Researchers have increased knowledge of the lifecycle of some parasites by studying snails in Thailand. These parasites can cause severe infections in humans who consume raw or improperly cooked fish that have fed on infected snails.

Parasitic flatworms were found to use several species of thiarid snails, commonly found in freshwater environments in Southeast Asia, as their first intermediate host.

“Trematode infections are major public health problems affecting humans in Southeast Asia. Trematode infections depend not only on the habit of people, but also on the presence of first and second intermediate host species, resulting in the endemic spread of parasites, such as intestinal and liver flukes in Thailand,” said scientists.

Snails belong to the genus Stenomelania, have elongated and pointed shells and can be found near and in the brackish water environment of estuaries from India to the Western Pacific islands, including Hawaii.

Studying snails to understand the scale of problem
The study, conducted by Thai and German researchers, was published in the journal Zoosystematics and Evolution.

Researchers collected 1,551 Stenomelania snails between February 2018 and 2019, identified as four species, from streams and rivers near the coastline of the south of Thailand in Krabi, Trang and Satun Provinces. Ten were infected with trematodes. The parasites were found at seven of the 13 studied locations and belonged to three different species. In Krabi Province, the team found all three species.

Scientists suspect their presence could be related to the circulation of sea currents, as the flow of water along the Andaman coast is affected by the monsoon season between January and May and August and October.

Previous research has found at least 70 species of foodborne and waterborne trematodes, such as blood, intestinal, liver and lung flukes, can be found in various animals.

The Food and Agriculture Organization of the United Nations (FAO) produced factsheets in 2020 on foodborne parasitic infections such as paragonimiasis, taeniasis and cysticercosis, cystic and alveolar echinococcosis, clonorchiasis and opisthorchiasis and fish liver flukes.

Researchers said information on the susceptibility of Stenomelania snails to foodborne zoonotic infections provides information on public health in the region.

They added further study of the snails will enhance understanding of the host-parasite relationship as the first intermediate host populations in Thailand. This will also determine the role of parasitic infections in humans and animals in Southeast Asia.