Unusual virus may tie snakes in knots

By Science News Updated at 2012-08-18 18:09:36 +0000

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A newly discovered class of virus may be at fault in a disease that causes snakes to regurgitate their food, stop eating, and even twist themselves into knots.

Researchers at the University of California, San Francisco, found three new viruses in captive snakes with inclusion body disease, a fatal illness that strikes boa constrictors and pythons and causes clumps of proteins to build up in the snakes’ cells. The unusual genetic makeup of the viruses could give scientists clues to virus evolution stretching back to the age of the dinosaurs.

“It is so different from anything out there it’s almost unrecognizable. It’s way out there,” says Joseph DeRisi, a Howard Hughes Medical Institute investigator at UCSF who led the work, which appears online August 14 in mBio.
The newly identified viruses are similar to arenaviruses, a class previously found only in rodents. Sometimes an arenavirus, such as the one that causes Lassa hemorrhagic fever, will infect a human, but the viruses have never been found in reptiles before.

But the snake viruses have a feature not seen in any arenavirus — a gene found in Ebola, which is in a completely different class called filoviruses. Virologists never thought it possible that those two classes could swap genes, says William Gallaher, a virologist and emeritus professor at Louisiana State University Health Sciences Center in New Orleans.

Ebola could have mixed with arenaviruses long ago, resulting in the combination snake virus. But Gallaher thinks the possibility is slim. The two virus types have different biology, so finding them both active in the same cell at the same time to mix their genetic material seems unlikely, he says.

DeRisi is excited about another possibility: Perhaps the snake viruses are an ancient ancestor to the arenaviruses and filoviruses. “Maybe what you’re looking at is a dinosaur virus eons old,” he says. The ancient reptile viruses may then have given rise to arenaviruses that infect rodents.

Or it could be the other way around: The newly discovered viruses may have originally infected rodents, as arenaviruses do today. Sometime in the murky past, a rodent may have passed its virus on to the snake that ate it, says coauthor Mark Stenglein, a virologist working in DeRisi’s lab. “We call that the rodent revenge hypothesis.”

There is no evidence that modern mice are passing the disease to pet snakes, Stenglein says. And although the viruses were found in snakes with inclusion body disease, that doesn’t necessarily mean the virus causes the illness. The next step will be to infect healthy snakes with the viruses to see if they develop the disease.

The snake viruses are so different that they are probably in a class by themselves, DiRisi says. An international board of experts on viral taxonomy will have the final say over whether the viruses are really a new class, but DeRisi is confident they are distinct. “It’s kind of a no-brainer,” he says.

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