FIRST NORTH-AMERICAN FIELD RELEASE OF A VACCINIA-RABIES GLYCOPROTEIN RECOMBINANT VIRUS

Following nearly 10 yr of extensive laboratory evaluation, a vaccinia- rabies glycoprotein (V-RG) vaccine was the first recombinant virus to undergo limited North American field release on 20 August 1990. The fr ee-ranging raccoon population on Parramore Island (Virginia,, USA) was exposed to a high density (10 baits/ha) of vaccine-laden baits distri buted on a 300 ha vaccination area. Art annual total of 887 raccoons w ere live-trapped for sedation, physical examination and blood collecti on for rabies antibody determination: there was no evidence of adverse effects or lesions due to the vaccine. Age and sex distributions, mea n body weights, and live-capture histories of raccoons from the vaccin ation and non-baited control areas were compared. There were no statis tically significant differences in survivorship between the baited and nonbaited areas, nor between rabies antibody-positive and antibody-ne gative raccoons from the vaccination area. There was no trend in field mortality that suggested an association with either tetracycline or s ulfadimethoxine, used as biomakers, or with vaccine contact determined by antibody status. No gross or histopathologic lesions due to the va ccine were demonstrated among a subsample of live-trapped raccoons col lected for gross necropsy, biomarker analysis, histopathologic examina tion, and V-RG virus isolation attempts. Recovery of V-RG virus was li mited to the tonsils of two biomarker-postitive, clinically healthy ra ccoons collected from the vaccination area for postmortem examination on days 2 and 4 following bait distribution. These data reinforce the extensive body of safety data on the V-RG virus and extend it to inclu de field evaluation where vaccine is offered free-choice in abundance, in baits designed to attract free-ranging raccoons, in a relatively s imple ecosystem.