ABSTRACT
Since its first outbreak in 2013, porcine reproductive and respiratory syndrome (PRRS) has established as an enzootic disease in pig population of Mizoram state, India. Our previous studies based on phylogenetic analysis of ORF5 and ORF7 gene sequences revealed close relationship of Indian PRRSV with the highly pathogenic variant of PRRSV (HP-PRRSV) of Chinese origin. Despite the control measures, second major outbreak of the disease was recorded in Aizawl district of Mizoram in 2015. The objective of the present study was to examine the origin of PRRSV isolates of 2015 outbreak, identification of deleted region in Nsp2 gene and determination of any genetic variation between 2013 and 2015 isolates of PRRSV. The outbreak was confirmed by the detection of PRRSV-specific antibodies in 57 out of 92 serum samples (61.96 %) and also by RT-PCR in 42 out of 42 necropsy samples (100 %). Nucleotide sequence analysis of Nsp2 coding region of Indian isolates and comparison with reference sequences revealed 90 nucleotides discontinuous deletion further establishes the closeness of Indian PRRSV to Chinese HP-PRRSV. Further, sequence and phylogenetic analysis of ORF5, ORF7 and Nsp2 genes of Indian PRRSV from both 2013 and 2015 revealed that the outbreaks were caused by two different strains of HP-PRRSV closely associated with the Chinese 10 HEB-3 isolate and 07QN isolates of Vietnam origin respectively. The present study confirms that the Indian PRRSV is a highly pathogenic variant of PRRSV and this study serves as the basis for developing practical and effective control measures against this disease.
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.
