Preventing the spread of a deadly virus to Pennsylvania's rabbits and hares

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Rabbit hemorrhagic disease virus type 2 is a terrible way for any animal to die, especially creatures as gentle as these. Highly contagious and lethal, it threatens wild and domestic rabbits. First detected in the United States in 2020, it has rapidly spread throughout the western states, becoming endemic as far as South Dakota, Kansas, and Texas. Two years later, Pennsylvania had its first two cases at a Fayette County domestic farmed rabbit facility.

Fortunately, it hasn't happened since. But it could.

For that reason, Penn Vet's Wildlife Futures Program (WFP) has embarked on a genetics study to provide the information needed in the event of future outbreaks.

"This research is intended to help wildlife management agencies develop a plan to be able to respond very quickly," said Sarah Tomke, Ph.D., the postdoctoral researcher hired by the WFP to do the study. "A lot of management is reactive. You have a disease outbreak, and the initial reaction is 'What do we do now?' This research is trying to get ahead of that because this virus spreads so rapidly. Once we have an outbreak in a population, we need to know exactly what to do right now."

Not only is the rabbit hemorrhagic disease virus type (RHDV-2) highly contagious, it has a very high mortality rate. When there has been an outbreak in the wild, the virus has been known to kill up to 70% to 100% of a given rabbit population, according to experts.

RHDV-2 was only first detected in 2010 in France. Since then, it has spread to several other countries.

An infected animal can die quickly, in a day or less. For others, death is more protracted. Symptoms can include bleeding from the nose and mouth, liver failure, convulsions, neurological abnormalities, and heart or respiratory distress. Because the virus hasn't spread to midwestern or eastern states, our rabbits haven't developed any immunity to the virus.

Tomke's study focuses on Eastern cottontails, a very plentiful wild species in Pennsylvania. And since rabbits are very social creatures, she notes, Eastern cottontails are very likely to make contact with domestic rabbits kept outdoors, whether they are pets or commercial animals.

Taking a proactive approach to protect our most vulnerable species

Of particular concern, Tomke said, are the at-risk rabbit species that are fewer in number, particularly those of greatest conservation need.

"Our bigger concern is that this virus will spread into Eastern cottontails and then jump into our more vulnerable species, like snowshoe hares and Appalachian cottontails," Tomke said. "If those become infected, we could see massive die-offs in those species that cannot recover."

Erica Miller, senior research investigator and wildlife veterinarian with the WFP, said RHDV-2 is a particularly scary virus for a number of reasons.

In addition to its threat to both domestic and wild rabbits and its high mortality rate, Miller said RHDV-2 has a very short incubation period, and it is easily spread by insects like fleas and environmental factors.

"A lot of the spread that has happened in domestic animals has actually come from straw and hay that was contaminated out west and then moved here," Miller said, adding there is speculation that this was the origin of the Fayette County infections.

There is no cure for the virus. "But," Miller said, "we do strongly encourage that any domestic rabbits be vaccinated so that we prevent that introduction of the virus into them and possible spill over into the wildlife."

To do her study, Tomke worked with members of the public, including hunters from around the state, to collect two-inch ear clippings from deceased Eastern cottontails.

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Folks were responsive. Tomke received samples from about 1,400 rabbits and was able to genetically sequence 816. "That is a really, really great sample size," she said. "I think we're going to have good results from all of this."

Tomke is still analyzing data and doesn't expect to have final results until sometime this summer. Ultimately the goal is to understand how cottontail populations are distributed across the state by tracking gene flow and to determine how different landscapes—roads, streams, lakes, mountain ranges—affect where and how far they move.

In general, the rabbits have small home ranges, and individual rabbits usually don't travel that far, Tomke said. But since there are so many Eastern cottontails in Pennsylvania, some are bound to cross landscape barriers and connect with other Eastern cottontail populations, she added. That's what seems to be happening.

"It does seem, from preliminary evidence, that Eastern cottontails are very connected across the entire state, so there is a lot of gene flow going on," Tomke said.

More will be known when Tomke is finished with her study and issues her final report. As a geneticist, her expertise isn't advising how to use information. Rather, her study is intended to give wildlife management agencies the information so they can be prepared in case there is another outbreak.

"This research is supposed to help develop a plan to be able to respond very quickly," she said.

Key concepts

disease vectorsvirusesvirology

Provided by University of Pennsylvania