Phylogenetic structure of serotype A foot-and-mouth disease virus: global diversity and the Indian perspective.

Global epidemiological analysis is vital for implementing progressive regional foot-and-mouth disease control programmes. Here, we have generated VP1 region sequences for 55 Indian type A outbreak strains and have included complete VP1 sequences from 46 other countries to obtain a comprehensive global phylogeographical impression. A total of 26 regional genotypes within three continental topotypes, based on a 15% nucleotide divergence cut-off criterion, could be identified. These genotypes correlated with distinct evolutionary lineages in the maximum-likelihood phylogeny. During the last decade, ten genotypes have been in circulation the world over and it was evident that no type A strain has transgressed the continental barriers during this period. A single genotype (genotype 18) within the Asia topotype has been circulating in India with neither any incursion nor any long distance movement of virus out of the country during the last ten years, although close genetic and epidemiological links between viruses from Bhutan and India were revealed.

Emergence of antigenic variants with in serotype A foot and mouth disease virus in India and evaluation of a new vaccine candidate panel.

Emergence of genetically and antigenically divergent lineages/genotypes and poor intergenotypic antigenic coverage is a major concern in serotype A foot-and-mouth-disease virus (FMDV) in India. In 2009, to cover antigenic diversity emerged in serotype A virus field isolates, IND40/2000 was selected as the new vaccine strain for incorporation in the trivalent FMD vaccine formulation used in India. Although current vaccine strain (IND40/2000) covers most isolates antigenically, a few VP3(59)-deletion group isolates showed low r-value in routine vaccine matching exercise. The VP3(59)-deletion group within genotype 18 emerged first in late part of 2002 and in 2007 causing outbreaks along with non-deletion isolates of the same genotype. In case of emergence or re-emergence of more antigenically divergent isolates in future, a need for a new vaccine candidate to cover maximum isolates of both deletion and non-deletion group may arise. Four alternate candidate vaccine strains (IND281/2003, IND195/2007, IND360/2007 and IND123/2008) were selected based on set criteria and antigenic relationships with field isolates sampled between 2002 and 2009 were analyzed using a micro-neutralization test. Phylogenetic analysis based on capsid region of serotype A isolates revealed existence of two broad distinct clusters (VP3(59)-deletion and non-deletion group) within genotype 18. The VP3(59)-deletion group has diversified genetically with time giving rise to three different sub-lineages (clade18a, 18b and 18c). The present study indicates that the virus candidates IND281/2003 (VP3(59)-deletion group) and IND195/2007 (non-deletion group) can be used as an adjunct or alternative strain to currently used vaccine strain IND40/2000 in case of emergence of more antigenically divergent isolates in future.