Thousands of wild and domestic rabbits across the southwest United States have died of a viral infection.
California’s Department of Fish and Wildlife reported new cases from Palm Springs on May 13, making it the sixth state hit by the virus, rabbit hemorrhagic disease virus type 2, since it was first identified in wild American rabbits in March, Karin Brulliard reports for the Washington Post. The virus causes rabbits and their close relatives—like hares and the mountain-dwelling pika—to drop dead, sometimes with signs of blood near their noses and mouths.
The virus can’t infect humans. But experts worry that threatened species are at risk, and that a disease that hurts wild rabbit populations could have ripple effects up the food chain.
“The outlook right now is so unbelievably bleak,” University of Oklahoma mammologist Hayley Lanier tells Erik Stokstad at Science magazine. “We’re simply left to watch the wave spread out and worry about imperiled species in its path.”
By mid-May, the virus had affected wild rabbits in New Mexico, where it was first found, and then Texas, Arizona, Colorado, Nevada and California. Wild rabbits in Mexico have also caught the bug.
A few cases of the hemorrhagic disease had been seen in domestic rabbits in the U.S. since 2018, but now that it’s in the wild, it is spreading uncontrolled. The virus is sturdy and highly infectious, according to the National Wildlife Health Center. The virus can survive freezing temperatures and nearly four months of dry conditions. It spreads between rabbits not only through contact with a sick bunny, but also by contact with their pelt, meat, or even insects that picked it up from them.
Jesús Fernández, a mammologist at the Autonomous University of Chihuahua, tells Science that he and his colleagues are advising local cattle ranchers to stay on the lookout for dead rabbits with bloody faces. Any corpses they find, they should burn and then bury three feet deep, Fernández says.
It’s not clear how the virus reached wild North American rabbits, but New Mexico state veterinarian Ralph Zimmerman tells the New York Times’ James Gorman that one possibility is the importation of domestic rabbits from Europe. In 2010, the virus was identified in France, and since then it has spread across Europe and later appeared in Australia. The original strain of the virus, type 1, was first identified in China in 1984.
“We hear rumors of underground rabbit transport, and there are folks that do import rabbits from Europe,” Zimmerman tells the New York Times. “So our concern is that somebody brought them in, they were carrying the virus during transport. If one of them died, they pitched it out and boom, we infect the wild rabbits and away we go.”
In addition to the wild rabbits, Zimmerman tells the Washington Post that 470 domestic rabbits in New Mexico died of the virus, and nearly 600 were euthanized at sites that raise rabbits as pets or livestock, while 30 sites are now under quarantine.
European veterinarians offer a vaccine against the hemorrhagic disease, but because the virus was rare in the U.S., it is not yet widely available. States that have seen rabbit deaths due to the hemorrhagic disease can coordinate with the U.S. Department of Agriculture to import the vaccine, as New Mexico has done, to protect some of the 6.7 million pet rabbits in the United States.
The injectable vaccine won’t help wild populations, though. “The stress induced by animal capture and manipulation is often lethal,” Joana Abrantes, a virus evolution specialist at the Research Centre in Biodiversity and Genetic Resources in Portugal, tells Science magazine.
Four institutions in Portugal are developing a vaccine that could be mixed into bait and fed to wild rabbits, per Science. But the vaccine development process could take at least three years, and then the vaccine would need to be given to wild populations every six months, making cost an issue.
Another possibility is that the virus will sweep through wild populations but leave behind naturally immune rabbits.
“We are still seeing live rabbits in areas where the outbreak has been going on for more than a month,” Arizona Game and Fish Department wildlife veterinarian Anne Justice-Allen tells Science. “So that is reassuring.”
The initial drop in bunny density could leave slim pickings for their predators, like golden eagles and foxes, but the naturally immune population that’s left behind would then do what bunnies do best: repopulate.