Shots - Health Blog
10:32 pm
Mon August 13, 2012

How A Virus In Snakes Could Offer Clues To Ebola In Humans

Originally published on Tue August 14, 2012 8:55 am

Scientists have found a surprising link between deadly Ebola virus and a disease that's been killing boa constrictors in zoos and aquariums.

A team at the University of California, San Francisco, has found evidence that a previously undiscovered virus is responsible for something called inclusion body disease in boas. And this virus, described in the journal mBio, appears to be related to both Ebola and another deadly class of viruses called arenaviruses.

The discovery should make it possible to contain outbreaks by testing snakes for inclusion body disease before putting them in a collection. It also may help researchers figure out how some dangerous viruses in animals end up infecting people.

"We know a lot about viruses in pigs and bats and mice," says Joseph DeRisi, a virologist at UCSF. "No one suspected snakes might be a repository of information about these hemorrhagic viruses."

DeRisi and his team might never have discovered the virus that's killing snakes without the efforts of a woman named Taryn Hook.

Hook, who lives in the San Francisco Bay Area, had become worried about her snake, a 7-foot-long boa constrictor named Larry.

"Larry is a member of the family in every respect," she says. "He gets in bed with us and watches television. He likes American Idol."

He is also a therapy animal for Hook, who says she suffers from anxiety and obsessive-compulsive disorder. But Larry had been sick for months, Hook says. And veterinarians couldn't figure out why, though they suspected a virus.

Hook was desperate. Then she heard about DeRisi at UCSF. DeRisi became famous in animal circles several years ago when he helped identify a virus killing parrots and other exotic birds.

Hook thought maybe he could save her snake.

"So I wrote him a letter with a picture of myself and Larry in our backyard," she says. "And I pled with him, explaining that he was my last hope."

Hook's letter wasn't just about Larry, but about lots of sick boa constrictors, DeRisi says. It described how inclusion body disease, which Hook suspected Larry might have, had become a major problem in aquariums and zoos, and for people who keep snakes as pets.

The first symptoms of the disease are often that a snake stops eating or begins regurgitating its meals. But eventually, it attacks the snake's brain and nervous system.

"Some of these snakes tie themselves into knots," DeRisi says. "They roll on their back, and they exhibit behaviors like stargazing, where they wave their heads in the sky sort of uncontrollably."

DeRisi thought he might be able to find the cause of inclusion body disease if he looked at genetic material from snakes that had died of it. So he asked around. And he learned that an outbreak had just been discovered in boas at an aquarium a few minutes from his lab.

DeRisi's lab extracted lots of genetic material from the sick boas. And DeRisi was pretty sure that somewhere in all that genetic material was code for the virus causing inclusion body disease.

The trick was to figure out which genetic material belonged to the snakes and which belonged to the virus. A researcher in DeRisi's lab named Mark Stenglein did that by comparing all the genes found in the sick boas with the complete genetic code, or genome, of a healthy red-tailed boa named Balthazar.

"With the boa genome in hand, Stenglein could filter away what was boa, leaving behind what was not boa, presumably the thing making them sick," DeRisi says.

The approach worked. Stenglein soon found genetic code for a virus related to so-called arenaviruses, which can cause deadly infections in people. "But they were different from all previously described arenaviruses," Stenglein says

No one had ever found an arenavirus in a reptile before, so that was pretty big news in itself. But then Stenglein found something even more surprising about this particular arenavirus.

"One of its genes is actually most closely related to the same gene in Ebola virus," he says. "So this virus is actually a mashup, or a genetic mix of arenaviruses and Ebola virus."

The virus kills snakes but appears harmless to people, DeRisi says.

The finding raises two possibilities, DeRisi says. One is that at some point snakes carried both arenaviruses and Ebola viruses, allowing them to swap genes. Another possibility, he says, is that "Ebola and arenavirus as we know them today evolved from this."

Either way, the finding suggests that reptiles can harbor versions of some of the world's most deadly viruses. That information means scientists need to expand the range of animals they study when trying to explain outbreaks of these viruses in people.

As for Larry, the sick boa that started this line of research, tests have shown that he's not infected with the newly discovered virus.

