Every Australian winter, cold, wet weather pushes rats closer to our homes, sheds and bins — and that quiet seasonal shift has helped an old, largely forgotten dog disease creep back into our cities. Leptospirosis was almost unheard of in Sydney pet dogs for decades, yet researchers at the University of Sydney confirmed 17 cases across Greater Sydney between 2017 and 2020, with a devastating 88% fatality rate. It is still uncommon, but it is serious, and it is largely preventable.
What leptospirosis actually is
Leptospirosis is a bacterial infection caused by Leptospira bacteria. According to the RSPCA Knowledgebase, small mammals such as rodents are the most common carriers and shed the bacteria in their urine. A dog usually becomes infected when its mucous membranes or broken skin contact infected urine, or contaminated soil and water — a puddle, a pond, a muddy backyard corner where rats have been active. Dogs that hunt or chase rats are at particular risk.
This is where the winter link matters. As the weather cools, rodents move in around homes and warm sheds, and standing water from winter rain keeps the bacteria alive in the environment for longer. That combination is exactly what drove the recent inner-Sydney clusters.
Symptoms every owner should recognise
Early signs are vague, which is part of what makes leptospirosis dangerous. The RSPCA and Sydney referral hospital SASH Vets list fever, lethargy, going off food, vomiting, diarrhoea, increased drinking and urination, and jaundice (a yellow tinge to the gums, skin or the whites of the eyes). Because the bacteria can attack the kidneys, liver and sometimes the lungs at the same time, a dog can go downhill fast.
| What you’re seeing | What to do |
|---|---|
| Mild off-day: slightly quiet, ate a bit less, otherwise bright | Monitor closely for 12–24 hours and phone your vet for advice |
| Vomiting, diarrhoea, not eating, drinking much more than usual | Book a same-day vet appointment |
| Yellow gums or eyes, collapse, laboured breathing, or barely producing urine | This is an emergency — go to a vet or emergency hospital now |
Is your dog at higher risk?
Most Australian dogs are low risk, but some clearly aren’t. The Greencross Vets guidance and the University of Sydney case series point to a few clear risk factors:
- Dogs that hunt, chase or dig for rats and mice
- Dogs that drink from or swim in puddles, dams, ponds or stagnant water
- Dogs living near waterways, bushland, farms or areas with heavy rodent activity
- Dogs in known hot-spots — the Sydney cases clustered in inner-city suburbs including Surry Hills, Darlinghurst, Redfern, Glebe, Newtown and Paddington, and cases have also been reported on the NSW Central Coast and coastal regions. Leptospirosis is most common in north-eastern NSW and Queensland, per NSW Health.
Prevention and the vaccine
There is a vaccine. Australia has one registered vaccine covering the strain behind the Sydney outbreak — Protech C2i (Boehringer Ingelheim), which targets serovar Copenhageni, as documented in the University of Sydney research. It is not part of the standard C3 core vaccination and is given as an optional extra, so you need to ask for it. The RSPCA notes at-risk dogs need two initial doses two to four weeks apart, followed by yearly boosters. Pricing varies between clinics — it is usually a modest add-on of roughly $30–$80 on top of your annual vaccination, but confirm with your own vet.
Vaccination aside, sensible everyday steps lower the risk: keep your dog on a lead near water and stop it drinking from puddles or ponds, control rats around the home, and don’t leave pet food out where it attracts rodents. Avoid loose rat and mouse baits, which are both a poisoning hazard and a sign of the rodents you’re trying to keep away. For how leptospirosis fits alongside your dog’s other shots, see our guide to the Australian vaccination schedule and costs, and for the wider winter picture, our winter parasite protection guide. Not sure where to start? Use the Australian Veterinary Association Find a Vet tool to locate a clinic near you.
Can people catch it too?
Yes. Leptospirosis is a zoonotic disease, meaning humans can be affected, as both the RSPCA and NSW Health confirm. People usually catch it through contaminated water or soil rather than directly from a pet, and human-to-human spread is very rare. In people it can cause sudden fever, headache and muscle aches. If your dog is diagnosed, practise good hygiene, wear gloves when cleaning up urine, and speak to your own doctor if you feel unwell. For more, the Better Health Channel has a plain-language overview.
The bottom line
- Leptospirosis is rare in Australian pet dogs but can be fatal, and winter rat activity raises the risk.
- Watch for fever, vomiting, jaundice and reduced urination — and act fast if you see them.
- A vaccine (Protech C2i) exists for at-risk dogs; ask your vet whether your dog needs it.
- It is zoonotic, so basic hygiene protects your household too.
Frequently asked questions
Is leptospirosis common in dogs in Australia?
No. It remains uncommon, and for most dogs the everyday risk is low. The concern is that when a dog does get it, the illness can be severe, so awareness and prevention matter more than panic.
Should I get my dog vaccinated against it?
It depends on your dog’s lifestyle and location. If your dog hunts rats, drinks from puddles, or lives in a higher-risk area, talk to your vet about the Protech C2i vaccine. It is not automatically included in core vaccinations.
Can my cat catch leptospirosis?
Cats can be exposed but rarely show serious illness and are considered far less susceptible than dogs. The vaccine is for dogs. If your cat is a keen hunter and seems unwell, see your vet.
How much does the vaccine cost?
Prices vary by clinic and region. It is generally a small add-on to your dog’s yearly vaccination rather than a major expense — your vet can give you an exact quote.
Written by Jessica Turner, a pet care writer at GoPetr. Jessica is not a veterinarian, and this article is general information only — it is not a substitute for professional veterinary advice. Every medical claim above is linked to an authoritative Australian source. If your dog is unwell, please consult a licensed veterinarian for diagnosis and treatment specific to your pet.
