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Rabbit hemorrhagic disease virus type 2 (RHDV2), a Lagovirus in the family Caliciviridae, has caused substantial mortality in wild lagomorph (rabbit and hare) populations in North America. Researchers have been studying how management actions can help wild rabbit and hare populations respond to the virus.

Why this matters: Rabbit hemorrhagic disease virus type 2 poses a threat to wild rabbit and hare populations in North America. Of particular concern are threated and endangered species such as the riparian brush rabbit. A new study (Russell et al. 2024) models the response these populations may have to RHDV2 and vaccination and how this management action could aid in their continued recovery.

Riparian brush rabbit on moss ground.
San Joaquin River Riparian Brush Rabbits, San Luis National Wildlife Refuge, CA. Photo by Lee Eastman/USFWS.

Since RHDV2’s initial detection in wild rabbits in the southwestern United States and adjacent northwestern Mexico in 2020, concern has developed regarding RHDV2’s potential population level impacts, particularly to threatened and endangered species and subspecies. To date, RHDV2 has been confirmed in seven North American wild lagomorph species in 14 U.S. states (USDA APHIS 2023), in addition to multiple jurisdictions in Mexico.

The riparian brush rabbit (Sylvilagus bachmani riparius) is a federally endangered subspecies of brush rabbit (S. bachmani), whose range is limited to specific riparian corridors in the northern San Joaquin Valley of California. Due to their endangered species status and limited geographic range (three known remnant populations), RHDV2 poses a substantial threat to their continued recovery and vaccination against the virus is being implemented by the U.S. Fish and Wildlife Service and partners. To help inform vaccination strategies, Russell et al. (2024) modeled the effects of RHDV2 introduction on riparian brush rabbits and simulated varying levels of vaccination against RHDV2 as a management intervention. Using a range of parameters, an initial population size of ~1,500 rabbits, and continued RHDV2 exposure, the model estimated a surviving population of 538 rabbits after one year with a 0-10% vaccination rate. At the highest modeled vaccination rate of 30-40%, the estimated surviving population after one year was 774 rabbits. Given the resources necessary to implement and maintain an intensive injection-based vaccination program for RHDV2 in wild rabbits, especially given their relatively short lifespan, these strategies are most likely to be successful in small target populations where high vaccination rates can be maintained.

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