Brain worm spike detected in Australia following extreme weather event

Yahoo

17-06-2025

A tiny parasite that can infect human brains has the potential to change our way of life in Australia, threatening not only our health but what we eat. Originally from Southeast Asia, rat lungworm is now established along our east coast, with infections found as far south as Jervis Bay.
University of Sydney research has linked spikes in infections of the worm in animals to heavy rainfall, because the worm is commonly found in slugs and snails that proliferate during wet weather. A study of 93 dog infections in Sydney and Brisbane found 32 occurred directly after a single rain event, which were likely triggered after pets came into contact with common garden molluscs. The researchers found risk was elevated for between two and 10 months after heavy rain.
The study's senior author, Jan Šlapeta from the Sydney School of Veterinary Science, told Yahoo News it's unclear how far south the parasite will spread. But with the world's weather becoming warmer and wetter, it's possible it could one day make its way down to Melbourne.
"It has the potential to spread further. An indicator is that 20 or 30 years ago, we did not talk about it in America or Europe. Now it's in the southern states of the United States, it's creeping into Europe, it's in Spain," he said.
"I think climate change is very much helping this parasite spread further."
Interactions with slugs and snails are the most common way for people to become infected, either by accidentally or intentionally eating them, or by consuming unwashed salad they've had contact with. In 2010, a Sydney man died after he ate a slug following a dare.
It's unusual for anyone in Australia to eat an infected snail because of their large size, but that could change if there's a similar biosecurity breach to what has occurred in Hawaii.
It's on the Big Island that a tiny semi-slug,Parmarion martensi, has invaded the landscape. It's so small that it's easy to accidentally consume when eating salad greens and fresh fruit and vegetables.
"You can't wash them off or see them. The number of human cases [of rat lungworm] have increased dramatically," Šlapeta said. "In Australia we do not have this semi-slug. Is there a potential? We can't yet tell. But we have areas up north that are similar to Hawaii. I don't want to be an alarmist, but this parasite could create more havoc.
"If this semi-slug comes in, then it might end up on the veggies that people have got in their backyards. And that would change the landscape of this disease completely, like it changed in Hawaii."
The semi-slug would complete a cocktail of invasive species that Šlapeta doesn't want to see become established in Australia.
"The parasite is invasive, the rat is invasive, the European slugs that we see in the backyards of Sydney are invasive, but if we bring in the semi-slug... it could change the way we grow greens and behave in restaurants," he said.
The first sign the worm has reached a city is usually that animals in its zoo have become sick, with curious primates often picking up slugs inside their cage and then becoming sick. Reports made by wildlife rescue volunteers are also useful in monitoring its spread, as tawny frogmouths and possums often get sick in large numbers.
Since rat lungworm, also known as Angiostrongylus cantonensis, was first detected in Brisbane in the 1970s, at least six people have been infected, two of whom have died.
When it comes to infections in people, most are asymptomatic, and many cases likely aren't diagnosed.
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During its first phase of life, rat lungworm larvae hatch in the lungs of rats and is then passed through the animal as faeces. Slugs and snails consume that faeces and the worms grow inside of them. Rats then eat the slugs and snails and the process begins again.
The process is relatively harmless to slugs, snails and rats, but in other hosts like humans, dogs or native birds and mammals, the body can overreact and try to kill the parasite. On rare occasions, it causes an infestation in the brain that triggers an immune response that causes inflammation. Symptoms normally set on between one and three weeks after a slug or snail is eaten, and include headaches, nausea, vomiting, a stiff neck, pain in the skin and fever.
The University of Sydney study on rat lungworm infections in dogs advocates for a One Health approach to combating the parasite.
This concept means recognising that animals and humans live in the same environment and are therefore interconnected. But how best to respond to the problems it's causing is something that's left Šlapeta stumped.
"That's the million dollar question. The parasite is moving wherever it wants," he said. "We can't eliminate rats, we can't eliminate slugs, so we just have to be more vigilant around the clinical signs in our pets and ourselves.
"But there's not much we can do about tawny frogmouths. They will keep looking for some sort of food, and if the slug or snail is infected then they will become infected too."
The lead author of the study into rat lungworm in dogs was Sydney University's Phoebe Rivory. The research was published in the Journal of Infectious Diseases.
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