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New eDNA technique may reduce pathogens in aquatic animal trade

Salamanders and other amphibians can carry harmful zoonotic pathogens. Photo by Kai Wang/WSU
Salamanders and other amphibians can carry harmful zoonotic pathogens. Photo by Kai Wang/WSU

June 24 (UPI) -- A Washington State University researcher has developed new ways to detect the genetic signatures of disease in the international aquatic animal trade.

The methods call for the screening of environmental DNA, or eDNA -- genetic material collected from the environment -- not an animal's cells, according to a study published Wednesday in the journal Scientific Reports.

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Bats and livestock aren't the only animals carrying potentially harmful diseases -- fish and amphibians can also carry zoonotic pathogens.

With aquaculture now the fastest growing sector of animal protein production, the international trade of aquatic animals could pose a growing threat to human health. Diseases transported through the international pet trade can also threaten native fish and amphibian populations.

Every year, 225 million live animals are imported into the United States. Screening all of these animals individually would be cost and labor prohibitive, researchers say.

To tackle the problem, researcher Jesse Brunner, a professor of disease ecology at Washington State, developed a pair of more efficient screening methods.

According to Brunner, test samples could be batched before analysis. Scientists could also survey water samples from animal tanks for the presence of dangerous pathogens.

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"The best way to prevent the emergence of these pathogens, and the diseases that come from them, is to keep them from getting here in the first place," Brunner said in a news release. "It's an important goal but a really hard one because of the scale of the problem. With the eDNA method, you are theoretically sampling an entire population at once, so you are more likely to detect whatever is there, and you can do that much more efficiently than with traditional approaches."

Like humans, animals infected with pathogens shed pieces of the virus or invading bacteria. These DNA fragments will end up in the water in which they're living.

Batrachochochytrium salamandrivorans, or Bsal, is one of the pathogens that scientists could use eDNA screening methods to detect, researchers say.

The fungus is a major threat to amphibian species. It was recently introduced to native salamander populations in Europe by pets imported from Southeast Asia. In 2016, the U.S. Fish and Wildlife Service banned the importation of 201 species of salamanders into the United States.

In her paper, Brunner used statistical formulas to determine the volume of samples that would need to be analyzed in order to be confident that imported animals were free of harmful pathogens.

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Researchers are currently using real samples to test the efficacy and efficiency of Brunner's screening methods.

"The problem that we're having with amphibians is also the same problem that we're having with all sorts of wildlife and with human disease," said Brunner. "I think if we can solve this problem, we'll be in much better shape to solve others."

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