Model for the recombination and transfer of Equine herpesvirus 1, a zebra-derived virus, to polar bears. Credit: IZW / Zoo Wuppertal
In Wuppertal Zoo in 2010 sad sadness prevailed: The polar bear female Jerka had died of a mysterious encephalitis, and her male conspecific Lars had narrowly escaped this fate. For a long time the zoo vets puzzled what might have caused the disease. Now, an international research team has demonstrated that the bears were infected with a recombinant zebra-derived virus that apparently could skip the species line between these two so different animals. Zoos house many different species of animals that would never meet in the wild. That this could lead to unforeseen transmissions of pathogens, was not necessarily considered a danger .. Because normally pathogens are adapted to a particular host, only a few can overcome species boundaries. In close relatives, such as mouse and rat or human and apes, this is still comparatively common. However, the current study shows that some viruses can evidently also develop enormous bounce and infect animals that separate millions of years of evolution.

"When we started the investigations, there was an almost endless list of pathogens that could have caused Jerka's death, " reports study leader Alex Greenwood of the Berlin Leibniz Institute for Zoo and Wildlife Research. However, by extensive research by Jerka, Lars and nine other polar bears, the researchers could finally identify a herpes virus as a cause. It was, however, a form that was previously known only from infections in zebras.

Analysis of the genetic sequence of the virus revealed that the pathogen is a combination of the genome of two different viruses that infect both zebras. Although recombination is not uncommon in herpesviruses, it appears that a genetic combination has been developed in this case that is already known to be the cause of neurological diseases, especially in horses. Whether the virus has evolved recently in zoos in the zoo or long ago in Africa, and whether the recombination event is responsible for the intermediate bounce remains unclear.

It is also unknown how the polar bears got infected. Polar bears and zebras are cared for by various animal keepers in the Wuppertal Zoo, and their enclosures are located about 70 meters apart. One possibility that the authors of the study are currently exploring is the transmission of viruses by free-living infected mice or rats. "These viruses may be able to overcome many species barriers? In fact, we do not even know if they even have species borders, says Klaus Osterrieder from the Free University of Berlin. In some species, the infection may be without disease symptoms. In the Zoo Wuppertal one is now at least warned: "We will regularly test our animals for the virus. Now that we know more about it, we are better prepared and can be active in advance, "says Arne Lawrenz from Zoo Wuppertal. display

Alex Greenwood (Berlin Leibniz Institute for Zoo and Wildlife Research) et al .: Current Biology, doi: 10.1016 / j.cub.2012.07.035 © science.de? Martin Vieweg

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