Oral immunization against rabies with an avirulent mutant of the CVS strain: Evaluation of its efficacy in fox ( Vulpes vulpes) and its infectivity in seven other species

Abstract

Summary The results of oral vaccination trials performed on foxes with the AVO1 mutant strain of rabies virus selected with antiglycoprotein neutralizing monoclonal antibodies are reported. AVO1 was efficient when the vaccine was administered directly into the mouths of the animals. Vaccination led to the production of virusneutralizing antibodies in 7 out of 13 foxes and to the protection of 10 out of 13 after a challenge at day 90 when the titre of the vaccine exceeded 10 7 LD 50 for suckling mice. However, incorporation of the vaccine in baits (chicken heads) was not efficient. Innocuousness of AVO1 was tested in foxes and in 7 non-target species, including 6 species of rodents (a total of 247 animals). The virus could be isolated from the brains of two rodents of the genus Arvicola , but it was absent from the salivary glands of these animals. The stability of the AVO1 strain was poor because it easily reverted to a virulent phenotype after successive passages in the brains of suckling mice. Consequently, further studies should be carried out with the aim of improving the conditions of incorporation of the virus in the baits and of increasing the genetic stability of AVO1 before testing this mutant in the field.