Genetic analysis of foot-and-mouth disease virus serotype A of Indian origin and detection of positive selection and recombination in leader protease- and capsid-coding regions.

The leader protease (Lpro) and capsid-coding sequences (P1) constitute approximately 3 kb of the foot-and-mouth disease virus (FMDV). We studied the phylogenetic relationship of 46 FMDV serotype A isolates of Indian origin collected during the period 1968–2005 and also eight vaccine strains using the neighbour-joining tree and Bayesian tree methods. The viruses were categorized under three major groups – Asian, Euro-South American and European. The Indian isolates formed a distinct genetic group among the Asian isolates. The Indian isolates were further classifi ed into different genetic subgroups (<5% divergence). Post-1995 isolates were divided into two subgroups while a few isolates which originated in the year 2005 from Andhra Pradesh formed a separate group. These isolates were closely related to the isolates of the 1970s. The FMDV isolates seem to undergo reverse mutation or convergent evolution wherein sequences identical to the ancestors are present in the isolates in circulation. The eight vaccine strains included in the study were not related to each other and belonged to different genetic groups. Recombination was detected in the Lpro region in one isolate (A IND 20/82) and in the VP1 coding 1D region in another isolate (A RAJ 21/96). Positive selection was identifi ed at aa positions 23 in the Lpro (P<0.05; 0.046*) and at aa 171 in the capsid protein VP1 (P<0.01; 0.003**).

Construction of an infectious cDNA clone of foot-and-mouth disease virus type O.

Foot-and-mouth disease virus (FMDV) serotype O is the most predominant among the endemic serotypes in India. A stable, full-length cDNA clone of FMDV type O 1 BFS 1860 preceded by a bacteriophage T7 polymerase promoter was assembled in a plasmid vector pGEMR-7Zf(–). An ~8.2 kb PCR product was amplifi ed from the cDNA clone and a full-length RNA was generated from it by in vitro transcription. Transfection of BHK-21 cells with the in vitro transcripts resulted in the production of infectious recombinant FMDV particles as evidenced by cytopathic effects (CPE). Further, characterization of the recombinant virus by immunofl uorescence, microneutralization test (MNT), antigen ELISA, RT-PCR, plaque assay and electron microscopy revealed similarity to the parental strain. The immunogenicity of an oil-adjuvant vaccine prepared using the inactivated recombinant virus was tested in guinea pigs and cattle. Neutralizing antibodies were produced in both vaccinated guinea pigs and cattle. Vaccinated animals were protected on challenge. The results demonstrated that the recombinant virus was as stable and effective as the parental strain for the preparation of inactivated vaccine, suggesting the potential application of this strategy to make genetically engineered FMDV vaccines.