Oral rabies vaccination in north america: opportunities, complexities, and challenges

Abstract

Steps to facilitate inter-jurisdictional collaboration nationally and continentally have been critical for implementing and conducting coordinated wildlife rabies management programs that rely heavily on oral rabies vaccination (ORV). Formation of a national rabies management team has been pivotal for coordinated ORV programs in the United States of America. The signing of the North American Rabies Management Plan extended a collaborative framework for coordination of surveillance, control, and research in border areas among Canada, Mexico, and the US. Advances in enhanced surveillance have facilitated sampling of greater scope and intensity near ORV zones for improved rabies management decision-making in real time. The value of enhanced surveillance as a complement to public health surveillance was best illustrated in Ohio during 2007, where 19 rabies cases were detected that were critical for the formulation of focused contingency actions for controlling rabies in this strategically key area. Diverse complexities and challenges are commonplace when applying ORV to control rabies in wild meso-carnivores. Nevertheless, intervention has resulted in notable successes, including the elimination of an arctic fox (Vulpes lagopus) rabies virus variant in most of southern Ontario, Canada, with ancillary benefits of elimination extending into Quebec and the northeastern US. Progress continues with ORV toward preventing the spread and working toward elimination of a unique variant of gray fox (Urocyon cinereoargenteus) rabies in west central Texas. Elimination of rabies in coyotes (Canis latrans) through ORV contributed to the US being declared free of canine rabies in 2007. Raccoon (Procyon lotor) rabies control continues to present the greatest challenges among meso-carnivore rabies reservoirs, yet to date intervention has prevented this variant from gaining a broad geographic foothold beyond ORV zones designed to prevent its spread from the eastern US. Progress continues toward the development and testing of new bait-vaccine combinations that increase the chance for improved delivery and performance in the diverse meso-carnivore rabies reservoir complex in the US.

Figure 1. Raccoon oral rabies vaccination and Wildlife Services' enhanced surveillance counties in the United States of America, 2007.

Figure 2. Raccoon variant rabies cases in Ohio contingency action zone.

Since 16 July 2004 when raccoon rabies virus variant was first detected west of the existing oral rabies vaccination zone, 117 animals have been confirmed positive with raccoon variant within the contingency action zone. In 2007, no cases were detected via the public health surveillance system, illustrating the need for enhanced rabies surveillance.

Figure 3. Contingency actions in Ohio, 2008.

A large-scale trap-vaccinate-release (TVR) operation was conducted near Cleveland, Ohio, in 2008 and resulted in the hand vaccination of 4,196 raccoons and the brainstem testing of 138 raccoons and 77 skunks. The TVR zone consisted of 185 cells (1 km² in size) and was delineated from raccoon variant rabies cases confirmed in the Contingency Action ORV zone in 2007 (n = 19). In addition to TVR, oral rabies vaccine baits were distributed over the area as part of contingency actions in 2008.

Figure 4. Percent positive rabies antibody response (≥0.05 IU).