Killer snails, alarm goes off in Australia: they are killing dogs but also posing a risk to humans

There is alarm in Australia over the rapid spread of the so-called 'killer snail' or rat lungworm. Angiostrongylus cantonensis is a parasite that has caused concern among thousands of pet owners. Rat lungworm is spreading rapidly and killing dogs, especially in Sydney and Brisbane. According to new research from the University of Sydney , 93 cases were confirmed between 2020 and 2024, many of which involved animals dying or becoming paralyzed after ingesting infected snails or slugs.

The issue is causing concern among doctors and health authorities because, although rare, the disease is potentially lethal for humans. It is transmitted by the larvae of the parasite present in wild rats. The latter are expelled through the feces of rodents and ingested by snails and slugs, which become intermediate hosts. When a dog ingests them, even accidentally, it can become infected and develop serious neurological symptoms. In some cases, the consequences are irreversible. The parasite is not contagious from person to person.

The risk of meningitis for humans

"Giant snails, originally from Africa - explains Matteo Bassetti, director of Infectious Diseases at the Policlinico San Martino in Genoa - are capable of transmitting the parasite that is dangerous for human health, as it affects the pulmonary tract and can lead to severe meningitis. The recent heavy rains have favored its spread, especially between Sydney and Brisbane - Angiostrongyliasis is an infection of growing importance for public health, as globalization contributes to the geographical spread of the disease". Now, the expert explains, it is necessary to "continue working together with the various countries of the world to monitor the situation".

The infection, considered rare but potentially fatal, has been found in a small but growing number of dogs in areas affected by heavy rainfall, and occasionally in humans. Between 1971 and 2018, 28 human cases were documented in Australia. The best-known case was that of Sam Ballard , a young rugby player from Sydney, who in 2010 accepted a dare from friends and ate a garden snail. He contracted the parasite, fell into a coma for 420 days and battled severe brain damage for eight years, until his death in 2018 at the age of 28.

The rat lungworm

The rat lungworm, or Angiostrongylus cantonensis, is a parasite that originated in Southeast Asia but has spread to other parts of the world, including North America, Europe, and Australia. The parasite's natural host is wild rats, but it can accidentally make its way to other animals through a complicated transmission process involving snails and slugs as intermediate hosts.

The symptoms

When it finds its way into humans and dogs, rat lungworm can cause a disease called neural angiostrongoliasis. In humans, it is diagnosed as a type of meningitis or eosinophilic meningoencephalitis.

Symptoms in humans include headache, a stiff neck, tingling or sore skin, fever, nausea, and vomiting. In rare cases, it can cause permanent brain damage or be fatal, especially in people with compromised immune systems.

In dogs, the disease leads to paralysis, urinary incontinence, and abnormal pain responses. The time between eating an infected snail and becoming ill is usually one to three weeks. Both humans and dogs can become ill if they eat a raw snail carrying larvae, or unwashed vegetables, such as lettuce, contaminated with infected slime.

The brain

University of Sydney PhD researcher Phoebe Rivory , an author of the recent study, explained that it is not the parasite itself that does the damage, but the body’s attempts to fight it. “In dogs and humans, the parasite enters the brain, but rather than progressing to the lungs as in rats, it is killed in the brain by our own immune response. It is that overt immune response that causes severe headaches and sensations,” Rivory explained. New South Wales Health says it is rare for humans to develop meningitis in response to rat lungworm, and most people who get it have no symptoms at all, while others may only have mild, short-lived symptoms.

Why are cases increasing?

Researchers at the University of Sydney looked at the prevalence of the disease in dogs based on the fact that they are a sentinel population for humans. This means that rising rates of the disease in dogs could be an early warning sign of the risk of human disease. The researchers analysed 180 clinical samples taken between 2020 and 2024 from dogs suspected of having had the disease and confirmed 93 cases, all in or around Sydney and Brisbane, with a “gradual upward trend”. They also found a spike of 32 cases in 2022, which correlated with high levels of rainfall, which tends to supercharge snail breeding.

Prevention

Health authorities recommend preventive measures, including washing fruits and vegetables thoroughly; preventing dogs from ingesting snails, slugs or wet grass in parks after rain; and avoiding direct contact with snails or frogs, especially in rural or tropical areas.