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Wup­per­tal Zoo polar bear killed by zebra her­pesvirus — viruses jump­ing species

pub­lished 24 March 2013 | mod­i­fied 07 March 2014

Zebra-polarbear virusZoos bring together dif­fer­ent ani­mal species that would never encounter each other in the wild. On occa­sion, this can have unfore­seen con­se­quences. When in 2010 at the Wup­per­tal Zoo one polar bear died and another fell severely ill, zoo vet­eri­nar­i­ans were at a loss as to the cause of the symp­toms. It has now been shown that the bears were infected with a recom­bi­nant zebra-​derived virus that had jumped into other species, as reported today by an inter­na­tional team of researchers led by the Leib­niz Insti­tute for Zoo and Wildlife Research in the jour­nal Cur­rent Biol­ogy. Such species-​jumping viruses, if not detected, may threaten the con­ser­va­tion mis­sion of zoos.

Keep­ing ani­mals from around the world is an impor­tant com­po­nent of the mis­sion of zoos to edu­cate the pub­lic and pre­serve endan­gered species. To date, it has rarely been con­sid­ered that such a species mix may have unpre­dictable con­se­quences in terms of trans­fer of pathogens among zoo ani­mals. Gen­er­ally, pathogens adapt to a spe­cific host, but some are oppor­tunis­tic and can spread to new hosts upon encounter.

The study by researchers from the Leib­niz Insti­tute for Zoo and Wildlife Research Berlin (IZW), the Freie Uni­ver­sität Berlin, the Uni­ver­sity of Syd­ney and the Zoo­log­i­cal Gar­dens Wup­per­tal reports such a case of a virus jump­ing from one species to another. The find­ings have been pub­lished on 16 August 2012 in the jour­nal Cur­rent Biol­ogy.

In 2010 at the Wup­per­tal Zoo in Ger­many, a female polar bear, Jerka, died of encephali­tis despite the best efforts of the zoo vet­eri­nar­i­ans to save her. Her male com­pan­ion Lars exhib­ited sim­i­lar symp­toms but sur­vived as a result of inter­ven­tion and long-​term vet­eri­nary care. Dr. Arne Lawrenz, zoo vet­eri­nar­ian in Wup­per­tal, describes the sit­u­a­tion: “The symp­toms were quite shock­ing, and it was com­pletely unclear at the time what was caus­ing them. We tried to sta­bilise both ani­mals for days. In the case of Jerka, we were sadly unsuc­cess­ful. For­tu­nately, how­ever, Lars recov­ered after sev­eral weeks and is still alive today.”

These viruses do not seem to respect species bound­aries and in fact, we don’t really know whether they have any. One conun­drum is that these viruses are not par­tic­u­larly sta­ble in the envi­ron­ment, so it is impor­tant to fig­ure out how they move between species
Prof. Klaus Oster­rieder, Freie Uni­ver­sität Berlin »

Encephali­tis can be caused by a large num­ber of viruses and bac­te­ria, and iden­ti­fy­ing novel pathogens in wild ani­mals is a huge, often insur­mount­able, chal­lenge. How­ever, the inten­sive inves­ti­ga­tion of Jerka, Lars and nine addi­tional polar bears yielded a zebra-​derived her­pes virus as the only can­di­date pathogen. A sur­pris­ing find was that polar bear Struppo, which died years ear­lier from renal fail­ure in a dif­fer­ent zoo with no con­tact to Jerka or Lars, was also pos­i­tive for the virus. This indi­cates that this virus has jumped inde­pen­dently before and may con­tinue to do so.

Inter­est­ingly, the virus turned out to be a recom­bi­nant, i.e. a com­bi­na­tion of the genetic mate­r­ial of two dif­fer­ent viruses both found in zebras. It orig­i­nated when the Equine her­pesvirus EHV9 trans­ferred a por­tion of its DNA into the related EHV1. While recom­bi­na­tion is not uncom­mon for her­pesviruses, the gene region trans­ferred in this case is notable for its role in caus­ing neu­ro­log­i­cal dis­eases even in horses. Whether this novel virus emerged recently in the zoo zebra pop­u­la­tion or a long time ago in Africa, and whether the recom­bi­na­tion event is respon­si­ble for the abil­ity of the virus to jump to new hosts and cause deadly dis­ease are open ques­tions.

“When we started, there was an over­whelm­ing num­ber of poten­tial pathogens that might have caused Jerka’s death”, illus­trates Prof. Alex Green­wood of the IZW, lead author of the study. “At first it seemed easy, because we quickly got a sig­nal for EHV. But when we looked at the viral DNA sequence, it could have been either EHV1 or EHV9. With more sequence data it became clear that there was one gene that was partly like one virus and partly like the other.”

Another open ques­tion is how the bears were infected. Polar bears in Wup­per­tal are not cared for by the same zookeep­ers as zebras. In addi­tion, the zebras are housed 68 meters away, thus direct con­tact is unlikely to be the route of trans­mis­sion. How­ever, bears and zebras are not the only hosts, as the par­ent viruses were asso­ci­ated with fatal encephali­tis in other zoo species such as gazelles and guinea pigs. Prof. Klaus Oster­rieder from the Freie Uni­ver­sität Berlin explains: “These viruses do not seem to respect species bound­aries and in fact, we don’t really know whether they have any. One conun­drum is that these viruses are not par­tic­u­larly sta­ble in the envi­ron­ment, so it is impor­tant to fig­ure out how they move between species.” The authors of the study are cur­rently explor­ing the pos­si­bil­ity that trans­mis­sion could even occur through wild mice or rats.

Being alert to the pos­si­bil­ity of pathogen species jumps and their poten­tially fatal con­se­quences, zoos can serve as sen­tinels for dis­ease out­breaks and pro­tect their ani­mals. How­ever, this impor­tant task will be com­plex, as pathogens may cause no symp­toms in some species or indi­vid­u­als and unex­plained mor­tal­ity in oth­ers. For most of the many pathogens that can cause encephali­tis or fatal­ity, not much is known about their abil­ity to enter new host species. Fur­ther wildlife dis­ease research, bet­ter com­mu­ni­ca­tion between insti­tu­tions and care­ful mon­i­tor­ing will be required to ensure the suc­cess of the con­ser­va­tion mis­sion of zoos. At least one case has been suc­cess­fully resolved though, says Dr. Arne Lawrenz of Wup­per­tal Zoo: “With our col­leagues we have screened our polar bears in Wup­per­tal to make sure they are EHV-​free, and we will do so on a reg­u­lar basis. Now that we are aware of this issue, we are bet­ter pre­pared and can be proac­tive.”

(Source: IZW press release, 16.08.2012)

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