A cross-sectional study of risk factors affecting the outcome of rabbit haemorrhagic disease virus releases in New South Wales.
OBJECTIVE
To determine what factors governed the extent of outbreaks of rabbit haemorrhagic disease (RHD) following releases in New South Wales.


METHODS
Retrospective cross-sectional study.


METHODS
Information from the data set of official releases was subjected to two preliminary analyses. More comprehensive information on a subsample of official RHD releases, sites and animals was gathered by telephone survey of Rural Lands Protection Board staff and farmers. Data were analysed using multivariate techniques to determine which factors were associated with rabbit mortality within one month of RHDV release, within several months of release and in affecting the proportion of the population killed.


RESULTS
A strong association was found between the presence of heavy flea infestation (odds ratio 2.7), breeding in rabbits and outbreaks of RHD. For each week following breeding there was an 8% decline in the odds of an outbreak. Low temperatures also promoted outbreaks. Less important effects included the prior presence of RHD at the release site, which reduced the likelihood and severity of outbreaks. The presence of cattle and proximity to the nearest water body were associated with increased severity and likelihood of outbreaks respectively.


CONCLUSIONS
Both breeding of rabbits and associated high flea numbers may act together or independently in promoting outbreaks of RHD. Stresses involved with rabbit reproduction and low environmental temperatures also appear to influence the likelihood of outbreaks. The effects of proximity to cattle and water suggests that both flies and mosquitoes may have a minor role in local transmission.
Lugton
I W
IW
NSW Agriculture, Vertebrate Pest Research Unit, Orange.
D000818:Animals; D017250:Caliciviridae Infections / Q000453:epidemiology / Q000635:transmission / Q000662:veterinary*; D002417:Cattle; D003430:Cross-Sectional Studies; D004196:Disease Outbreaks / Q000662:veterinary; D004478:Ectoparasitic Infestations / Q000453:epidemiology / Q000662:veterinary; D017929:Hemorrhagic Disease Virus, Rabbit / Q000302:isolation & purification*; D007303:Insect Vectors; D016015:Logistic Models; D009517:New South Wales / Q000453:epidemiology; D011817:Rabbits; D012189:Retrospective Studies; D012307:Risk Factors; D005423:Siphonaptera; D011795:Surveys and Questionnaires