[Transmissibility and pathogenicity in the red fox of two rabies viruses isolated at a 10 year interval]

Two rabies virus strains collected from naturally infected foxes in France in 1976 and 1986 were inoculated in 2 groups each consisting of 10 foxes (approximately 50 lethal doses50 mouse intracerebral per fox). Another 20 healthy foxes were kept in the same cages as the inoculated animals in order to study the transmission of both strains. All the inoculated foxes became rabid and transmitted rabies to their cage companion. The intervals between death of the inoculated foxes and death of the cage companion were significantly more variable (P less than 0.001) with the earlier strain, from 1 to 33 days compared to the range obtained with the later strain, 10-14 days. However, the mean intervals did not differ. Epidemiological consequences of such a decrease in variability, if confirmed in the field could decrease the epidemiological extent of rabies. Viremia was demonstrated in 2 foxes inoculated with the later strain but we cannot assume this to be a characteristic of this strain compared with the earlier strain. Rabies virus (both strains) was isolated from the saliva of foxes 29 days or less before the onset of clinical symptoms. This last result raises the question of the time limit as regards security before onset of clinical symptoms in animals involved in human contamination.