A close look at RHDV2

We often get asked about the differences between RHDV1 and RHDV2. When RHDV2 was first reporting in Europe, several studies reported that it appeared to be less virulent than RHDV1, causing disease in fewer individuals and over a longer time period. Yet that certainly hasn’t been consistent with our observations in Australia.

To properly evaluate this, we looked at the effects of the Australian RHDV2 variant (actually a European RHDV1/RHDV2 recombinant – see this post for more information on recombinants) in both younger (5-week-old) and older (11-week-old) rabbits at two different infectious doses. We found that RHDV2 was highly lethal, resulting in death of all infected rabbits within 71 hours after infection. We found that young rabbits and those infected with a high virus dose succumbed faster than older rabbits or those infected with a lower virus dose. The clinical signs that we observed after RHDV2 infection included fever, lethargy, weight loss, and terminal seizures (likely due to low blood glucose), consistent with signs seen after RHDV1 infection but occurring over a shorter time period. We were able to track clinical signs really effectively by using continuous temperature monitoring collars, ‘FitBark’ devices to track activity levels/lethargy, and continuous video camera monitoring. This is the first time such continuous monitoring devices have been used to assess welfare impacts in rabbits, to the best of our knowledge. This showed that clinical signs were quite subtle until just prior to death. Importantly, this work was done in domestic/laboratory rabbits and the impacts may be different in wild rabbits or those with some level of pre-existing immunity.

This work demonstrates that the Australian RHDV2 variant is highly virulent in susceptible rabbits, especially in kits or in animals infected with a high virus dose. Previous reports suggesting that RHDV2 has low or intermediate virulence may have used different RHDV2 variants, animals of different ages or genetic backgrounds, or lower virus doses. You can read the full report here.