Slugs, snails are not alone in causing rat lungworm disease in humans

More than a dozen different types of animals have been linked to rat lungworm disease, according to a review of decades of research.

Researchers from the University of Hawai'i at Mnoa and the University of London combed through nearly 140 scientific studies published between 1962 and 2022. 13 species of prawns, crabs, flatworms, fish, frog, toads, lizards, and centipedes have been associated with causing rat lungworm disease in humans.

The thesis was part of a graduate program in One Health run by the Royal Veterinary College and the London School of Hygiene and Tropical Medicine. Robert Cowie was the senior author on the study and a faculty member in the UH Mnoa School of Ocean and Earth Science and Technology. Mark Fox is a professor at the Royal Veterinary College.

Cowie explained that the rat lungworm has a complex life cycle that involves slugs and snails as so-called "intermediate" hosts and rats as "definitive" hosts. Rats become sick when they eat food with an infectious bug. This can lead to serious illness and sometimes death, and people get infections when they eat snails or slugs.

Humans are accidentally hosts.

Cowie said that people can get infections if they eat paratenic hosts, which are also known as carrier hosts. The worms can't develop to maturity as they do in a rat, so these are animals that have been bitten by snails or slugs. The worms are stillfective in such hosts. Development can continue but only up to a point if one of these hosts is eaten raw by a person.

They are in the person's brain when they are feeding and growing. The worms don't last long. The symptoms of rat lungworm disease are caused by the damage to the brain and massive inflammation that occurs when they die.

Cowie said it's important to know which animals can transmit rat lungworm parasites to humans and which can't. The goal of the study was to pull all the information on paratenic hosts and their role in transmission of rat lungworm disease, previously scattered in diverse publications and obscure reports, together into a single place and develop a global understanding of their diversity and role in disease transmission.

There is a disease called rat lungworm.

South and Southeast Asia, southern China, Taiwan, southern Japan, various Pacific islands and archipelagos, and more recently Brazil, Caribbean islands, and Australia are where rat lungworm disease is found. In addition to the Canary Islands and Balearic Islands of Spain, there have been a few cases of rat lungworm disease in the United States. It is possible that climate change will lead to its further spread into cooler areas.

The University of Hawai'i and the US government discovered a connection between the parasites and the disease in the early 1960s.

Flatworms, centipedes, coqui frog, and cane toads are some of the species that can act as carriers. People in Hawai'i aren't likely to eat these animals, but it's not unusual for people to do so on a dare and get sick. Frogs and lizards are eaten for health reasons in Taiwan and Japan.

The rat lungworm parasites can also be found in domestic animals, such as dogs and horses.

It is possible to prevent infections.

There are a number of things people can do to prevent infections.

Cowie said that "awareness of which species may harbor the parasites is critical both in Hawai'i and more widely." They should not be eaten raw. All fruits and vegetables should be washed under running water and inspected for slugs, snails and flatworms so that they don't get eaten.

More information: Helena C. Turck et al, Paratenic hosts of Angiostrongylus cantonensis and their relation to human neuroangiostrongyliasis globally, One Health (2022). DOI: 10.1016/j.onehlt.2022.100426