Evaluation of limiting factors of Oral Rabies Vaccinations (ORV) in wild canids, evidence from a field trial in Central Italy

Over the last few decades, Oral Rabies Vaccinations (ORV) has eliminated sylvatic rabies from most of Central andWestern Europe. Despite this success, they will probably be needed in the near future, due to the expansion of native and invasive reservoirs. It is unclear if they still work, at this time when many countries have an abundant wild boar population and complex assemblages of mammals. The ORV boasts a non-invasive and socially acceptable approach, but it presents some critical issues that we have analyzed in our study. Between November 2011 and March 2015, a total of 249 Rabigen® SAG2 VIRBAC baits were positioned on the ground at 5 sites in the study area. Baits were monitored by weekly inspections of camera traps. Overall, 63.4% of baits were found to have been worn after one week, mostly due to rainy weather, and had to be replaced. Remaining baits lasted on the field 3.66 1.07 days and 54.4% of them were consumed by wild boar (Sus scrofa). Our data highlight how a potential reservoir species such as the grey wolf did not ingest the vaccine baits while only few were taken by red fox, due to numerous competitors, especially wild boar. Findings raise doubts about the effectiveness of ORV in areas of Europe characterized by the presence of non-target species, particularly wild boar. The rising number in wild boar populations around Europe could seriously reduce baits presence in the environment, limiting their effectiveness. Future ORV campaigns against re-emerging rabies in Europe should either account for bait loss, or experiment with targeted forms of bait distribution, that prevent their uptake by non-target species.