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

Abstract

Red foxes (Vulpes vulpes) are widely distributed throughout the Melbourne metropolitan 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 baits containing biomarkers in three urban field sites in winter 1993 and summer 1993/94. Baits were dosed with 200 mg of tetracycline in the winter trial and 5 mg of iophenoxic acid in the summer trial, and distributed at a density 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 the 49 foxes (92%) recovered from the combined field sites had consumed at least a single bait, resulting in bait acceptance of 80–97% for each field site. No bias existed between plasma iodine levels due to sex, although first-year foxes had a significantly higher level than older age groups combined. There were no significant differences in mean age of foxes collected at the three field sites, yet significant differences existed in mean plasma iodine concentrations between all three sites. These results are discussed with reference to rabies contingency planning. The high rates of bait uptake in this study are encouraging and suggest that oral vaccination may be a viable strategy for rabies containment in urban areas and is worthy of further assessment at reduced baiting densities.