Floods, heavy rain and rodents linked to rise in human cases of the bacterial disease leptospirosis

Leptospirosis cases have risen across pets and humans with recent floods, rain and an increase in rodent populations. This is what you must look out for.

Floods, persistent heavy rain and an increase in rodent populations have been linked to a rise in the number of leptospirosis cases in humans.

According to the National Notifiable Diseases Surveillance System (NNDSS) there have been 205 reported cases of leptospirosis in Australia in the 12 months from May 2 last year.

This is well above the yearly rolling five year mean of 148 cases, the data reveals. The bulk of cases have been in NSW and Queensland, the states hit hardest by the floods, first in March and again in April.

Leptospirosis is caused by leptospira bacteria, which is found in urine from infected animals including rats, mice, cattle, pigs, native animals such as possums, feral pigs and domestic animals include dogs, cats and horses.

Feral pigs can carry leptospirosis.

While there is a vaccine for dogs, pigs and cattle, there is no human vaccine, although the disease is easily treatable with antibiotics.

The bacteria can enter the body through skin cuts or abrasions or through the lining of the mouth, nose, and eyes by exposure to water, soil or mud contaminated with the urine from infected animals. Water affected by heavy rain or flooding is especially risky.

Case numbers began rising last year, prompting Queensland Health spokesperson Professor Keith McNeil to remind the community that while agricultural workers were at the highest risk, they were not the only ones.

“That means people who participate in camping, gardening, bushwalking and water sport pursuits can also be at risk of infection as they may have contact with contaminated water, soil or mud during these activities,” he said

“There are many different strains of the leptospira bacteria, so it’s possible to be infected with leptospirosis multiple times.”

The northern NSW town of Lismore was decimated by floods in March and April.

Professor McNeil said symptoms of leptospirosis may include fever, severe headache, muscle aches, chills, vomiting, and red eyes, and usually develop after five to 14 days following exposure.

“Symptoms can be similar to the flu so often it can be difficult to recognise and can be mistaken for other diseases,” he said.

High mouse numbers, including plagues in some parts of Australia, have also been blamed for the rise in leptospirosis cases.

The Federal Department of Health has produced a video featuring deputy chief medical officer Dr Sonya Bennett that provides advice specifically for Australians affected by mouse plagues and infestations.

“Mice can carry a number of bugs like bacteria which can cause diseases that affect human health but the main one that we are concerned about is leptospirosis,” she said.

She said the disease varied in severity from person to person, and early diagnosis was key. Left untreated it can become a serious problem.

“Some people have no symptoms at all,” Dr Bennett said.

“In rare situations, untreated leptospirosis may cause severe complications affecting the body’s major organs and may require hospitalisation, so it’s important to know what to look for.”

Australia’s deputy chief medical officer Dr Sonya Bennett. Picture: NCA NewsWire/Gary Ramage

After a person is exposed to the bacteria, symptoms usually start within five-14 days, but can range from two to 30 days.

The illness generally lasts from a few days to three weeks but can last longer.

“It’s important to speak to your doctor if you are concerned about your health or feel unwell,” Dr Bennett said.

“Let them know if you think you may have been exposed to leptospirosis through mice, or items contaminated with mice, including muddy ground. This will help speed up your diagnosis and ensure you receive appropriate medical care as soon as possible.”

The best way to avoid getting sick was to follow a good hygiene routine, and this was especially important when handling mice or items that have been contaminated by mice.

“It’s also important not to wade or swim in potentially contaminated water sources, such as dams, creeks or rivers, particularly if they are impacted by flood events,” she said.

Leptospirosis case numbers in dogs have also been rising in city and metropolitan areas in the past five years. An article published in the May Australian Veterinary Journal examined 17 cases in Sydney between 2017 and 2019. The affected dogs all lived within 3km of the city.

It was the first time canine leptospirosis had been reported in the Sydney dog population since 1976.

By 2020, the virus had spread further than the city, with cases reported in the Inner West, the Lower North Shore, the Upper North Shore and the Northern Beaches.

In another journal article, published in PLoS Neglected Tropical Diseases in January this year, researchers looked at infections in humans and dogs in North Queensland, an area known to be popular for feral pig hunters and their dogs.

Feral pigs are known carrier of the disease, the researchers wrote.

“Leptospirosis is an emerging disease of growing significance,” the researchers said.

“The infection requires a ‘one health’ approach to understand its epidemiology. With shifting climatic patterns influencing human-animal-environment interactions, ongoing monitoring of diseases like leptospirosis is critical to helping prevent infection of individuals and disease outbreaks.”

Originally published as Floods, heavy rain and rodents linked to rise in human cases of the bacterial disease leptospirosis