Emergence of a novel lineage genetically divergent from the predominant Ind2001 lineage of serotype O foot-and-mouth disease virus in India.

In India, emergence of Ind2001 lineage of foot-and-mouth disease virus (FMDV) serotype O was recorded in the year 2001. After causing sporadic incidences, the Ind2001 lineage that re-surged in 2008 out-competed PanAsia from the field during 2009 and continued its dominance during 2010 and 2011 as well. The lineage has diversified in due course of time, leading to two sub-lineages (Ind2001a and Ind2001b). The sub-lineage Ind2001a include isolates collected during 2001-2002 and sub-lineage Ind2001b is constituted largely by isolates collected during 2008-2012. The nucleotide substitution rate of sub-lineage Ind2001b was estimated at 6.58×10⁻³ substitutions/site/year. The most stable PanAsia lineage is restricted only to few outbreaks. During 2011, emergence of a new genetic group with >9% nucleotide divergence from rest of the lineages circulating in the country was detected and named as lineage Ind2011. Two specific amino acid substitutions at positions VP1-36 (F) and VP2-133 (T) were observed in the Ind2011 lineage. The new lineage at present is restricted only to southern states of the country. It is uncertain whether the emergence was triggered by immune pressure or due to a bottleneck in transmission or selected for higher fitness value. Six sites (4, 68, 83, 135, 138 and 209) in VP1 protein were identified to undergo episodic diversifying selection in serotype O field isolates. Both emerging and re-emerging lineages had appropriate antigenic match with currently used vaccine strain, INDR2/1975. Irrespective of genetic variability, the field isolates showed remarkable conservation at antigenically critical residues that might contribute to the observed antigenic stability. With the emergence of a new genetic group after a span of 10 years, the overall epidemiological scenario in the region is expected to change in the coming years.

Immunodiagnosis of foot-and-mouth disease using mutated recombinant 3ABC polyprotein in a competitive ELISA.

Differentiation of infected from vaccinated animals (DIVA) is essential for effective control of foot-and-mouth disease (FMD) by vaccination. The antibody response against FMD viral non-structural proteins (NSPs) has been used widely for this purpose. Among all the NSPs, the 3ABC polyprotein has been recognized as the most appropriate indicator for DIVA. In this study, mutated full-length 3ABC polyprotein was expressed in a prokaryotic system and monoclonal antibody against the recombinant protein was developed. A competitive ELISA (C-ELISA) for DIVA was standardized for different species of livestock animals using recombinant 3ABC and monoclonal antibodies. The diagnostic sensitivity and specificity of the assay were estimated by testing a panel of known serum samples consisting of sera from naive, vaccinated and infected animals as 86.9% with 66.4-97.2 (95%) confidence interval and 97% with 89.6-99.6 (95%) confidence interval respectively at 40% inhibition cut-off. The assay was validated further by testing sera from different livestock species collected at random from different parts of the country. The assay will provide a common method for testing sera from different species of livestock and wild animals. The C-ELISA is a sensitive and specific DIVA assay for FMD and can be used as a method for FMD control programme with vaccination.