The development and use of a vaccinia-rabies recombinant oral vaccine for the control of wildlife rabies; a link between Jenner and Pasteur

Abstract

To improve both safety and stability of the oral vaccines used in the field to vaccinate foxes against rabies, a recombinant vaccinia virus, which expresses the immunizing G protein of rabies virus has been developed by inserting the cDNA which codes for the immunogenic glycoprotein of rabies virus into the thymidine kinase (TK) gene of the Copenhagen strain of vaccinia virus. The efficacy of this vaccine was tested by the oral route, primarily in foxes. The immunity conferred, a minimum of 12 months in cubs and 18 months in adult animals, corresponds to the duration of the protection required for vaccination of foxes in the field. Innocuity was tested in foxes, domestic animals, and in numerous European wild animal species that could compete with the red fox for the vaccine bait. No clinical signs or lesions were observed in any of the vaccinated animals during a minimum of 28 days post vaccination. Moreover, no transmission of immunizing doses of the recombinant occurred between foxes or other species tested. To study the stability of the vaccine strain, baits containing the vaccine were placed in the field. Despite considerable variations of environmental temperatures, the vaccine remained stable for at least one month. Because bait is taken within one month, it can be assumed that most animals taking the baits are effectively vaccinated. To test the field efficacy of the recombinant vaccine, large-scale campaigns of fox vaccination were set up in a 2200 km2 region of southern Belgium, were rabies was prevalent. A dramatic decrease in the incidence of rabies was noted after the campaigns. The recombinant is presently used to control wildlife rabies in the field both in several European countries and in the United States.