(Credit: Clonorchis sinensis by Marc Perkins/Flickr)

climate change

Will sea level rise boost parasitic flatworms?

To find clues to the future effects of possible climate change, a paleobiologist has turned to ancient mollusk fossils.

John Huntley’s study of clams from the Holocene Epoch, which began 11,700 years ago, indicates that current sea level rise may mimic the same conditions that led to an upsurge in parasitic trematodes, or flatworms, he found from that time.

Huntley cautions that an outbreak in human infections from a related group of parasitic worms could occur and advises that communities use the information to prepare for possible human health risks.

Trematodes are internal parasites that affect mollusks and other invertebrates inhabiting estuarine environments, which are the coastal bodies of brackish water that connect rivers and the open sea.

clam shells
Specimens from the study show “pits” from parasites. (Credit: John Warren Huntley)

Shell ‘wounds’

Huntley, assistant professor of geological sciences at University of Missouri, studied prehistoric clam shells collected from the Pearl River Delta in China for clues about how the clams were affected by changes caused from global warming and the resulting surge in parasites.

“Because they have soft bodies, trematodes do not leave body fossils,” Huntley says.

“However, infected clam shells develop oval-shaped pits where the clam grew around the parasite in order to keep it out; the prevalence of these pits and their makeup provide clues to how the clams adapted to fight trematodes.

“When compared to documented rises in sea level more than 9,300 years ago, we found that we currently are creating conditions for an increase in trematodes in present-day estuarine environments. This could have harmful implications for both animal and human health, including many of the world’s fisheries.”

Foodborne infections

Modern-day trematodes will first infest mollusks like clams and snails, which are eaten by shore birds and mammals including humans.

Symptoms of infection in humans range from liver and gall bladder inflammation to chest pain, fever, and brain inflammation. The infections can be fatal.

At least 56 million people globally suffer from one or more foodborne trematode infections, according to the World Health Organization.

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Huntley and his team compared these findings to those from his previous study on clams found in the Adriatic Sea. Using data that includes highly detailed descriptions of climate change and radiocarbon dating, Huntley noticed a rising prevalence of pits in the clam shells, indicating a higher prevalence of the parasites during times of sea level rise in both the fossils from China and Italy.

“By comparing the results we have from the Adriatic and our new study in China, we’re able to determine that it perhaps might not be a coincidence, but rather a general phenomenon,” Huntley says.

“While predicting the future is a difficult game, we think we can use the correspondence between the parasitic prevalence and past climate change to give us a good road map for the changes we need to make.”

The findings appear in the Proceedings of the National Academy of Sciences.

Partial funding for the study came from the University of Missouri Research Council, the Alexander von Humboldt Stiftung, the German Academic Exchange Service (DAAD), and the National Science Foundation of China.

Source: University of Missouri

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