Intradermal inoculation of the tongue, subcutaneous, intracutaneous and intra-venous inoculation were compared in determining the relative facility with which foot-and-mouth disease infection can be produced in cattle.
In seven experiments using six virus strains, least virus was required to infect by the intradermal tongue route, but wide variation was observed between the amount of virus required to infect by this route and by the subcutaneous, intracutaneous or intravenous routes. The smallest difference between tongue and subcutaneous inoculation was not significant, and the largest difference was that 250,000 times more virus was required to infect by the subcutaneous route. The readiness with which infection is produced by routes other than intradermal inoculation of the tongue may be greatly influenced by the strain of virus used.
Intranasal instillation of the virus was also compared with intradermal tongue inoculation. As with subcutaneous inoculation, more virus was required for infection by the intranasal route and, similarly, the results suggest that considerable variation would be found in the amount of different strains required.
A correlation is suggested between this variation and the variation observed in the ‘invasiveness’ of strains in cattle exposed to contact infection.
Attention is drawn to the significance of the observations recorded in this paper in relation to tests of foot-and-mouth disease vaccines for non-infectivity.