Rabbit hemorrhagic disease confirmed for the first time in endangered riparian brush rabbits
On May 20, 2022, California Department of Fish and Wildlife (CDFW) veterinary staff were notified that an endangered riverine bush rabbit found deceased in the San Joaquin River National Wildlife Refuge, had tested positive for the CDFW virus. Rabbit Hemorrhagic Disease 2 (RHDV2), a highly transmissible and often fatal disease of rabbits. The disease spread rapidly in the western United States.
“This is a finding we hoped would never happen, but it’s one we anticipated by implementing a proactive vaccination effort,” said CDFW Senior Wildlife Veterinarian Dr. Deana Clifford. “We are in the very early stages of understanding the impacts on the species now that RHDV2 has arrived at the refuge.”
Since August 2020, a multi-partner team has been vaccinating riverine wild rabbits to protect a portion of the population at the San Joaquin River National Wildlife Refuge and adjacent habitat. The team – US Fish and Wildlife Service (USFWS), CDFW, the Oakland Zoo, River Partners, California State University, Stanislaus, California Department of Food and Agriculture and UC Davis California Animal Health and Food Safety Lab – undertook a ambitious program that safely administered the Filavac RHDV2 vaccine to 638 rabbits.
“This will be the true test of the effectiveness of our vaccination efforts, which are part of a larger conservation effort to restore habitat and recover the population of riparian brush rabbits,” said Kim Forrest, head of the USFWS San Luis National Wildlife Refuge Complex.
Riparian brush rabbits are found in small patches of remnant riparian forest and shrub habitat in the northern part of the San Joaquin Valley and the Sacramento-San Joaquin Delta. Because vaccinations require trapping and giving injections to each individual rabbit, it is not possible to deploy vaccinations for wild rabbit populations except in cases where populations are small and at risk. CDFW has received reports that live rabbits are still being seen in other areas of the state where the virus has been present since 2020, giving biologists hope that some rabbits are surviving the infection.
Although the impact of RHDV2 on the endangered riparian brush rabbit is not yet known, biologists are closely monitoring the rabbits using camera surveys, continuing to administer vaccinations and testing to determine if other cases are occurring at the refuge or in adjacent habitat.
“The vaccine has been shown to be very effective against the virus in domestic rabbits, and it is hoped that over time some of the riverine brush rabbits will become immune and survive,” Clifford said.
RHDV2 was first observed in wild rabbits in the southwestern United States in March 2020, and since then it has rapidly spread to many states. In California, cases of the virus in wild rabbits have been detected in Alameda, Kern, Los Angeles, Orange, Riverside, San Bernardino, San Benito and San Diego counties. Cases in domestic rabbits have also been confirmed in Fresno, Sonoma, Ventura and San Louis Obispo counties. RHDV2 is unrelated to the novel coronavirus and does not affect humans or pets other than rabbits.
The public can help by reporting any sick or dead wild rabbits to CDFW as wildlife veterinarians continue to monitor the situation. Anyone who lives, works, or recreates in wild rabbit habitat can report sightings of sick or dead rabbits to the CDFW Wildlife Health Lab at (916) 358-2790, or file a mortality report online. through the CDFW website.
CDFW’s RHDV2 webpage includes fact sheets and information about the virus, how to report sightings of dead rabbits, strategies to prevent the spread of human-induced illness, a link to CDFA resources for owners of domestic rabbits and an interactive map from the United States Department of Agriculture. showing counties where the disease has been confirmed in domestic, feral and/or feral rabbits.
Ken Paglia, CDFW Communications, (916) 825-7120
Jackie D’Almeida, U.S. Fish and Wildlife Service, (916) 207-8385
Photo: courtesy of USFWS