Molecular Diagnosis of Porcine Reproductive and Respiratory Syndrome Outbreaks in Pigs of Mizoram State

Abstract

Background: Porcine reproductive and respiratory syndrome (PRRS) is considered as 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 (OIE) on the 26 June, 2013. Although the disease appeared to be contained in the Mizoram state, several severe outbreaks of the disease has been reported in subsequent years. The present study has determined the current status of porcine reproductive and respiratory syndrome in the pig population of Mizoram state and its diagnosis by molecular and immunohistochemistry technique. Methods: A total number of 365 pigs of different age groups from 5 organized and 35 backyard farms located in different districts of Mizoram were studied. A detailed necropsy was conducted on 88 dead pigs. Gross lesions were recorded and representative tissue samples were collected for histopatholgical, immunohistochemical studies and preserved at -80°C for molecular diagnosis. Result: Respiratory signs characterized by difficulty in breathing accompanied with high fever were the clinical signs observed in affected pigs. Severe haemorrhages in lungs with interstitial pneumonia, haemorrhagic lymphadenitis with lymphoid depletion in lymphoid organs were the most commonly observed lesions followed by haemorrhagic myocarditis and nephritis. Reverse transcription PCR targeting 300 bp fragments of ORF7 gene and real-time PCR targeting 152 bp fragments of ORF7 gene of PRRSV from the tissue extracted RNA (lung, lymph node, spleen) confirmed the outbreaks of PRRSV in different backyard and organized swine herds. The PRRSV antigen was demonstrated by immunohistochemistry in alveolar macrophages in lungs and infiltrating macrophages in spleen and lymph nodes tissues respectively.