Prolonged decline in the abundance of wild European rabbits Oryctolagus cuniculus and high immunity level over three years following the arrival of rabbit haemorrhagic disease

Abstract

A free-living population of European rabbits Oryctolagus cuniculus was monitored over three years, from 1996 to 1998, following the arrival of rabbit haemorrhagic disease (RHD) in 1995. The survey was based on nocturnal observations of individually marked rabbits to determine population size and on blood collection to determine whether rabbits carried RHD antibodies. We directly confirmed RHD outbreaks by examination of dead rabbits and detection of RHD virus (RHDV). Only one further recurrence of RHD was detected by this method, in 1996. Contrary to the initial outbreak, this second occurrence did not result in a major decrease in population size. No direct evidence of other outbreaks was detected in 1997 and 1998. However, the sparse data did not enable us to conclude that RHD was absent. Indeed, seroconversions in individual rabbits were noticed throughout the three years and the level of population immunity remained high, proving that either RHDV or RHD-like viruses were present in the population. The influence of age, year and quarter on the serological status of the rabbits were analysed using a log-linear model. The selected model showed that the proportion of rabbits with RHD antibodies varied with year and period of the year. Three years after the first occurrence of RHD, the population had not recovered to its level prior to the first outbreak. We assumed that predation by red foxes could be partly responsible for keeping the population low.