Leptospirosis and Rat Season 2026: Why This Autumn Is the Right Time to Talk to Your Vet

What Leptospirosis Actually Is

Leptospirosis is a bacterial infection caused by Leptospira — a spirochete bacteria carried primarily by rats and mice. Infected rodents shed the bacteria in their urine, which then contaminates soil, puddles, and stagnant water. Dogs become infected when that contaminated water contacts their skin, mucous membranes, or any open wound — which can happen simply by splashing through a puddle or sniffing wet ground where a rat has passed. The organism can survive for up to two months in stagnant water if conditions are favourable.

Once inside the body, the bacteria cause severe damage to the kidneys and liver. The disease was characterised by severe hepatorenal involvement resulting in an unusually high case fatality rate of 88% in the original Sydney outbreak. Even with intensive veterinary care including intravenous fluids and antibiotics, the majority of affected dogs in Sydney did not survive.

It is also a zoonotic disease — meaning it can pass from animals to humans.

This Is a Surry Hills Story

Leptospirosis had not been reported in the Sydney dog population since 1976. When it re-emerged in 2017, it did so right here. Dogs infected between 2017 and 2019 lived within a 3 km radius in the inner city, with cases confirmed in Surry Hills, Haymarket, Redfern, Darlinghurst, Glebe, Newtown, and Paddington.

University of Sydney research specifically identified a significant primary cluster of canine leptospirosis in the suburbs of Surry Hills and Darlinghurst within a 1.1 km radius. When the cluster was adjusted for age, it expanded to cover Surry Hills, Darlinghurst, Chippendale, Eveleigh, and Redfern — precisely the suburbs that make up Vets on Crown's community.

The research also named the parks where infected dogs had been walking. The most frequented parks among seropositive dogs were Ward Park, Moore Park, Prince Alfred Park, Redfern Park, and a park in Woolloomooloo. These are the same parks where inner-city dogs go every day.

The connection is not coincidental. Vets on Crown was one of the veterinary practices that contributed cases to the original University of Sydney research that first characterised this outbreak in Sydney. This is a disease our team has seen first-hand.

Why Autumn Is the Riskier Season

The timing matters. As temperatures drop, rodents move indoors — into the terrace houses, laneways, apartment buildings, and restaurant back-of-house areas that line Crown Street, Bourke Street, and Cleveland Street. More rodents in urban spaces mean more contaminated urine in the environment. Autumn also brings more rainfall, which washes rodent urine into puddles, grass, and soil — exactly the environments dogs interact with on every walk.

This year, the risk is compounded by the new rat bait rules. The March 2026 APVMA restriction on second-generation anticoagulant rodenticides means stronger products are off supermarket shelves, and some residents may be less effective at controlling their rodent populations this winter. More rodents in the environment translates directly to greater leptospirosis exposure risk for dogs.

The biggest risk factor is exposure to free-standing water — puddles, ponds, slow-moving or stagnant water — especially where there is a rodent problem. After any rain in Surry Hills, Redfern, or Darlinghurst, this description covers almost every gutter, laneway, and park corner in the area.

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