The worst disease you’ve never heard of – warning over rat lungworm disease

A parasite behind a disease that has claimed two human lives is infecting an increasing number of dogs in eastern Australia, and researchers say the rise could be driven by heavy rainfall.

Female adult rat lungworms are on the rise in eastern Australia in dogs – and there have even been recorded cases in humans, including two known lethal incidents. Picture: Supplied

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People have been warned about worsening conditions for the spread of the horribly named and potentially deadly rat lungworm disease.

The parasite behind the disease, which has claimed two human lives, is infecting an increasing number of dogs in eastern Australia, and researchers say the rise could be driven by heavy rainfall.

Sydney School of Veterinary Science professor Jan Slapeta and his team analysed five years of data to identify the high-risk period for transmission of the disease – between two and 10 months after heavy rainfall.

In 2022, following La Nina, there was a peak in dog cases of rat lungworm.

“(The disease is) associated with heavy downpours and a large amount of water that falls from the sky,” Professor Slapeta said. “It’s a perfect breeding ground for these slugs and snails.

“More rain, more slugs, meaning unfortunately more rat lung disease.”

Infective larva of rat lungworm. Caused by a parasite naturally found in rats, the disease requires ongoing monitoring to ensure it is controlled and doesn’t pose a public health threat. Picture: supplied

Because of these weather trends, Professor Slapeta said May and June were the riskiest times for contracting the disease.

The lungworm itself is of little danger to a human host; it is the body’s response to the foreign parasite that causes harm.

“This parasite for some reason wants to go into the brain and spinal cord, and once it’s there the host recognises that there is a worm,” Professor Slapeta said. “They start to put all the effort and immune response that the body has got into it and that causes inflammation.

“Immediately the brain swells, the spinal cord swells, which leads to headaches, meningitis and all the symptoms of being potentially paralysed.”

He said if the human allowed the parasite to “go through the motions through the brain” it likely would leave and die somewhere else. The parasite is common in the rat population but is transmissible only through slugs or snails that have consumed faeces from an infected rat.

Since the 1970s there have been at least 12 recorded cases of rat lungworm in Australia, including two fatalities – most significantly the case of Sam Ballard, who died in 2018 after an eight-year illness contracted after consuming an infected slug.

Professor Slapeta said toddlers who crawled in backyards and ate dirt could ingest a snail or slug. The disease is not transmissible from animal to person or person to person.