Rabbit Hemorrhagic Disease Virus Type 2 (RHDV2)
Rabbit hemorrhagic disease (RHD) is caused by a virus in the calicivirus family. The first strains of rabbit hemorrhagic disease virus (RHDV) discovered in 1984 exclusively affected wild and domesticated European rabbits. Rabbits native to North America apparently were not susceptible to the previous two major viral subtypes: classical RHDV and RHDVa. A novel strain, RHDV2, was first found in Europe in 2010, and it spread to other parts of the world. The first North American detection of RHDV2 was in Canada in March 2018. It was then detected in domesticated or feral rabbits from several states within the USA over the next two years. It was uncertain if our wild rabbits would be susceptible to the RHDV2 strain. However, by spring of 2020, it was found to have apparently killed wild rabbits in New Mexico, Arizona, Colorado, Texas, and California. As such, we should assume our native eastern cottontail and swamp rabbits can be susceptible to RHDV2.
RHDV are highly contagious in rabbits. The virus enters the body through the mouth, nose, or eyes (mouth likely most common). The virus persists in the environment for long periods of time and is very resistant to deactivation. It is transmitted by direct contact with infected live or dead rabbits and likely through feces, urine, blood, respiratory secretions, and some insects and blood-feeding parasites. The virus may also be transmitted through contaminated food, water, and other materials in the environment. Humans may be able to move the virus on contaminated clothing or by transporting live or dead rabbits. It may be possible for scavengers and predators to move the virus after consuming infected rabbits, but information is still lacking on this. Rabbits that recover from the disease can shed the virus for at least a month. Humans, pets, and livestock other than rabbits are not susceptible to RHDV.
RHD may cause large-scale rabbit die-offs. Mortality rates from RHDV2 may range from 5 – 70% (20% average in experimentally infected rabbits). Similarly, Tularemia (bacterial disease) can also cause relatively large, localized mortality events. A possible field diagnostic for rabbits suspected to have died from RHD is presence of blood around the nose and mouth caused by internal bleeding, although this is not definitive and may not be present in all cases. Fresh carcasses should be submitted to a suitable laboratory for diagnostic examination and confirmation. However, precautions should be taken when handling rabbit carcasses to avoid spreading RHDV or possible Tularemia exposure (which does have human health implications). Presently, RHD vaccines are not readily available for application in domestic rabbit production in the USA.
Contact the MDWFP at (601) 432-2199 (Monday - Friday, 8 am - 5 pm) or email Rick.Hamrick@wfp.ms.gov if you find large numbers of dead rabbits with no apparent explanation for cause of death. Particularly since this is a relatively new disease, state wildlife agencies are monitoring for presence of RHDV2. For more on RHDV2 best management practices for domestic rabbit keepers, refer to Mississippi Board of Animal Health's Rabbit Hemorrhagic Disease resources.