Rabbit Hemorrhagic Disease in British Columbia
In mid-February 2018 feral rabbits were found dead in small numbers on a university campus in Nanaimo and all the rabbits in a small feral colony on Annacis Island in Delta were found dead. Upon necropsy examination of these rabbits CWHC pathologist Hein Snyman noted widespread acute hepatocellular necrosis (Fig. 1), disseminated lymphocyte karyorrhexis and necrosis in the spleen and visceral lymph node, scattered acute renal tubular necrosis, and variably present intra-glomerular thrombi; all typical lesions of Rabbit Hemorrhagic Disease (RHD) (Fig. 2). This diagnosis was confirmed with PCR for Rabbit Hemorrhagic Disease Virus and sequencing of the PCR product was consistent with RHDV. RHDV was also confirmed through independent PCR testing and other ancillary diagnostic testing (electron microscopy, rabbit inoculation) of duplicate tissue samples from these rabbits by the CFIA at the National Centre for Foreign Animal Disease (NCFAD) in Winnipeg.
Rabbit hemorrhagic disease, sometimes referred to as “bunny Ebola”, is an extremely contagious viral disease of domesticated and wild European rabbits with a mortality rate that often reaches 100% in unvaccinated European rabbits (Oryctolagus cuniculus). It can be readily transmitted by direct contact with live or dead animals, and on fomites. Since the initial diagnosis there have been reports of large numbers of dead feral rabbits around Nanaimo and a few in the lower mainland.
There are many strains of RHDV, with three major viral subtypes recognised: RHDV (classical RHDV), a related antigenic variant RHDVa, and a recently emerged strain RHDV2 (also called RHDVb). Whole genome next generation sequencing by NCFAD of the virus from the BC rabbits most closely matched (93% identity) an RHDV-2 isolate from an outbreak in a rabbit farm in Navarra, Spain in 2011. The origin of the virus in BC is unknown.
RHDV2 was first identified in France in 2010, and since then has spread throughout Europe, replacing the circulating RHDV/RHDVa strains in most European countries. Its antigenic profile is quite different from that of classical RHDV and while classical RHDV spares rabbits younger than 6-8 weeks, RHDV2 affects rabbits of all ages. In Europe, RHDV2 tends to have a lower mortality rate than classical RHDV (5 to 70% vs. 80-90% lethality). In BC, however, the ongoing mortality rate has reached 90 to 100% in feral colonies and several affected commercial rabbitries.
This is the third confirmed diagnosis of Rabbit Hemorrhagic disease in Canada, the first in BC, and by far the largest reported outbreak of RHD in North America. It is the first outbreak to involve RHDV2 in North America.
Since the initial diagnosis, 20/35 cases submitted for testing for RHDV have been positive. Positive cases have been detected in feral European rabbits, pet rabbits and meat rabbits from Nanaimo, Delta, Courtenay/Comox, Richmond, Coombs, Parksville and Ladysmith.
So far, only European rabbits (Oryctolagus cuniculus) have been affected in BC. This is consistent with the experience in other parts of the world where other lagomorphs generally seem to be unaffected by classical RHDV/RHDVa. However, it is the first RHDV2 outbreak in North America so there is very limited information pertaining to the specific susceptibility or resistance of wild rabbit species that are prevalent in British Columbia. No native rabbits are present on Vancouver Island where the majority of the outbreak has occurred but invasive Eastern cottontails rabbits in the area do not yet appear to be affected.
A vaccine has been brought in on Emergency Drug Release from France by the BC Ministry of Agriculture for use in domestic rabbits. For more information on vaccine availability and how to protect domestic rabbits consult with your veterinarian.