Rabbit haemorrhagic disease: does a pre-existing RHDV-like virus reduce the effectiveness of RHD as a biological control in Australia?

Serological data from wild rabbits support the hypothesis that a second RHDV-like virus was already present in Australia before rabbit haemorrhagic disease virus (RHDV) was introduced as a biological control agent. This putative virus apparently persists in most wild rabbit populations in the presence of RHDV, and antibodies raised against it appear to protect some rabbits from fatal rabbit haemorrhagic disease (RHD). High titres of these antibodies are most commonly found in rabbits from high rainfall areas; this may explain why the initial mortality from RHD declined as the disease spread from dry areas into wetter regions and why it remains less effective as a biological control in wetter regions today. The implications for further advances in rabbit control are discussed, including the need to isolate this putative RHDV-like virus and develop specific ELISA tests to facilitate its detection in the field.