Clinical signs and symptoms, gross and histopathological lesions of porcine reproductive and respiratory syndrome (PRRS) in naive and naturally infected pigs of Mizoram : A detailed study

The clinical manifestations and pathological lesions of Porcine Reproductive and Respiratory Syndrome (PRRS) infection in naturally infected pig population was studied in the present study. Affected pigs exhibited anorexia, lethargy, pyrexia, dyspnoea, and cyanosis of extremities. In sows, reproductive failure characterized by stillbirths, mummifications, delivery of weak born piglets and high pre-weaning mortality were recorded. Pigs died of PRRS revealed severe gross changes in lungs and lymphoid organs including spleen and tonsils. Affected lungs were non collapsible, enlarged, edematous with diffused areas of hemorrhages and rib imprints on its surface. Microscopical examination revealed severe interstitial pneumonia characterized by thickening of alveolar wall due to mononuclear cell infiltration, along with profound congestion and hemorrhages. Swelling, congestion and hemorrhages were consistently observed in lymph nodes particularly inguinal, mesenteric, and bronchial lymph nodes. Microscopically severe lymphoid depletion leading to cavity formation in the germinal centers was observed. Spleen in all the affected animals appeared swollen with areas of infarction and congestion, and showed lymphoid depletion with diffuse parenchymal hemorrhages. The kidneys appeared swollen and revealed severe interstitial and glomerulo nephritis. Confirmatory diagnosis of PRRS was done using reverse transcriptase-polymerase chain reaction (RT-PCR) to detect the ORF7 gene of PRRSV in tissue lesions.