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New virus threatens tilapia industry

Researchers found the culprit behind mass die-offs in Ecuador and Israel in recent years.

An international team of researchers has identified a new virus that attacks wild and farmed tilapia.

In work published this week in mBio, the online open-access journal of the American Society for Microbiology, the team clearly shows that the Tilapia Lake Virus (TiLV) was the culprit behind mass tilapia die-offs that occurred in Ecuador and Israel in recent years. The work also provides a foundation for developing a vaccine to protect fish from TiLV.

In 2009, both wild tilapia species in Kinneret Lake, also known as the Sea of Galilee, and fish in commercial ponds in Israel began suffering from an unknown disease with high rates of mortality of up to 70 percent.

A couple of years later, fish in commercial ponds in Ecuador also suffered a mass die-off. On first glance, the two diseases seemed unrelated because the fish in Israel showed brain and nervous system symptoms while the fish in Ecuador suffered from liver symptoms.

In late 2012, researchers working on both outbreaks sent diseased fish samples to the lab of W. Ian Lipkin, an expert in hunting down new viruses.

The team found 10 short RNA gene sequences. "The more we studied them, the more convinced we became that what we had represented an entirely new virus," said Lipkin.

And because the viruses from the two sites shared almost identical gene sequences, the team believes they came from the same source. But how the virus traveled between Israel and Ecuador, and in which direction, is still a mystery.

"Our research provides the first means of detection -- knowing the genetic sequence of the virus is the first step to designing diagnostic and screening assays," said Eran Bacharach, a molecular virologist at Tel Aviv University. Such tests will allow fish farmers to detect when the virus is present in a commercial pond and limit its spread.

The finding brings other practical applications with it, too, said Lipkin.

"Building a vaccine would save billions of dollars and preserve an industry that ensures employment in the developing world and food security."

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