Evaluation of rabies virus characterization to enhance early detection of important rabies epizootic events in the United States.

OBJECTIVE: To evaluate rabies virus (RABV) characterization data obtained from animal specimens submitted to the US public health rabies surveillance system and propose a standardized approach to sample selection for RABV characterization that could enhance early detection of important rabies epizootic events in the United States. SAMPLE: United States public health rabies surveillance system data collected from January 1, 2010, through December 31, 2015. PROCEDURES: Data were reviewed to identify RABV-positive specimens for which virus characterization would likely provide information regarding any of 4 overarching events (discovery of novel variants, translocation of RABV variants, host-shift events, and any unusual rabies-related event) that could substantially alter animal rabies epizootiology in the United States. These specimens were designated as specimens of epizootiological importance (SEIs). Estimates of the additional number of specimens that public health laboratories could expect to process each year if all SEIs underwent RABV characterization were calculated. RESULTS: During the 6-year period, the mean annual number of SEIs was 855 (95% CI, 739 to 971); the mean number of SEIs that underwent virus characterization was 270 (95% CI, 187 to 353). Virus characterization of all SEIs would be expected to increase the public health laboratories' test load by approximately 585 (95% CI, 543 to 625) specimens/y. CONCLUSIONS AND CLINICAL RELEVANCE: Prioritization of RABV characterization of SEIs may improve early detection of rabies events associated with RABV host shifts, variant translocations, and importation. Characterization of SEIs may help refine wildlife rabies management practices. Each public health laboratory should evaluate testing of SEIs to ensure diagnostic laboratory capacity is not overstretched.

Field Studies Evaluating Bait Acceptance and Handling by Dogs in Navajo Nation, USA.

Mass parenteral vaccination remains the cornerstone of dog rabies control. Oral rabies vaccination (ORV) could increase vaccination coverage where free-roaming dogs represent a sizeable segment of the population at risk. ORV's success is dependent on the acceptance of baits that release an efficacious vaccine into the oral cavity. A new egg-flavored bait was tested alongside boiled bovine intestine and a commercially available fishmeal bait using a hand-out model on the Navajo Nation, United States, during June 2016. A PVC capsule and biodegradable sachet were tested, and had no effect on bait acceptance. The intestine baits had the highest acceptance (91.9%; 95% confidence interval (CI), 83.9%⁻96.7%), but the fishmeal (81.1%; 95% CI, 71.5%⁻88.6%) and the egg-flavored baits (77.4%; 95% CI, 72.4%⁻81.8%) were also well accepted, suggesting that local bait preference studies may be warranted to enhance ORV's success in other areas where canine rabies is being managed. Based on a dyed water marker, the delivery of a placebo vaccine was best in the intestine baits (75.4%; 95% CI, 63.5%⁻84.9%), followed by the egg-flavored (68.0%; 95% CI, 62.4%⁻73.2%) and fishmeal (54.3%; 95% CI, 42.9%⁻65.4%) baits. Acceptance was not influenced by the supervision or ownership, or sex, age, and body condition of the dogs. This study illustrates that a portion of a dog population may be orally vaccinated as a complement to parenteral vaccination to achieve the immune thresholds required to eliminate dog rabies.

Progress towards Bait Station Integration into Oral Rabies Vaccination Programs in the United States: Field Trials in Massachusetts and Florida.

Bait stations for distribution of oral rabies vaccine baits are designed for rabies management in highly-developed areas where traditional distribution of oral rabies vaccine baits may be difficult. As part of national efforts to contain and eliminate the raccoon (Procyon lotor) variant of the rabies virus (raccoon rabies) in the eastern United States, the United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services program, distributed vaccine baits by bait stations experimentally and operationally in Massachusetts during 2006-present, and in Florida during 2009⁻2015. In Massachusetts, a rabies virus-neutralizing antibody (RVNA) response of 42.1% for raccoons captured in areas baited with high density bait stations during 2011⁻2015 was achieved, compared with 46.2% in areas baited by hand, suggesting the continuation of this as a strategy for the oral rabies vaccination (ORV) program there, and for similar locations. Non-target competition for vaccine baits is problematic, regardless of distribution method. In Massachusetts, bait station visitation rates for targeted raccoons and non-target opossums (Didelphis virginiana) were similar (1.18:1) during 2006⁻2009 (p > 0.05). Bait station modifications for reducing non-target uptake were tested, and in Massachusetts, reduced non-target bait access was achieved with two design alternatives (p < 0.001). However, no difference was noted between the control and these two alternative designs in Florida. Due to ongoing trials of new vaccines and baits, the bait station performance of an adenovirus rabies glycoprotein recombinant vaccine bait, ONRAB® bait (Artemis Technologies, Guelph, ON, Canada) and a vaccinia-rabies glycoprotein recombinant vaccine bait, RABORAL V-RG®bait (Merial Limited, Athens, GA, USA), was compared. While uptake of the ONRAB bait was greater in Massachusetts (p < 0.001) in this limited trial, both types performed equally well in Florida. Since bait station tampering or theft as well as potential human bait contacts has been problematic, performance of camouflaged versus unpainted white bait stations was analyzed in terms of internal temperatures and maintaining a stable bait storage environment. In Massachusetts, camouflaged bait station interiors did not reach higher average temperatures than plain white bait stations in partially- or fully-shaded locations, while in Florida, camouflaged bait stations were significantly warmer in light exposure categories (p < 0.05). As ORV operations expand into more heavily-urbanized areas, bait stations will be increasingly important for vaccine bait distribution, and continued refinements in the strategy will be key to that success.

Evaluation of Bait Station Density for Oral Rabies Vaccination of Raccoons in Urban and Rural Habitats in Florida.

Efforts to eliminate the raccoon variant of the rabies virus (raccoon rabies) in the eastern United States by USDA, APHIS, Wildlife Services and cooperators have included the distribution of oral rabies vaccine baits from polyvinyl chloride (PVC) bait stations in west-central Florida from 2009 to 2015. Achieving sufficient vaccine bait uptake among urban raccoons is problematic, given limitations on aerial and vehicle-based bait distribution for safety and other reasons. One or three bait stations/km² were deployed across four 9-km² sites within rural and urban sites in Pasco and Pinellas Counties, Florida. Based on tetracycline biomarker analysis, bait uptake was only significantly different among the urban (Pinellas County) high and low bait station densities in 2012 (p = 0.0133). Significant differences in RVNA were found between the two bait station densities for both urban 2011 and 2012 samples (p = 0.0054 and p = 0.0031). Landscape differences in terms of urban structure and human population density may modify raccoon travel routes and behavior enough for these differences to emerge in highly urbanized Pinellas County, but not in rural Pasco County. The results suggest that, in urban settings, bait stations deployed at densities of >1/km² are likely to achieve higher seroprevalence as an index of population immunity critical to successful raccoon rabies control.