Bait uptake by foxes (Vulpes vulpes) in urban Melbourne: the potential of oral vaccination for rabies control

Red foxes (Vulpes vulpes) are widely distributed throughout the Melbourne m etropolitan area. Density estimates indicate that fox populations would be capable of maintaining the endemic persistence of rabies. Oral vaccination of foxes by baiting is a technique that has been used successfully overseas to manage rabies epizootics. This study assessed the uptake by foxes of ba its containing biomarkers in three urban field sites in winter 1993 and sum mer 1993/94. Baits were dosed with 200 mg of tetracycline in the winter tri al and 5 mg of iophenoxic acid in the summer trial, and distributed at a de nsity of 8 baits ha(-1) in open areas within each field site. In the winter trial, 8 of 11 (72.7%) radio-collared foxes known to be in the field sites during the distribution of baits were marked. In the summer trial, 45 of t he 49 foxes (92%) recovered from the combined field sites had consumed at l east a single bait, resulting in bait acceptance of 80-97% for each field s ite. No bias existed between plasma iodine levels due to sex, although firs t-year foxes had a significantly higher level than older age groups combine d. There were no significant differences in mean age of foxes collected at the three field sites, yet significant differences existed in mean plasma i odine concentrations between all three sites. These results are discussed w ith reference to rabies contingency planning. The high rates of bait uptake in this study are encouraging and suggest that oral vaccination may be a v iable strategy for rabies containment in urban areas and is worthy of furth er assessment at reduced baiting densities.