Genomic characterization of coxsackievirus type B3 strains associated with acute flaccid paralysis in south-western India

Acute flaccid paralysis (AFP) associated with coxsackievirus type B3 (CV-B3) of the species Enterovirus B is an emerging concern worldwide. Although CV-B3-associated AFP in India has been demonstrated previously, the genomic characterization of these strains is unreported. Here, CV-B3 strains detected on the basis of the partial VP1 gene in 10 AFP cases and five asymptomatic contacts identified from different regions of south-western India during 2009-2010 through the Polio Surveillance Project were considered for complete genome sequencing and characterization. Phylogenetic analysis of complete VP1 gene sequences of global CV-B3 strains classified Indian CV-B3 strains into genogroup GVI, along with strains from Uzbekistan and Bangladesh, and into a new genogroup, GVII. Genomic divergence between genogroups of the study strains was 14.4 % with significantly lower divergence (1.8 %) within GVI (n = 12) than that within GVII (8.5 %) (n = 3). The strains from both AFP cases and asymptomatic contacts, identified mainly in coastal Karnataka and Kerala, belonged to the dominant genogroup GVI, while the GVII strains were recovered from AFP cases in north interior Karnataka. All study strains carried inter-genotypic recombination with the structural region similar to reference CV-B3 strains, and 5' non-coding regions and non-structural regions closer to other enterovirus B types. Domain II structures of 5' non-coding regions, described to modulate virus replication, were predicted to have varied structural folds in the two genogroups and were attributed to differing recombination patterns. The results indicate two distinct genomic compositions of CV-B3 strains circulating in India and suggest the need for concurrent analysis of viral and host factors to further understand the varied manifestations of their infections.