PREVENTION OF THE SPREAD OF RABIES TO WILDLIFE BY ORAL VACCINATION OFRACCOONS IN MASSACHUSETTS

Objective-To evaluate the use of bait containing rabies vaccine to cre ate a barrier of rabies-vaccinated raccoons in Massachusetts and to de termine the effectiveness of various bait distribution strategies in h alting the spread of rabies. Design-Prospective study. Sample Populati on-Free-ranging raccoons. Procedure-Baits were distributed twice yearl y in a 207-km(2) (80-mi(2)) area in the vicinity of the Cape Cod Canal . Bait density and distribution strategy varied among 3 treatment area s. Raccoons were caught in live traps after bait distribution and anes thetized; blood samples were obtained to measure serum antibody liters to rabies virus. Vaccination rates were determined by the percentage of captured raccoons with antibody titers to rabies virus greater than or equal to 1.5. In addition, raccoons with clinical signs of illness inside the vaccination zone and adjacent areas were euthanatized and submitted for rabies testing. Results-The percentage of vaccinated rac coons differed significantly among the following 3 areas with various bait densities: high-density area with uniform bait distribution (103 bails/km(2) [267 baits/mi(2)]) = 37%; low-density area with additional targeted bait distribution (93 bails/km(2) [240 baits/mi(2)]) = 67%; and, high-density area with additional targeted bait distribution (135 baits/km(2) [350 baits/mi(2)]) = 77%. Nineteen animals with rabies (1 5 raccoons, 3 skunks, 1 cat) were reported in the area just outside of the vaccination zone, but only 1 raccoon with rabies was reported fro m inside the vaccination zone. Clinical Implications-In this suburban study area, an approximate vaccination rate of 63% was sufficient to h alt the spread of rabies in free-ranging raccoons. Compared with unifo rm bait distribution, targeting raccoon habitats increased vaccination rates.