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Methods and Strategies for Controlling Rabies

Project Accomplishments 2018-2019

PROJECT GOAL: To serve the National Rabies Management Program and aid in the control of rabies through the conduct of research that aids in the overall understanding of rabies and helps the Program optimize management by the development of better strategies, methods and tools for controlling infection and spread in wildlife for the benefit of humans, livestock and wildlife.

Rabies is an acute, fatal viral disease most often transmitted through the bite of a rabid mammal. It can infect people as well as animals and has far-reaching impacts on society. In the United States, rabies virus circulation is maintained by various wildlife, including bats, raccoons, skunks, gray foxes, arctic foxes, and mongooses. In an effort to halt the spread and eventually eliminate specific wild carnivore variants of rabies virus in the United States, National Wildlife Research Center (NWRC) scientists conduct research on the behavior, ecology, movements, and population structure of wildlife reservoirs. These scientists also evaluate methods and techniques to orally vaccinate free-ranging wildlife against rabies to achieve management objectives of control and elimination. 

Biomarkers for Use with Mongoose Oral Rabies Vaccine. The small Indian mongoose (Herpestes auropunctatus) is a reservoir of rabies virus in Puerto Rico and comprises over 70 percent of animal rabies cases reported annually. Oral rabies vaccination (ORV) is the primary strategy used to control rabies in wildlife reservoirs, but currently no wildlife ORV program exists in Puerto Rico. Research into oral rabies vaccines and optimal bait types for mongooses has been done in Puerto Rico with promising results. To help evaluate ORV strategies targeting free-ranging mongooses in Puerto Rico, NWRC researchers tested the effectiveness of two biomarkers (ethyl-iophenoxic acid and methyl-iophenoxic acid) incorporated into placebo ORV baits to estimate bait uptake by captive mongooses. A biomarker is a measurable substance in an animal that can indicate that it has at least partially eaten a bait. Researchers fed biomarker-treated baits to mongooses and collected blood samples from mongooses prior to treatment, one day post-treatment, and then weekly up to 8 weeks post-treatment. Results showed that mongooses which consumed greater than or equal to 25% of the marked baits demonstrated robust short and long-term (4 to 8 weeks) levels of iophenoxic acid biomarker in their sera, which will be useful in evaluating future ORV programs for mongooses on Puerto Rico.

Evaluating Rabies Surveillance Strategies and Determining Rabies Elimination. The National Rabies Management Program (NRMP) is working to eliminate the raccoon variant of rabies virus from the eastern coast of the United States. NWRC researchers are collaborating with the NRMP to determine when raccoon rabies has been eliminated from an area. This information helps inform strategic movements of the Oral Rabies Vaccination (ORV) management zone. Additionally, NWRC researchers are evaluating the effectiveness of different surveillance strategies to help ensure the efficient allocation of surveillance resources. This collaborative approach helped inform ORV zone placement in Ohio, West Virginia, and Pennsylvania. It also contributed to FY19 management decisions in New York, Vermont, and New Hampshire to move the ORV zone 20 miles south of the Quebec border as part efforts to eliminate raccoon rabies in northeastern U.S and Canada.  

Efficacy of Ontario Rabies Vaccine Bait (ONRAB) for Raccoons. The RABORAL V-RG product is the only oral rabies vaccine currently permitted for use with free-ranging raccoons and coyotes in the United States. However, another product— the Ontario Rabies Vaccine Bait (ONRAB) —has shown promise for controlling rabies in raccoons and striped skunks in Canada. NWRC researchers evaluated the efficacy of ONRAB for raccoons in the United States. Fifty captive raccoons were given either sham or live vaccine baits and then challenged with a lethal dose of rabies virus. All sham-vaccinated raccoons succumbed to rabies, while only 15 percent of the ONRAB-vaccinated raccoons developed rabies. The results compliment recent field data showing the potential of ONRAB for the control and prevention of rabies in free-ranging raccoon populations. During 2012-2014, NWRC researchers and the WS National Rabies Management Program distributed ONRAB baits in areas of New York, Vermont and New Hampshire. Seroprevalence of rabies virus neutralizing antibodies in sera from the raccoon population was 27.3% prior to the trial and averaged 68.5% post-baiting across the three years study, respectively. The captive trial and field data were shared with the USDA Center for Veterinary Biologics (CVB) as part of a comprehensive package submitted by the vaccine company for consideration towards permitting ONRAB for broader use in the United States.

Oral Rabies Vaccine Bait Flavors for Skunks. Wildlife are the leading cause of rabies infections in animals and people in the United States. While the number of human deaths due to rabies is low in the U.S., one study has estimated that over 20,000 people are exposed and receive post-exposure vaccination each year. To eliminate and prevent rabies virus circulation in wild carnivores, the WS’ National Rabies Management Program distributes millions of oral rabies vaccine baits each year, and most of these baits target raccoons in the eastern United States. Skunks are also an important spillover recipient of raccoon rabies. Because of this, effective oral rabies vaccine products are also needed for skunks. In a recent study, NWRC researchers tested the preference of skunks for six different flavors of placebo Ontario Rabies Vaccine Bait (ONRAB), a product which is permitted in Canada for use with skunks. They also tested the dose of vaccine required to protect the skunks against rabies infection, to evaluate whether reductions in vaccine volume and dose may be feasible without compromising efficacy. Results showed chicken, cheese, and egg flavors were preferred over the plain flavor, but strong flavor preferences were not observed among captive skunks. Also, a relatively high dose of vaccine was needed to protect skunks against rabies. The findings aid in further refinement of ONRAB baits for delivery to skunks in the United States.

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