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Research finds rat lungworm is transmitted to humans by at least 13 species

By on August 29, 2022 0

Puerto Rican shell frog, introduced to Hawaiʻi, where it may be a carrier host for the rat lungworm parasite. Photo courtesy: United States Department of Agriculture

According to researchers from the University of Hawaii at Mānoa and the University of London in the UK, rat lungworm disease can be transmitted to humans by at least 13 species of shrimp, crabs, flatfish , frogs, toads, lizards and centipedes.

Researchers combed through nearly 140 scientific studies published between 1962 and 2022 and found that 32 species of freshwater prawns/prawns, crayfish, crabs, flatworms, fish, sea snakes , frogs, toads, lizards, centipedes, cattle, pigs and snails can act as carriers of the rat lungworm (Angiostrongylus cantonensis) parasite. Of these, at least 13 species have been associated with rat lungworm disease in humans.

Previously, it was well known that the disease was spread by slugs and snails.

Robert Cowie, study lead author and UH Mānoa faculty member School of Ocean and Earth Science and Technology, said it was important to know which other animals could also transmit the disease to humans.

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“The aim of the study was to extract all the information on paratenics [carrier] hosts and their role in transmission of rat lungworm disease, previously scattered in various obscure publications and reports, brought together in one place and developing a comprehensive understanding of their diversity and role in disease transmission,” Cowie said.

Rat lungworm disease is currently largely confined to tropical and subtropical regions, with Hawaiʻi being a world center for it. Hawaiʻi is where the link between the parasite and the disease was first discovered in the early 1960s by UH and US government scientists.

For this research, Cowie supervised Helena Turck, first author and graduate student at the University of London who carried out this study remotely during the pandemic as part of her master’s thesis research. Professor Mark Fox of the Royal Veterinary College also collaborated on the study.

Cowie explained that the rat lungworm has a complex life cycle that involves slugs and snails as so-called “intermediate” hosts and rats as the “definitive” hosts in which the worms mature. and reproduce. Rats become infected when they eat an infected snail or slug. People also become infected when they eat an infected snail or slug, which can lead to severe illness and sometimes death.

Platydemus manokwari, an introduced flatworm present in Hawaiʻi, may act as a carrier host for the rat lungworm parasite. Photo credit: Shinji Sugiura
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“But people can also get infected if they eat so-called paratenic hosts,” Cowie said. “These are animals that become infected by eating infected snails or slugs, but in which the worms cannot grow to maturity as they do in a rat. However, in these hosts, the worms become dormant, but remain infectious. And if one of those hosts, or part of it, is then eaten raw by a person – an accidental host – development can continue, but only up to a point.

The development of rat lungworms occurs when they are in the brain of the person, where they move, feed and grow, but then the worms die without completing their life cycle. Brain damage and the massive inflammation that results when they die are the primary cause of rat lungworm disease symptoms.

“Several species capable of acting as carriers (paratenic hosts) occur in Hawaiʻi, including flatworms, centipedes, coqui frogs, and cane toads,” Cowie said. “Although it is unlikely that people in Hawaii will eat these animals, it is not uncommon for people to do so out of defiance and become seriously ill. Elsewhere, some paratenic hosts are eaten for supposed health reasons – frogs in Taiwan and Japan, or to improve virility – lizards in Thailand.

Domestic animals, especially dogs and horses, can also become infected with the rat lungworm parasite, including in Hawaii, likely primarily by accidentally or deliberately eating snails or slugs.

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Other notable regions where rat lungworm disease is prevalent include South and Southeast Asia, where it likely originated, southern China, Taiwan, southern Japan, various islands and archipelagos of the Pacific, Brazil, the Caribbean islands and Australia. The parasite has also been reported from the Canary Islands and the Balearic Islands of Spain, as well as the southeastern United States. Climate change could lead to its spread to currently more temperate regions.

There are several things people can do to prevent rat lungworm infection.

“Knowing which species may harbor the parasite is critically important both in Hawaiʻi and more broadly,” Cowie said. “These animals should not be eaten raw. Also, wash all fruits and vegetables well under running water and inspect them for slugs, snails, and possible other hosts such as tapeworms to avoid inadvertently eating them or parts of them. ‘between them.

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