The calicivirus (RHDV) causing rabbit haemorrhagic disease (RHD) is endemic in the UK but its rate of spread, recurrence and impact on wild rabbit populations are unknown, as are its relationships with avirulent RHDV and myxoma virus. In this study, laboratory tests (including ELISA) to detect RHD antibodies to the virulent and avirulent forms in rabbits will be developed and the influence of myxoma virus on RHDV pathogenicity will be investigated, thus enabling development of a multi-pathogen model. Tests for detecting RHD and myxomatosis antibodies will also be developed. The avirulent form of the virus will be isolated and partially sequenced and attempts will be made to propagate RHDV in laboratory rabbits. Temporal data on the movement of RHDV through susceptible/partially susceptible populations will be collected. To examine the influence of myxomatosis on the pathogenicity of RHDV, rabbits seropositive for RHDV or infected experimentally will be studied in conjunction with field studies. Reports of the spread of RHD will be collated and field studies will monitor the impact of RHDV in rabbit populations in order to predict changes in populations, and hence damage to agriculture, and to determine whether a seasonal cycle of immunity to RHDV and to myxomatosis occurs. A number of sites will be monitored, including those confirmed with RHD; serological studies of rabbit carcasses, and live trapping and repeated sampling of several wild rabbit populations will be performed, providing an opportunity to study the epidemiology of RHDV and myxomatosis in a population of individually tagged rabbits of known sex and age. Data will include seasonal effects in the same individuals, longevity of immunity, temporal association with myxomatosis and whether or not repeated removal sampling biases results. Evidence of whether the disease is endemic or has died out will be collected, and population recovery and further outbreaks will be monitored. Individual- and population-based models will be developed to understand the epidemiology and interaction of virulent RHDV with the avirulent strain and myxoma virus, together with a model for predicting the future impact and spread of the disease. Results will assist in policy decisions relating to rabbit management and will also assist in the development of the MAFF rabbit population model.