Serology of rabbit haemorrhagic disease virus in wild rabbits before and after release of the virus in New Zealand

Rabbit haemorrhagic disease virus (RHDV) was illegally released in New Zeal and in August 1997. The initial release and spread of the virus was conduct ed by landholders in an effort to reduce costs associated with more convent ional control methods (poisoning and shooting). Serum was collected from wi ld rabbits throughout the Otago region prior to the release and from 13 sit es in the months following the first epizootic. Following the occurrence of the first RHDV epizootic on 13 pastoral fanning properties a range of surv ival rates was found. The major factor influencing the survival rate was fo und to be the method of release, with widespread use of carrot or oat baits containing RHDV resulting in poor kills. Widespread use of baits also resu lted in higher levels of antibody in surviving adult rabbits with a higher proportion of adult females surviving the epizootic, compared with properti es where the disease was allowed to spread naturally. A correlation was fou nd between survival rate and the percentage of surviving adults with high l evels of antibody. These results suggest that poor kill rates are not due t o poor spread of the virus, that the large-scale use of baits resulted in p rotective immunisation and that rabbit control should in the future be achi eved through establishing naturally spreading epidemics rather than widespr ead use of baits. (C) 1999 Elsevier Science B.V. All rights reserved.