A combination of rats, rain and stagnant water is raising the risks of a disease that can be deadly for dogs. Veterinarian Dr Sarah Foo, from Austinmer Veterinary Hospital, explains what Leptospirosis is and what we can do to protect our pets.

What is Leptospirosis?

Leptospirosis is a bacterial disease that affects a variety of mammals that includes dogs and humans. It is caused by a bacteria called Leptospira, and has a lot of different serovars. Serovars are a specific subtype of microorganism, like a bacterium, that are distinguished by their different antigenic properties.

Leptospirosis is a zoonotic-based disease, which means humans can contract it.

“There have been cases where dogs have transmitted leptospirosis to their owner but thankfully not any of the cases we have seen in NSW yet,” Sarah says.

What are some of the symptoms of Leptospirosis?

• Vomiting
• Diarrhoea
• Lethargic
• Excessive urination and drinking
• Inability to urinate

“The biggest concern is that some of the symptoms can be nonspecific but as the disease progresses you can see more severe signs, like kidney and liver diseases, which can be fatal,” Sarah says.

“Even dogs that survive the infection can have longer-term kidney and liver disease, which can shorten their lifespan.”

What are the causes of Leptospirosis?

Leptospirosis is generally passed on in the urine of rats and livestock like cattle, and can be more common in farm areas. A combination of lots of rats and rain, can also increase the spread of leptospirosis.

Leptospirosis can be anywhere, especially where there is stagnant water.

“Things like puddles, lakes, streams that don't have much movement, communal dog water bowls in the parks where no one's necessarily cleaning them regularly.

“It would just take one rat to urinate in that body of water to contaminate it.”

Sarah says vets are starting to see Leptospirosis spread in areas they haven’t seen before.

“We saw very low case numbers for a really long time and vaccination rates dropped off. Then from 2017 we started seeing cases again, starting in the inner city with two major outbreaks in 2022, in Shoalhaven and Lake Macquarie, with cases seen in over 70 suburbs in NSW in the last few years,” Sarah says.

Suburbs in or near to the Illawarra where cases have occurred are Albion Park, Kembla Grange, Shoalhaven, South Coast and Southern Highlands.

In June 2025, four cases were reported in NSW: in the Shoalhaven's Erowal Bay, Bundanoon in Wingecarribee Shire, Newcastle and Hinton in Port Stephens. 

“Unfortunately, all four patients who contracted Leptospirosis in June this year passed away. Three were not vaccinated, and the vaccination status of the last was unknown,” Sarah says.

Leptospirosis can also be caught by a dog contacting grass that a rat has urinated on and licking its paws afterwards.

As dogs become infected, they become carriers of the disease, and with many people travelling on holidays with their dogs, leptospirosis can easily spread to various areas.

What are ways to prevent Leptospirosis?

Vaccination is one the best ways to your dog protected from leptospirosis.

"It's one of those diseases that when they do get infected, they can get sick really quickly and it can become fatal. Treatment can be intense, and expensive and depending on the severity of disease, may have varying success, so prevention is key.”

Currently there are two vaccines available, with one most commonly used only covering one strain of leptospirosis. Recently a newer vaccine became available which covers multiple serovars, including the most common serovar currently affecting dogs.

“Once they receive the first shot, they receive a booster, two to four weeks later, and we encourage all people with puppies to vaccinate for it so it becomes a part of their annual vaccinations,” Sarah says.

Adult dogs that haven’t had any vaccines for leptospirosis need to have two vaccinations: one initial vaccination and a booster shot two to four weeks later.

It’s important to note that the leptospirosis bacteria have the ability to mutate and change.

Dogs that have come into contact with a dog that has leptospirosis may be put on a treatment to prophylactically to stop them from developing symptoms. It is also recommended that any humans that have been in contact with cases go to their local healthcare provider as soon as possible for advice.

“Dogs that have leptospirosis need to be isolated with vets and nurses trained in barrier nursing who are in full PPE, i.e. gowns, masks and gloves, making sure there's no potential risk of exposure to humans or other animals,” Sarah says.

Dogs that have a prey drive can be more prone to chase things, including rats, increasing their risk of contracting leptospirosis, Sarah says.

“A recent 2025 study showed terriers, dogs bred for ratting, working and herding dogs that like to chase things and younger, inquisitive dogs who like to explore or swim in and drink from puddles, can be at a higher risk of exposure.”

Environmental measures like pest control, fencing, clearing puddles of water that can become stagnant, help reduce leptospirosis. One of the best ways to reduce leptospirosis is clearing pools of water, even raised water sources, as arboreal species can urinate into them which is difficult to stop.

Vaccination availability depends on the veterinary clinic, so it is important to know which veterinary practices offer it.

Dr Sarah Foo works at Austinmer Veterinary Hospital, which offers the newest leptospirosis vaccination, and shares updates on Facebook