Natures wonders: lungworm lifecycle hosts (Introduction)

by David Turell , Friday, August 26, 2022, 17:36 (608 days ago) @ David Turell

A problem in Hawaii andv tropics:

https://phys.org/news/2022-08-slugs-snails-rat-lungworm-disease.html

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

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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 in which the worms reach maturity 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, and this can lead to serious illness and occasionally death.

"But people can also get infected if they eat so-called paratenic hosts, which are also known as carrier hosts," said Cowie, who is a research professor in the Pacific Biosciences Research Center at SOEST. "These are animals that become infected by eating infected snails or slugs, but in which the worms cannot develop to maturity as they do in a rat. However, in such hosts the worms become dormant, but still infective. And if one of these hosts, or part of one, is then eaten raw by a person—an accidental host—development can continue, but only up to a point."

That point is when they are in the person's brain, where they are moving around, feeding, and growing. But then the worms die. The damage to the brain and the massive inflammation that results when they die is primarily what causes the symptoms of rat lungworm disease.

"Rat lungworm disease is at present confined largely to the tropics and subtropics, notably parts of South and Southeast Asia, where it probably originated, southern China, Taiwan, southern Japan, various Pacific islands and archipelagos, and more recently Brazil, Caribbean islands, and Australia. The parasite has also been reported from the Canary Islands and Balearic Islands of Spain, as well as southeastern parts of the United States, where there have been a handful of cases of rat lungworm disease. Climate change may lead to its further spread into currently more temperate regions.

"Hawai'i is a global center of the incidence of rat lungworm disease, and indeed it was in Hawai'i where the connection between the parasite and the disease was first discovered, by University of Hawai'i and US government scientists in the early 1960s.

"'Several species capable of acting as carriers (paratenic hosts) are present in Hawai'i, including flatworms, centipedes, coqui frogs, and cane toads," said Cowie. "While people in Hawai'i are unlikely to eat these animals, it is not unknown for people to do so on a dare, and become seriously ill. Elsewhere, certain paratenic hosts are eaten for supposed health reasons—frogs in Taiwan and Japan, or to enhance virility—lizards in Thailand."

"Domestic animals, especially dogs and horses, can also become infected by the rat lungworm parasite, including in Hawai'i, probably mostly from accidentally or deliberately eating snails or slugs."

Comment: to forestall dhw's usual comment about why God produced these dangerous animals, note they get in trouble with humans if they get into the wrong animals. In their own ecosystem they are just fine.