Porcine reproductive and respiratory syndrome virus (PRRSV) from the first outbreak of India shows close relationship with the highly pathogenic variant of China

Abstract

Background: Porcine reproductive and respiratory syndrome (PRRS) is an economically important viral disease of pigs worldwide. India has reported the first outbreak of PRRS in the pig population of Mizoram state to the Office International des Epizooties on the 26 June 2013.

Hypothesis/objectives: The aim of the present study was to determine the genotype and origin of porcine reproductive and respiratory syndrome virus (PRRSV) from the first outbreak in the pig population of Mizoram state, India, in 2013.

Animals and methods: A total of 880 affected pigs from the outbreak were clinically examined, 51 animals were necropsied and tested by reverse transcription polymerase chain reaction (RT-PCR) to detect PRRSV and 148 serum samples were tested to detect PRRSV-specific antibodies. The full open reading frame 5 (ORF5) gene sequences from 12 and ORF7 gene sequences from three clinical cases were sequenced and analysed for genomic characterization, respectively.

Results: The outbreak was confirmed by the detection of PRRSV-specific antibodies in 109 out of 148 serum samples (74%) and also by RT-PCR in 46 out of 51 necropsy samples (90%). Notably, ORF5 and ORF7 genes of Indian strain shares the same nucleotide positions i.e. 13,698-14,300 and 14,799-15,170, respectively, with the highly pathogenic (HP) strain of China and were grouped together in a phylogenetic tree.

Conclusions and clinical importance: Sequence and phylogenetic analysis of ORF5 and ORF7 confirmed that the Indian strain has a close link with the HP-PRRSV of China. The current study forms an essential step for better understanding of the epidemiology as well as the movement and spread of the disease in India.

Keywords: India; ORF5; ORF7; PRRS; phylogeny; pig; porcine.