Antibody status and survival of Australian wild rabbits challenged with rabbit haemorrhagic disease virus

In Australia, the epidemiology of rabbit haemorrhagic disease virus (RHDV) is complicated by nonpathogenic forms of calicivirus (bCV) co-circulating with RHDV and providing variable protection from RHDV. Currently no bCV virus-specific antibody tests exist; however, a series of four ELISAs used to detect antibodies to RHDV provided an indirect means to detect antibodies to bCV, enabling antibody categories of seronegative, maternal RHDV, RHDV or bCV to be determined. Rabbits (188) from four locations were challenged with RHDV and logistic regression models determined that, for rabbits <15 months old, survival was dependent on antibody titres alone and the relationship did not vary with age, capture site, gender, liveweight or reproductive status. All rabbits survived challenge after reaching 15 months of age, irrespective of their antibody titres. Where bCV antibodies were prevalent in young rabbits, the bCV category did not adequately summarise all information about rabbit survival that can be obtained from antibody titres. Within antibody categories, 95% of rabbits with RHDV, 33% with bCV, 40% with maternal RHDV and 22% with seronegative antibodies survived. The high survival rate of adults implies that natural outbreaks or controlled releases of RHDV will have little impact on adult breeding rabbits. Therefore, where RHDV and bCV are endemic, conventional rabbit-control programs targeting the immune breeding populations should provide the most predictable outcome for long-term maintenance of low rabbit populations.