Science

New Vaccine Could Save Rabbits from Fatal Disease


Driving his car through a Tennessee ice storm in early February was a risk that veterinarian Logan Kopp knew he had to take. The reward: rescuing four vials containing 40 doses of a new vaccine for a highly contagious and fatal virus afflicting rabbits. A storm-related power outage had knocked out refrigeration at Priest Lake Veterinary Hospital in Nashville-Antioch, Tenn., threatening to degrade the vaccines doses in cold storage there.

Kopp managed to preserve the vials of vaccine by transferring them from his workplace to his home refrigerator. “It was pretty awful,” he recalls of the treacherous drive, which took nearly six hours to complete in the storm. But he felt he had no other option.

The virus, known as RHDV2, causes rabbit hemorrhagic disease, a form of hepatitis. It is currently spreading through wild and domestic rabbit populations in the U.S., Mexico and beyond. The disease progresses rapidly and is fatal for up to 90 percent of infected rabbits. The virus spreads largely by contact among the animals and their body fluids. Surfaces, such as people’s clothing, can also transmit it.

RHDV2 is not known to infect humans. But human movement of rabbits is likely a significant factor in the disease’s spread, with geographically random cases popping up in domestic rabbits, says Bryan Richards, emerging disease coordinator at the National Wildlife Health Center in Madison, Wis.

Fortunately, as Easter approaches, things are looking up for at least some rabbits. In September 2021 the U.S. Department of Agriculture’s Center for Veterinary Biologics granted emergency authorization for a vaccine against the disease. The following month a vaccine clinic appeared in California, where southern counties had experienced a wild outbreak of the virus. Rabbit owners’ groups shared resources and information online about the resurgent virus and newly available vaccine. By this spring, more than 40 states and Washington, D.C., have access to the vaccine, according to the manufacturer Medgene Labs. A Web site serving rabbit owners lists more than 400 clinics and other sites offering RHDV2 vaccination. Many veterinary practices with vaccine in stock are reaching out to clients who own rabbits and are encouraging vaccination.

When Tennessee’s first cases of rabbit hemorrhagic disease were confirmed in late January, Kopp knew the clock was ticking to protect the area’s rabbits. The vaccine doses he saved during the storm were among the first Priest Lake Veterinary Hospital received.

That clinic has since vaccinated about 170 rabbits, 110 of them at a drive-through vaccination event hosted by the clinic in March. But there are a lot more rabbits out there: about 1.7 million households in the U.S. keep at least one as a pet, according to the American Pet Products Association. In some areas of the country, vaccine appointments are hard to find. One of Kopp’s clients drove nine hours round trip to get her bunny vaccinated.

The virus is now endemic in 11 U.S. states, and cases have popped up in wild or domestic rabbits in 19 states over the past year, according to a frequently updated USDA map.

Estimates of population sizes of the country’s predominant rabbit species—such as domestic rabbits, which are typically kept as pets, eastern cottontails and species of jackrabbits—are difficult to obtain. As many as 3,500 riparian brush rabbits, an endangered species, live at the San Joaquin River National Wildlife Refuge, says Deana Clifford, a senior wildlife veterinarian at the California Department of Fish and Wildlife (CDFW).

Scientists are worried that RHDV2 could threaten the riparian brush rabbit population, along with other rare or endangered species of lagomorphs. A total of 24 rabbit species, or closely related species, worldwide are designated as endangered or vulnerable to extinction by the International Union for Conservation of Nature’s Red List of Threatened Species. Since 2010 RHDV2 has caused outbreaks of rabbit hemorrhagic disease on five continents, according to a 2021 study published in Transboundary and Emerging Diseases.

The long-term impacts of the virus and its vaccine are unclear. Vaccination can save lives of pet rabbits. But trapping and vaccinating sufficient numbers of most wild rabbit species—at least 60 percent of a region’s population—to control an outbreak can be challenging and costly, says Carlos Rouco Zufiaurre, an ecologist at the University of Córdoba in Spain. He explains that the vaccine’s protection eventually wanes, which could enable viral spread to resume in groups of wild rabbits.

Nevertheless, CDFW and other partners have undertaken an effort to vaccinate the riparian brush rabbits at the San Joaquin River refuge. The team procured vaccines made in France, which were available under special conditions before the U.S.-produced vaccine. About 700 rabbits at the refuge have been vaccinated to date, Clifford says. “What we’re trying to do is keep about 15 to 20 percent of the population vaccinated at any given time [so] that, if and when the disease ever comes to the refuge…, we don’t lose them all,” she adds.

Vaccines have also reached the endangered Columbia Basin pygmy rabbit, the smallest species in North America, under a recovery effort led by the Washington Department of Fish and Wildlife and the U.S. Fish and Wildlife Service. Clifford explains that while not all rabbits can be vaccinated, “in these special circumstances, we do think vaccination can have an impact.”

The California outbreak, which also affected rabbits in the Southwest and Mexico, occurred from 2020 to 2021. The episode in those regions combined represents one of the largest recorded North American outbreaks of RHDV2, according to the 2021 Transboundary and Emerging Diseases study. The rapid spread of the virus was a surprise, says Andrea Mikolon, a veterinarian at the California Department of Food and Agriculture and a co-author of the study.

The outbreak first gained CDFW’s attention in May, when biologists in the state found over a dozen dead black-tailed jackrabbits in the desert north of Palm Springs, says Clifford, who is also a co-author on the outbreak study. Into 2021 CDFW typically received citizen reports of one to five dead rabbits at a time, with occasional reports of large numbers of deaths.

No wild cases have been confirmed in California this year, but Clifford says the disease can spread undetected.

For now, the hope is that the campaign among veterinarians to vaccinate pet rabbits could slow the spread of RHDV2 in the U.S. Kopp takes time to speak with many clients, explaining that reliable clinical trials have shown the vaccine to be safe and effective. “There’s definitely some excitement, but I think a lot of people are just nervous just because it’s unknown,” Kopp says. For now, he’ll keep working to protect rabbits, one phone call and one vaccine at a time.


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