A mysterious condition called Inclusion Body Disease (IBD) strikes captive boa constrictors and pythons, causing bizarre behavioral changes and eventually death. Scientists investigating an outbreak of IBD among snakes at the Steinhart Aquarium in San Francisco report they may well have found a virus that is responsible for this common but deadly disease, a discovery that could eventually lead to prevention and treatment options. The study appears in the August 14 issue of mBio®, the online open-access journal of the American Society for Microbiology. The authors report that the virus represents a whole new class of arenaviruses scientists have never seen before.
Among captive boas, IBD is the most commonly diagnosed disease that is thought to be caused by a virus. Snakes that have contracted IBD may initially regurgitate food, but they eventually show dramatic neurological problems, says Michael Buchmeier, a professor of infectious diseases at the University of California, Irvine. Neurological signs include "stargazing," in which the snake stares upwards for long periods of time.
"Some of the symptoms are pretty bizarre -- this stargazing behavior, looking like they're drunk, they tie themselves in a knot and they can't get out of it," says Buchmeier. The condition, which is named for the inclusions, or pockets of foreign material, found inside the cells of affected animals, is ultimately fatal. IBD is devastating for large aquariums, as it can infect a large number of snakes before it is identified and quarantine measures can be put in place. Since there is currently no treatment for the disease, infected snakes must be euthanized to prevent them from infecting other animals.
When the disease recently struck a number of boas and pythons at the Steinhart Aquarium at the California Academy of Sciences, the aquarium requested help from scientists at the University of California San Francisco who specialize in discovering novel viruses.
The researchers extracted DNA from tissue samples taken from boas and pythons diagnosed with IBD, and used rapid, high-throughput techniques to learn the sequence of those strands of DNA. In amongst all the snake DNA sequences there were sequences of DNA that clearly belonged to viruses -- viruses that are members of the arenavirus family. The authors were later able to grow and isolate one of those viruses using snake tissues cultured in the laboratory.
While it is an important development from a practical standpoint, since identifying the causative agent for a disease is the first step in developing treatments, vaccines, diagnostics, and prevention policies it is also an incredible discovery for virology: the virus belongs to a group of viruses no one knew existed.
"This is one of the most exciting things that has happened to us in virology in a very long time. The fact that we have apparently identified a whole new lineage of arenaviruses that may predate the New and Old world is very exciting," says Buchmeier.
According to Buchmeier, this new isolate doesn't fall neatly into either of the two known categories of arenaviruses, Old World arenaviruses and New World arenaviruses. The fact that the virus was found in snakes adds another surprise twist, since up until now arenaviruses had only ever been found in mammals.
Metagenomic techniques that examine large samples of DNA for small bits of information, like the approach used in the study, are extremely powerful for identifying new viruses, Buchmeier says.
"Twenty years ago we would have called this a fishing expedition. It is fishing, but the techniques are so good and so sensitive that they allow us to determine which new types are there," says Buchmeier.
- Mark D. Stenglein, Chris Sanders, Amy L. Kistler, J. Graham Ruby, Jessica Y. Franco, Drury R. Reavill, Freeland Dunker, and Joseph L. DeRisi. Identification, Characterization, and In Vitro Culture of Highly Divergent Arenaviruses from Boa Constrictors and Annulated Tree Boas: Candidate Etiological Agents for Snake Inclusion Body Disease. mBio, July/August 2012 DOI: 10.1128/mBio.00180-12
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