Cases of the grimly named and potentially devastating rat lungworm disease are on the rise in eastern Australia, posing a serious threat to humans.

A study published this week by veterinary scientists at the University of Sydney warns that climate change and the resulting fluctuating weather could be behind the troubling rise.

Rat lungworm disease, also known as neural angiostrongyliasis, has spread from its origins in South-East Asia to Australia, as well as North America and Europe.

Naturally found in rats scavenging in our cities, the parasite that causes the disease is transmitted through snails and slugs.

Once in humans or dogs, the worms quickly get to the brain, where they cause disease.

“These snails and slugs, and the infective worm larvae in them, can – accidentally – be a disease source to us humans and our pet dogs,” said Professor Jan Šlapeta from the Sydney School of Veterinary Science. 

Šlapeta is senior author of a paper examining the spread of the disease published this week in The Journal of Infectious Diseases.

Rat lungworm disease is caused by the parasite Angiostrongylus cantonensis, which is naturally found in rats.

Humans and dogs are considered accidental hosts, and infection can lead to devastating neurological consequences.

“In dogs and humans, the parasite enters the brain but rather than progressing to the lungs like it does in rats, it is killed in the brain by our own immune response,” lead author Phoebe Rivory said.

“It is that overt immune response that causes severe headaches and sensations.”

Life cycle of the rat lungworm. Photo: University of Sydney

One of the most high-profile Australian cases of rat lungworm diseas in recent years resulted in the tragic death of Sydney man Sam Ballard.

In 2010, Ballard swallowed a garden slug as part of a prank with friends.

As a result he contracted encephalitis and was plunged into a coma for 420 days. Doctors later determined Ballard was infected with rat lungworm.

When he regained consciousness, but suffered significant brain injuries. He lived for another eight years before his death in 2018.

It is estimated there have been at least half a dozen recorded cases in humans since the 1970s in Australia, including at least one other fatal incident.

Sam Ballard contracted rat lungworm after swallowing a slug. Photo: Facebook/Getty

The University of Sydney scientists drew a link between climate-changed induced weather fluctuations and the troubling spread of the disease.

The group developed a model that identifies high risk periods for transmission of the disease between two and 10 months after heavy rainfall.

The scientists identified 93 cases in dogs in the study period, with a peak of 32 in 2022. This peak was due to high rainfall, a driver of snail and slug proliferation.

“This is another example how the La Niña events with wetter than average periods in Australia lead to increased disease transmission and occurrence,” Šlapeta said.