Exposure Time of Oral Rabies Vaccine Baits Relative to Baiting Density and Raccoon Population Density

Abstract

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~nunity are few. We used the 22-km2 US National Aeror~autics 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 November 2002 we surveyed raccoon use of PBS along 19.3 km of paved-road transects by using a forward-looking infrared camera rnol~r~ted inside a vehicle. We used Distance 3.5 software to calc~~late a probaljility of detection function by whit11 we estimated raccoon pop~ilation density from transect data. Estimated population density on PBS decreased from August (33.4 raccoons/km2) through November (13.6 raccoons/krn2), yielding a monthly rnean of 24.5 raccoons/km2. We also quantified exposure time for ORV baits placed by hand on five 1-km2 grids on PBS from September 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 assllming 22.9% nontarget take, the baiting density of 75/ km' yielded an average of 3.3 baits consurned per raccoon anti the sachet perforated.

Oral Vaccination Against Raccoon Rabies: Landscape Heterogeneity and Timing of Distribution Influence Wildlife Contact Rates With the Onrab Vaccine Bait

“…The overall contact rate with vaccine baits after 7 days in this study was lower than what has been found in similar studies in the United States with the V-RG or alternative baits (Hadidian et al, 1989;Hable et al, 1992;Hanlon et al, 1998;Blackwell et al, 2004). This discrepancy may be explained by differences among study areas in density of raccoons and potentially other species attracted to the bait, as well as the time when these studies were conducted.…”

“…This discrepancy may be explained by differences among study areas in density of raccoons and potentially other species attracted to the bait, as well as the time when these studies were conducted. For instance, Blackwell et al (2004) estimated a mean density of 24.5 raccoons/km 2 in their study area, whereas the density near our study site has been estimated at 13 raccoons/km 2 (Monté ré gie, Qué bec, Canada; Jolicoeur et al, 2009). Differences in animal density can, therefore, partly account for the higher rate of disappearance of the V-RG baits in previous studies.…”

“…However, given that the ONRAB bait is new, no information has been made available on the species that are attracted to this bait in the wild nor at what rate the baits are consumed after distribution. Previous field studies on the V-RG and other types of vaccine baits, have shown that the rate of disappearance of baits can sometimes be as high as 90% a week after their distribution (Hadidian et al, 1989;Hable et al, 1992;Hanlon et al, 1998;Olson and Werner, 1999;Blackwell et al, 2004). Our goals were to evaluate whether ONRAB baits are consumed at a similar rate under natural conditions and to investigate whether targeted species (raccoons and skunks) and nontargeted species were attracted to this alternative to the V-RG bait.…”

Lipid-Formulated BCG as an Oral-Bait Vaccine for Tuberculosis: Vaccine Stability, Efficacy, and Palatability to Brushtail Possums (Trichosurus Vulpecula) in New Zealand

“…Most commonly for oral wildlife vaccines, the vaccine itself is delivered inside a separate bait, as is the case with existing rabies and classical swine fever wildlife vaccines (Kaden et al, 2003;Blackwell et al, 2004), as well as prototypical vaccines for plague (Creekmore et al, 2002). In the present study we have evaluated the novel FIGURE 3.…”

“…When applied at a density of 35 baits/ha, 85% of recaptured possums had indications of bait uptake; this figure was increased to 100% uptake by doubling the baiting density. Both of these baiting densities are markedly higher than those used in wildlife vaccine delivery programs for either mesocarnivores or porcines (Rosatte and Lawson, 2001;Blackwell et al, 2004;Campbell et al, 2006); however, it must be appreciated that possums reach much higher population densities in New Zealand bush because of their utilization of a tree canopy habitat and their monopolization of the browsing niche, thus requiring a higher baiting density. There are estimated to be over 70 million possums in New Zealand, with population densities over 2,000 animals per km 2 reported in favorable broadleaf forest habitats (Efford, 2000).…”