Larry still gets sick from time to time, but his symptoms are being controlled with medication, Hook says.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

DAVID GREEN, HOST:

Scientists have found a surprising link between the deadly Ebola virus and a strange disease that's killing boa constrictors. NPR's Jon Hamilton reports that this finding could help snakes and people.

JON HAMILTON, BYLINE: The discovery might never have been made without the efforts of a woman named Taryn Hook. Hook says she had become very worried about her snake, a seven-foot-long boa constrictor named Larry.

TARYN HOOK: Larry is a member of the family in every respect. He gets in bed with us and watches television. He likes "American Idol."

HAMILTON: And reality TV. But Larry had been sick for months, and veterinarians couldn't figure out why, though they suspected a virus. Hook was desperate. Then she heard about a scientist named Joseph DeRisi at the University of California San Francisco. Several years ago, DeRisi helped identify a virus killing parrots and other exotic birds. Hook thought maybe he could save her snake.

HOOK: So I wrote him a letter with a picture of myself and Larry in our backyard, and I pled with him, explaining that he was my last hope.

HAMILTON: DeRisi says Hook's letter wasn't just about Larry, but about lots of sick boas.

JOSEPH DERISI: It said there is a disease that is present in the boa constrictor community that's killing boa constrictors, and it's a problem in aquariums and zoos, and for domestic owners like myself. My boa's very important to me and I wish you'd look into it.

HAMILTON: So he did. DeRisi learned that something called inclusion body disease had been killing boa constrictors in captivity for decades. He says the disease eventually attacks the snake's brain and nervous system.

DERISI: Some of these snakes tie themselves into knots. They roll on their back, which snakes never roll on their back, and they exhibit behaviors like stargazing, where they wave their heads in the sky sort of uncontrollably.

HAMILTON: DeRisi thought he might be able to find the cause of inclusion body disease if he could look at genetic material from snakes that died of it. So he asked around. And he learned that an outbreak had just been discovered at an aquarium a few minutes from his lab.

DERISI: And when that happens, they take no chances. They euthanize all the snakes. Because it's infectious, they know it can be transmitted, and they know if they don't do something about it, they're going to lose them all.

HAMILTON: Now DeRisi's had lots of genetic material from sick boas. And he thought that somewhere in all that genetic material was code for the virus causing the disease. But he says there was a problem.

DERISI: How do you know what's snake and what's virus?

HAMILTON: DeRisi says the solution was to have the researcher, named Mark Stenglein, compare all the genes found in the sick boas with the complete genetic code, or genome, of a healthy red-tailed boa named Balthazar.

DERISI: With the boa genome in hand, Mark could filter away what was boa, leaving behind what was not boa, presumably the thing making them sick.

HAMILTON: Stenglein says he started looking for genetic code from a virus.

MARK STENGLEIN: And I immediately found something that was potentially very interesting, which was the presence of a large number of sequences that were related to a type of virus called arenavirus, but they were different from all previously described arenaviruses.

HAMILTON: Arenaviruses usually infect rodents, but when they infect humans they can cause deadly outbreaks. No one had ever found an arena virus in a reptile before, so that was pretty big news in itself. But then Stenglein found something even more surprising about this particular arenavirus.

STENGLEIN: One of its genes is actually most closely related to the same gene in Ebola virus. So this virus is actually a mash-up, or a genetic mix of arenaviruses and Ebola virus.

HAMILTON: A mashup that kills snakes but appears harmless to people. DeRisi says the finding, published in the journal mBio, raises two possibilities. One is that at some point snakes carried both arenaviruses and Ebola viruses, allowing them to swap genes.

DERISI: Or this is actually the ancestor of both of those viruses and that Ebola and arenavirus as we know them today evolved from this.

HAMILTON: Either way, the finding suggests that reptiles can harbor versions of viruses that cause deadly outbreaks in people. That information may help researchers prevent future outbreaks, and identifying the new snake virus will mean that aquariums can test an animal for infection before placing it in a collection. As for Larry, the sick boa that started this line of research, tests show he doesn't have the newly discovered virus, and with a little medication, he's doing okay. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.