The effect of rabbit population control programmes on the impact of rabbit haemorrhagic disease in south‐eastern Australia

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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.

European rabbit survival and recruitment are linked to epidemiological and environmental conditions in their exotic range

“…The relative importance of disease is unsurprising considering observations of declining densities of O. cuniculus in their native range since the arrival of RHD (Delibes-Mateos et al 2008b, 2009; and the usefulness of viral biocontrol agents in controlling rabbit abundance in exotic habitats (Mutze et al 2002(Mutze et al , 2010). Yet, importantly, we show that myxomatosis, in addition to RHD, influences survival probabilities of younger rabbits, but not older rabbits, suggesting a complex disease response among populations of native O. cuniculus on the Iberian Peninsula, as well as in its exotic range.…”

“…We hypothesized a priori that (i) environmental, competition and disease conditions impact age-classes (<3 months, 3-6 months, >6 months) in different ways; (ii) mean daily temperature can negatively influence rabbit survival (Cooke 1977); (iii) rainfall can directly impact survival (Bowen & Read 1998), or through a positive interaction with pasture biomass (Poole 1960); (iv) RHD and myxomatosis outbreaks negatively impact rabbit survival and abundance (Mutze et al 2002); (v) the proportion of rabbits without antibodies (i.e. sero-negative) to the RHD and myxoma viruses negatively influences rabbit survival rates (Mutze et al 2010) -antibody status was tested and classified using a panel of four RHD virus antibody ELISAs (Cooke et al 2000) and a myxoma antibody ELISA (Kerr 1997); (vi) rabbit population density can negatively impact survival through agnostic encounters with other rabbits or increased intraspecific competition for food; and can positively impact survival through an interaction with disease (because disease related mortality rates can be higher in low density populations; Calvete 2006); (vii) season can influence survival by impacting disease prevalence (Mutze et al 2010); and (viii) the severity of disease outbreaks among older rabbits is regulated by time since last outbreak and the proportion of young and old animals in the population. Number of trapping days in a trapping session and individual weight at first capture were identified as covariates on recapture probabilities.…”

“…Since important drivers of rabbit survival are probably age dependent (e.g. epidemiological processes; Mutze et al 2010) we initially determined the 'best' environmental, competition and disease model for each age-class, using AICc to rank models in terms of parsimony (Burnham & Anderson 2002). We did this by constraining the focal age-class to specific model covariates, while simultaneously treating the non-focal age-classes as time variable (i.e.…”

Comparative quantitative monitoring of rabbit haemorrhagic disease viruses in rabbit kittens

“…In recent years rabbit populations have recovered [16] potentially due to a combination of high levels of population immunity to RHDV-v351 [17-19], rabbits developing genetic resistance against the virus [20,21] and the presence of a non-pathogenic rabbit calicivirus acting as an imperfect natural vaccine [22,23]. …”

Recolonisation of rabbit warrens following coordinated ripping programs in Victoria, south-eastern Australia

“…However, ripping operations in the present study occurred following the escape and controlled release of RHDV in 1995-96, when rabbit numbers were supressed by the initial epizootic (Mutze et al 2010). Consequently, the capacity of populations to recover following the ripping operations was likely to have been impaired compared with a pre-RHD environment.…”