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October 01, 2020

Rabbits across US likely vulnerable to deadly virus causing disease in the West

Rabbit hemorrhagic disease virus serotype 2 affecting cottontails, jackrabbits
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A virus killing rabbits in the Southwest and West could spread among vulnerable species across North America.

Rabbits and hares across the continent may be susceptible to rabbit hemorrhagic disease virus serotype 2, which caused sporadic outbreaks in domestic rabbits in North America before it was first discovered in wildlife this March in New Mexico.

Eastern cottontail rabbit
Eastern cottontail rabbits, abundant throughout much of North America, are among the species susceptible to rabbit hemorrhagic disease virus serotype 2. (Courtesy of U.S. Fish and Wildlife Service.)

It since has spread to Arizona, California, Colorado, Nevada, Texas, and Utah and is killing domestic rabbit herds and at least four wild lagomorph species. Mexico is dealing with concurrent outbreaks in its northern states.

Dr. Julianna Lenoch, a veterinary epidemiologist for the U.S. Department of Agriculture, said Aug. 14 the U.S., fortunately, saw little recent spread of the virus.

“We haven’t had a new state or expansion reported in the last 60 days,” she said. “But most of the rabbit groups and wildlife partners are on high alert for any further disease incursion.”

The deaths reported so far among domestic and wild rabbits suggest the virus has a mortality rate somewhere between 50% and 90%, Dr. Lenoch said.

As of mid-August, the virus had spread in the wild among desert and mountain cottontails and black-tailed and antelope jackrabbits, she added. Researchers with the USDA’s Animal and Plant Health Inspection Service’s  Foreign Animal Disease Diagnostic Laboratory have shown that eastern cottontails also are susceptible to the virus.

The U.S. habitat for eastern cottontails stretches from the Great Plains to the East Coast, overlapping with the native ranges of desert and mountain cottontails in the west and New England cottontails in the east, according to information from the U.S. Fish and Wildlife Service and U.S. Geological Survey.

Pikas may also be among the susceptible species, and the same is true for threatened and endangered rabbit species, Dr. Lenoch said. APHIS is working with state agencies to protect those animals, she said.

The riparian brush hare, for example, survives in a limited span of northern California. The Columbia Basin pygmy rabbit lives in five counties of Washington state.

Since February 2018, RHDV2 has caused illnesses among feral rabbits on Vancouver Island in British Columbia, a pet rabbit in Ohio, island-bound pet and feral European rabbits in Washington state, and pet rabbits linked with a veterinary clinic in New York City, according to an APHIS emerging risk notice published this July.

“I don’t know that we expect any type of geographic containment due to where we’ve already seen detections,” Dr. Lenoch said.

In a July 13 article from Tufts University, Dr. Jennifer Graham, head of the Cummings School of Veterinary Medicine zoological companion animal medicine service, said that, once the virus gets into a wild rabbit population, there’s no way to stop it from rapidly spreading and becoming endemic.

“Veterinary epidemiologists feel this disease is going to be pretty established throughout the country by next year,” she said.

Hardy and highly deadly

Dr. Julia Lankton, a wildlife pathologist for the USGS National Wildlife Health Center, said the virus is highly contagious, with potential to infect rabbits and hares through oral, nasal, conjunctival, or parenteral routes.

It spreads through contact with infected animals and their secretions or excretions, which can be on contaminated bedding or forage. It also can spread by vectors such as flies, carnivores, and scavengers, as well as fomites such as clothing, shoes, and farm or home tools.

Dr. Lenoch said RHDV2 is persistent in wild environments, lasting three months or more in organic material and remaining viable despite freezing or high temperatures. The virus is hardy enough that she doesn’t expect large seasonal fluctuations in infections.

Dr. Lankton said the virus attacks a rabbit’s liver first. The damage may cause disseminated intravascular coagulation, a condition in which blood clots block small blood vessels and deplete platelets and clotting factors, reducing the body’s ability to produce clots where needed. This leads to multiorgan hemorrhage and death.

Bryan Richards, emerging disease coordinator for the USGS National Wildlife Health Center, said humans almost definitely helped the virus jump long distances, including its leap across the Atlantic from Europe to Quebec in 2016 and its emergence in British Columbia. Since it reached the Southwestern U.S., multiple mechanisms have likely contributed to its spread among wild and domestic rabbits.

Dr. Lenoch said animal health investigators have been unable to determine how the virus arrived in the Southwest. Genetic sequences from wild and domestic rabbits showed the strains were clonal and so offered no clues on its introduction.

The virus already established a substantial geographic footprint even though rabbits and hares are nonmigratory and tend to spend their lives in small areas, Richards said. Whether that footprint expands will depend, in part, on whether contiguous populations support continued rabbit-to-rabbit spread.

The outbreak in New York City involved 11 pet rabbits, linked by a veterinary clinic. Dr. Lenoch called owners of exposed animals.

“And 155 interviews later, none of them reported ever seeing wild rabbits in the neighborhood,” she said.

In the Southwest, people often raise rabbits in backyard hutches or enclosures, where domestic rabbits can have close encounters with wild ones.

Dr. Lenoch said the USDA lacks regulatory authority to implement quarantines or movement controls over rabbits. APHIS is relying on state agriculture and wildlife departments and giving them help to improve disease controls and mitigation efforts.

High alert amid rapid spread

Dr. Lankton noted that RHDV2 spread rapidly across Europe and Australia after its introduction and discovery in each. She cited a January 2018 scientific article, published in the Journal of Virology, that indicates the virus spread 3,500 kilometers coast to coast across Australia within 18 months of its detection in May 2015.

People who work with rabbits—domestic or wild—are on high alert, Dr. Lenoch said. Those stakeholders include farmers who raise rabbits for meat, fur, or medical applications, as well as breeders and rescue organizations.

APHIS is working on outreach and giving guidance on biosecurity, cleaning, disinfection, and how to avoid bringing the virus into a rabbit farm. And Dr. Lenoch noted that the U.S. Environmental Protection Agency provides a list of disinfectants suitable for use against RHDV2.

State animal health officials and state veterinarians are the best sources of information for rabbit owners, she said.

Earlier this year, USDA officials authorized emergency use of two European vaccines against the RHDV2 virus in states with confirmed RHDV2 infections. Veterinarians who gain approval from their state veterinarians can apply for permits from the APHIS Center for Veterinary Biologics to import the killed-virus vaccines.

Richards also has some positive news: Every mortality event in wild populations that he knows of, large or small, had some survivors in the same area. It’s unclear how many of those rabbits became exposed to the virus and survived infection, he said.

Richards said rabbits, fortunately, rebuild populations quite quickly. But state and federal officials are monitoring for population-level effects on lagomorphs, as well as the potential cascading effects on their predators and environments.

 

The AVMA has information on rabbit hemorrhagic disease virus serotype 2 clinical signs, transmission, prevention, and reporting.