Date of this Version
Oral rabies vaccination (ORV) baiting programs for control of raccoon (Procyorl lotor) rabies in the USA have been conducted or are in progress in eight states east of the Mississippi River. However, data specific to the relationship between raccoon population density and the minimum density of baits necessary to significantly elevate rabies im~nunitya re few. We used the 22-km2 US National Aerorlautics and Space Administration Plum Brook Station (PBS) in Erie County, Ohio, USA, to evaluate the period of exposure for placebo vaccine baits placed at a density of 75 baits/km2 relative to raccoon population density. Our objectives were to 1) estimate raccoon population density within the fragmented forest, old-field, and industrial landscape at PBS; and 2) quantify the time that placebo, Merial HABORAL V-RG" vaccine baits were available to raccoons. Froin August through Nove~nber 2002 we surveyed raccoon use of PBS along 19.3 km of paved-road transects by using a forward-looking infrared carnera molrnted inside a vehicle. We used Distance 3.5 software to calc~ilate a proba1,ility of detection filnction by which we estimated raccoon pop~llation density from transect data. Estimated population density on PBS decreased from August (33.4 raccoons/krn2) through November (13.6 raccoons/krn2). yielding a nionthly mean of 24.5 raccoons/km2. We also quantified exposure tirne for ORV baits placed by hand on five 1-krn2 grids on PBS from Septelnber through October. An average 82.7% (SD=4.6) of baits were removed within 1 wk of placement. Given raccoon population density, estimates of bait removal and sachet condition, and assliming 22.9% nontarget take, the baiting density of 75/ km' yielded an average of 3.3 baits consurned per raccoon anti the sachet perforated. k y words: Bait density, forward-looking infrared carnera, oral vaccination, population density, rabies. raccoon.