Genetic and antigenic analysis of type A foot-and-mouth disease viruses isolated in India during 1987-1996.

Twenty-three foot-and-mouth disease virus (FMDV) type A field isolates, recovered from different outbreaks during 1987-1996 in India, were subjected to antigenic and genetic analysis. The isolates showed a close antigenic relationship to the current vaccine strain (IND 17/77) in micro-neutralization test conducted using a vaccine strain (IND 17/77) antiserum and a peptide (aa 136-151 of VP1 protein of the A22/Azerbaijan/65 strain) antiserum. However, the isolates revealed minor antigenic differences in their reactivity with three neutralizing monoclonal antibodies (MAbs) recognizing trypsin-sensitive conformation-independent epitopes of the vaccine virus strains. Phylogenetic relationship between the isolates was carried out employing a part of the 1D gene (168 nucleotides at the 3'-end). Additional seven type A Indian field isolates reported earlier were included in the analysis. The percent similarity among the Indian isolates varied from 82.7% to 99.4% at nucleotide level, and from 83.9% to 100% at amino acid level. These observations clearly demonstrate genetic heterogeneity of the field isolates. The current vaccine strain IND 17/77 showed divergence of 9.7% at nucleotide level and 5.6% at amino acid level from the A22 Iraq 24/64 isolate. The field strains were divergent from the vaccine strain IND 17/77 by 5.6%-14.6% and 3.7% 13.7% at nucleotide and amino acid level, respectively. In the phylogenetic tree, the isolates were distributed into 21 genetic groups. The clustering pattern of the isolates in the phylogenetic tree revealed no specific distribution pattern of the foot-and-mouth disease (FMD) outbreaks in relation to their geographical locations, caused by unrestricted animal movement and endemic nature of the disease.