regardless of breed, because it’s a zoonotic disease (one that can pass between animals and people), can be severe or fatal despite treatment, and can be caught regardless of age, geography or lifestyle.

Does it work? A meta-analysis cited in that consensus statement found leptospirosis vaccines give over 80% protection against clinical disease and against a dog becoming a kidney carrier, with protection lasting at least 12 months.

The same source confirms the inactivated (killed-bacteria) vaccines don’t cause the disease. The AVMA describes the usual schedule as an initial series of two vaccinations spaced 4 weeks apart, followed by annual boosters.

Sources: ACVIM consensus statement and AVMA. Your dog’s plan can fold into a routine wellness and vaccination visit, so protection is current before the fall risk window.

Can I catch leptospirosis from my dog?

Leptospirosis can spread from dogs to people, so it’s worth taking seriously, but the day-to-day risk to a household is low. The AVMA says an infected dog is unlikely to infect you and your family, though there’s still some risk, and it advises washing your hands after handling your dog and avoiding contact with its urine.

Infection can also linger. The Merck Veterinary Manual notes that surviving dogs can become carriers, harbouring the bacteria in the kidneys and shedding it in urine for months or even years.

Wildlife is the bigger everyday exposure for most families. Halton Region Public Health advises residents to observe wildlife from a distance, to not touch, feed or move wild animals, and to keep pets up to date on their vaccinations.

Common-sense steps go a long way. Rinse muddy paws, keep your dog from drinking standing water, and tell us if anyone at home is pregnant or immune-compromised.

How is leptospirosis diagnosed and treated, and can dogs recover?

Leptospirosis is treated with antibiotics, most commonly doxycycline, for at least two weeks, and many dogs do recover, according to Cornell’s Riney Canine Health Center. Cornell also cautions that some dogs which survive may be left with chronic kidney or liver disease.

Diagnosis usually takes more than one test. The Merck Veterinary Manual recommends combining acute and convalescent MAT titres (an antibody blood test run twice over time) with PCR assays (which detect the bacteria’s DNA) on blood in early disease or urine later on.

Merck notes doxycycline at 5 mg/kg every 12 hours for two weeks, a course that also clears the carrier phase so a recovered dog stops shedding bacteria. Severe cases often need supportive hospital care too.

Early action matters. If leptospirosis is on the table, getting the right diagnostics started quickly gives your dog the best shot at a full recovery.

This article is educational and isn’t veterinary advice or a substitute for an exam. If you’re worried about your pet right now, call us at (905) 336-4002 or your nearest emergency veterinary hospital.

If it’s coming up on fall and you’re not sure your dog’s leptospirosis vaccine is current, that’s an easy thing to check. We’re happy to look at the record and get the timing right before the wet-weather season.

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Frequently asked questions

Can a fully indoor or small-breed dog still get leptospirosis?

Yes. The updated ACVIM consensus statement reports leptospirosis stays common in small-breed dogs from urban areas and in puppies as young as 11 weeks. A little dog that only uses a Burlington backyard can still contact raccoon urine near a fence, garden or puddle, so size and lifestyle don’t make a dog exempt.

Can dogs fully recover from leptospirosis?

Many do. Cornell’s Riney Canine Health Center says leptospirosis is treated with antibiotics, most commonly doxycycline, for at least two weeks, and dogs often recover with prompt care. Cornell also notes some survivors may be left with chronic kidney or liver disease, which is why early treatment and follow-up monitoring both matter.

Does the leptospirosis vaccine give my dog the disease?

No. The updated ACVIM consensus statement confirms that the inactivated, or killed-bacteria, leptospirosis vaccines do not cause the disease. The same source, citing a meta-analysis, found the vaccines give over 80% protection against clinical illness and against a dog becoming a kidney carrier, with protection lasting at least 12 months.

How long does the leptospirosis vaccine protect my dog?

Current leptospirosis vaccines protect for at least 12 months, according to a meta-analysis cited in the updated ACVIM consensus statement, which is why the panel recommends annual boosters. The AVMA describes the usual plan as two initial doses spaced 4 weeks apart, then a booster every year to keep protection from lapsing.

My dog drank from a puddle on a fall walk. What should I do?

Don’t panic, but do keep an eye on your dog. Cornell notes the incubation period is about one week, so watch for sluggishness, appetite loss, vomiting or yellowing of the gums or eyes over the following days, and call us if any of that shows up. If you’re worried, we’re glad to talk it through.

Is there a best time to make sure the vaccine is current?

Because Canadian data show cases cluster in the fall, roughly September through December, it makes sense to check your dog’s record before that window. Booking a wellness visit in late summer or early fall gives protection time to be in place. Our team on Brant Street can confirm the timing anytime.

Sources

Veterinary medical references

1. Merck Veterinary Manual, Leptospirosis in Dogs (Dog Owners). https://www.merckvetmanual.com/dog-owners/disorders-affecting-multiple-body-systems-of-dogs/leptospirosis-in-dogs
2. Merck Veterinary Manual, Leptospirosis in Dogs (Infectious Diseases, clinical). https://www.merckvetmanual.com/infectious-diseases/leptospirosis/leptospirosis-in-dogs
3. Cornell University Riney Canine Health Center, Canine Leptospirosis. https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-topics/canine-leptospirosis
4. American Veterinary Medical Association (AVMA), Leptospirosis (pet owners). https://www.avma.org/resources-tools/pet-owners/petcare/leptospirosis

Peer-reviewed research

1. Updated ACVIM Consensus Statement on Leptospirosis in Dogs (NCBI/PMC). https://pmc.ncbi.nlm.nih.gov/articles/PMC10658540/
2. Canine leptospirosis in Canada: a veterinarian’s perspective (NCBI/PMC). https://pmc.ncbi.nlm.nih.gov/articles/PMC2228365/
3. Increase in seroprevalence of canine leptospirosis and its risk factors, Ontario 1998-2006 (NCBI/PMC). https://pmc.ncbi.nlm.nih.gov/articles/PMC2705070/

Local and public health

1. Conservation Halton, Flood Status. https://www.conservationhalton.ca/flood-status/
2. Halton Region Public Health, Protecting your family and pets. https://www.halton.ca/for-residents/immunizations-preventable-disease/rabies/protecting-your-family-pets-against-rabies