Kinetics of humoral immune response after rabies VR-G oral vaccination of captive fox cubs (Vulpes vulpes) with or without maternally derived antibodies against the vaccine.

In western Europe during the spring, the largest proportion of fox populations are cubs and the key to successful rabies oral vaccination campaigns is cub vaccination. In this paper we report on studies of the serology of 93 fox (Vulpes vulpes) cubs born to unvaccinated and orally vaccinated captive vixens, some of which were orally vaccinated at 30 or at 90 days of age with the vaccinia recombinant vaccine (VR-G) that expresses the rabies virus glycoprotein. The duration of cub passively acquired antibody, the development of immune responses to oral vaccination at either 30 or 90 days of age, possible interference between passive and active immunity to such vaccination and resistance to a potentially lethal rabies challenge dose when five months old were measured. The study showed that rabies neutralising antibody can be passed to their cubs by vixens orally vaccinated with VR-G during pregnancy. Maternally derived antibody titres in cubs declined with time and disappeared by 45-75 days after birth. Thirty days old cubs serologically responded to oral vaccination. No interference between antibody of maternal origin and active immunity conferred by VR-G oral vaccination or between antibody of maternal origin and protection was observed. Thus, very young cub immunisation against rabies with VR-G per os is possible whatever the immune status of their mothers. Provided a vaccine-bait suitable for such young cubs exists, oral vaccination at den entrances with VR-G is a feasibility.