Differences between RHDV1 and RHDV2

RHDV2 has replaced RHDV1 in many parts of the world and has reached epidemic proportions in many countries where it poses a serious ecological and economic threat. There are several important differences between RHDV1 and RHDV2 that make RHD2 more serious than RHD1.

• Lack of cross immunity: There is little or no cross immunity between RHDV1 and RHDV2 so rabbits that are vaccinated against or have recovered from RHDV1 are still susceptible to RHDV2.
• Susceptibility of different species of rabbits: Wild rabbits act as a reservoir of infection for domestic rabbits. RHDV1 only affects the European Rabbit (Oryctolagus cuniculus). RHDV2 also affects hares. Cottontails (Sylvilagus floridanus) and Black-tailed Jackrabbits (Lepus californicus) also appear to be susceptible to RHDV2.
• Susceptibility of baby rabbits: A feature of RHDV1 is that baby rabbits have a natural immunity to the disease. Most rabbits under 8 weeks of age remain unaffected by RHDV1. They can develop a life-long immunity if their immune system is challenged by exposure to the disease although unexposed rabbits become increasingly susceptible until 6–10 weeks of age when the physiological resistance to the virus disappears. Age immunity allows rabbits to survive RHDV1 so wild populations can become immune. This is not the case with RHDV2, which affects rabbits of all ages. There is no age immunity so the disease can wipe out wild populations only leaving a few, possibly genetically resistant, individuals.