The safety and efficacy of immunizing foxes (Vulpes vulpes) using bait containing attenuated rabies virus vaccine.

Foxes given ERA rabies vaccine baits were challenged at one, six, 12 and 24 months later and showed a resistance to challenge in 80%, 78%, 60% and 44% of individuals respectively. All animals showing seroconversion following vaccination, resisted challenge at 24 months, suggesting that successful vaccination by the oral route could confer a relatively long term duration of immunity. The trials showed that fox pups did not immunize as easily as adult foxes using ERA rabies vaccine baits. Back-passage studies and the consumption of ERA injected mice by foxes failed to show any reversion of the vaccine virus to a virulent state. The fox and mouse are shown to be highly susceptible to rabies street virus, while the domestic species tested are consisderably more resistant. Monkeys were found to be intermediate in susceptibility to the virus. Safety tests carried out on various species of wildlife showed only the mouse to be susceptible to infection from ingesting the vaccine in the form of a bait. ERA rabies vaccine was shown to be safe in monkeys even when high titred virus was administered by the oral route.