Pathogenic characterization of porcine reproductive and respiratory syndrome virus of Indian origin in experimentally infected piglets.

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is an economically importanttransboundary viral disease of pigs confronting the swine industry worldwide. Thisstudy was aimed to assess the pathogenic potential of PRRS virus belonging togenotype 2 that emerged in India in 2013. Nine 6-week-old piglets were inoculatedintranasally with 29105.75TCID50/ml of PRRSV (Ind-297221/2013). Three pigletswere kept as uninfected controls. Blood and nasal swabs were collected daily up to7 days post-infection (dpi) and on alternate days subsequently. Piglets were necrop-sied for tissue sample collection either on death or after euthanasia on 7, 14 or21 dpi (one uninfected control and three PRRSV-infected piglets per interval). Thevirus caused high fever, typical blue ear, weight loss, respiratory distress, diarrhoeaand leucopenia between 2 and 8 dpi. Two infected piglets died (on 3 and 17 dpi)during the course of study. The presence of virus in serum and nasal secretion wasobserved up to 19 and 17 dpi, respectively, with the maximum load between 4 and7 dpi. Seroconversion started 6 dpi and the mean PRRSV antibody titre reached upto 640 by 21 dpi. Virus load was highest in tonsils at all the intervals, whereas inspleen and lymph nodes load was higher in later intervals. Major microscopic lesionsin PRRSV-infected piglets included moderate to severe interstitial pneumonia, lym-phoid depletion in tonsils and lymph nodes (cystic), thymic atrophy, reactive hyper-plasia followed by lymphoid depletion in spleen. PRRSV antigen was consistentlydemonstrated by immunoperoxidase test in the lungs, spleen, tonsils and lymphnodes. Antigen distribution was more widespread on 7 and 14 dpi than on 21 dpi.The findings establish that the Indian PRRSV is highly pathogenic to piglets.