Project Directorate on Foot-and-Mouth Disease, Indian Veterinary Research Institute Campus, Mukteswar-Kumaon, Nainital-263138, Uttarakhand, India.
Previous studies on 1D/VP1 gene based phylogeny indicates that Indian type Asia1 field isolates could be grouped in to two distinct genetic lineages, B and C. Of the two, lineage C was found to be circulating commonly since 1998 and was behind majority of the outbreaks due to type Asia1 in India. The isolates of lineage C could be subdivided in to two distinct sub clusters, CI and CII with more than 10% nucleotide sequence divergence. The isolates of lineage CII emerged late in 2001 and dominated the period between 2002 and 2004. The lineage CI dominated the Asia1 field outbreak between 1998 and 2002, although disappeared between year 2001 and 2004 again emerged as the predominating lineage from 2005 onwards. Phylogenetic analysis of Asia 1 isolates of 2005–07 from different states indicates that they all belong to lineage CI baring only one isolate IND113/06 which grouped with lineage CII. This implies continuous emergence and reemergence of lineages as part of evolutionary process and a similar occurrence was perceived previously with type O viruses in our country. This is in contrast to type A where it seems that, as the new sub-genotypes appear the old ones disappear, a phenomenon that has been termed as lineage turnover. Although the field isolates of Asia1 showed considerable genetic variation among themselves, all of them were serologically related to in-use vaccine strain. No correlation could be made between geographical origin of the isolates and their clustering pattern in the phylogenetic tree which implies constant movement of the animals across the country.
