Molecular characterization of the rotavirus enterotoxin NSP4 gene of strains causing diarrhoea in children aged 0-5 years in northern India

Abstract

Non structural protein 4 (NSP4) gene of Rotavirus encodes a multifunctional protein which has significant role in viral multiplication and pathogenesis of acute watery diarrhoea associated with rotaviral gastroenteritis. It is known as the first viral enterotoxin and mutations of the gene have been linked to altered pathogenesis. This study was planned to ascertain the genotypes and genetic variations of NSP4 gene in the rotavirus strains prevalent in this area. We collected consecutive diarrhoeal stools from equal no of children aged under five years hospitalized with diarrhoea in a period from January 2010 to June 2012 and tested them for rotavirus antigen by ELISA. NSP4 gene was amplified by RT-PCR and subsequently sequenced (Big-Dye terminator kit using 3130 ABI, Genetic analyzer) and genotyped by Rotavirus C software. Of the 260 samples, 58(22.3%) samples were positive by ELISA. We were able to amplify NSP4 gene by RTPCR from 45 strains of which 35 amplicons were selected for sequencing. Total 25(71.4%) strains belonged to genotype E1, 6 (17.1%) strains to genotype E2 and 4 (11.4%) matched with the genotype E6. Sequence analysis revealed changes in the nucleotides causing punctate mutations in the conserved regions, the Inter species variable domain (ISVD) and the enterotoxin region (amino acid 114-135). On evolutionary analysis of 33 strains amino acid at position 131 was found under positive selection.