The effect of rabbit population control programmes on the impact of rabbit haemorrhagic disease in south-eastern Australia.
The effect of rabbit population density on transmission of rabbit haemorrhagic disease virus (RHDV) is a critical aspect of disease ecology for rabbit control and rabbit conservation. We examined the interaction between rabbit control and spread of RHDV and a non-pathogenic calicivirus (bCV) in Australian wild rabbit populations, and reviewed existing recommendations for control in this context. Rabbits were sampled at eight pairs of sites; from rabbit populations where densities had been reduced by conventional control and from matching uncontrolled populations. Sites chosen ranged from hot, arid areas where RHDV had greatly reduced rabbit numbers to cooler, higher-rainfall areas where rabbits remained more abundant. Virus activity was implied from antibody profiles in sera of surviving rabbits. Reducing population density by conventional control had a similar effect on disease transmission despite a seven-fold difference in initial density. Populations reduced by 70% or more had lower RHDV antibody prevalence in juvenile rabbits but not in adult rabbits, indicating that reducing rabbit density slowed but did not stop RHDV transmission. We found no interactions between rabbit control, RHDV and bCV that could be exploited to improve rabbit management. Synthesis and applications. Delayed RHDV infection in rabbit control sites is likely to be offset by higher mortality in older rabbits, so that conventional rabbit control does not reduce the impact of RHDV on rabbit populations. Only minor changes to delay the timing of summer rabbit control programmes in cooler areas of Australia are necessary to take best advantage of RHDV-induced reduction in rabbit numbers. For conservation management of rabbits in Europe, these findings indicate that RHDV may continue to have a severe impact on rabbit populations that have been reduced to low population density, but also raise the possibility that bCVs might be introduced to rabbit populations to aid their recovery.