Enhancing rabies surveillance for the oral vaccination of carnivores

Laboratory-based surveillance is critical for a basic understanding of the spatial distribution and temporal abundance of wildlife diseases, as well as a prerequisite for measuring the relative success of prevention and... [ view full abstract ]

Laboratory-based surveillance is critical for a basic understanding of the spatial distribution and temporal abundance of wildlife diseases, as well as a prerequisite for measuring the relative success of prevention and control efforts. From a global perspective, rabies remains a neglected viral zoonosis, in which surveillance is key to determination of the disease burden among humans, domestic species and wildlife. Modern definitive animal rabies diagnosis is dependent upon detection of viral antigens within neurons of CNS tissues collected post-mortem, using the direct fluorescent antibody (DFA) test. Routine public health rabies surveillance is concentrated primarily upon samples from animals which expose humans. Within North America, current oral rabies vaccination (ORV) programs are dependent upon both existing public health and local enhanced surveillance. Enhanced wildlife rabies surveillance involves only those samples that do not have either a human or domestic animal exposure history and are focused on selected reservoir and vector species exhibiting aberrant behavior, as well as upon road-killed specimens. Our objective was to evaluate a direct rapid immuno-histochemical test (DRIT), developed as a method to assist wildlife biologists during enhanced surveillance applications during ORV activities. The DRIT uses antibodies conjugated to biotin in a streptavidin-peroxidase system to detect viral inclusions within formalin-fixed touch impressions of brainstem samples obtained from suspect animals, via light microscopy, in approximately one hour. During the past decade, more than 75,000 samples from wild carnivores have been evaluated within North America. To date, the comparative sensitivity and specificity of the DRIT approached similar levels to the DFA test. The DRIT appears as one example of an effective, economical, safe, local point-of-collection, anatomic-pathologic-based diagnostic test suitable for pathogen discovery, enhanced surveillance and evaluation of ORV programs. Application of such laboratory-based surveillance systems will be fundamental towards any future wildlife rabies elimination plan among free-ranging carnivores.