Behaviour of an Attenuated Strain of Foot-and-mouth Disease Virus in Culture

Abstract

IN previous articles^1,2 it was reported that differences were found between virulent and attenuated strains of foot-and-mouth disease virus in surviving cultures of calf tongue epithelium. The attenuated strains (a) gave rise to a lower number of infective centres after adsorption, (b) were less efficiently titrated in the epithelial cultures, (c) multiplied to a lower titre, but (d) produced more interferon, and (e) were more sensitive to interferon action than the virulent strains. From the findings it was suggested that at the most only 5 per cent of the attenuated strain was competent, that is, was able to initiate infection and the further production of virus. The other 95 per cent was thought to enter the cell, inducing cellular resistance and the production of interferon. As a result of successive multiplication cycles of competent virus there was a build-up of non-competent virus and of interferon, which, in turn, inhibited the growth of competent virus. Hence there was a failure of lesion development in animals but still sufficient antigen production to stimulate immunity.