Dual infection between a Thai isolate highly pathogenic porcine reproductive and respiratory syndrome virus and pandemic H1N1swine influenza virus in weanling pigs

Abstract

After an introduction of pandemic H1N1 swine influenza virus (pdmH1N1 SIV) in the Thai swine farms, mild clinical outcome is observed and its role in porcine respiratory disease complex (PRDC) is questionable. A highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has become endemic in the Thai swine farms. This study was conducted to determine the pathogenicity of the pdmH1N1 SIV when co-infected with a HP-PRRSV. Thirty-two weanling pigs from a free PRRSV, SIV, porcine circovirus type 2 (PCV-2) and Mycoplasma spp. commercial farm were randomly divided into 4 groups: Negative, PRRSV, SIV and Co-infection groups. Pigs in PRRSV and Co-infection groups were challenged intranasally with the Thai isolate HP-PRRSV at 0 days post HP-PRRSV challenge (dphc) and pigs in SIV and Co-infection groups were inoculated intratracheally with pdmH1N1 SIV at 6 dphc. The 1st and 2nd necropsies were done at 2 and 4 days post SIV challenge (dsc). A comparison of the lung lesion scores between PRRSV and Co-infection groups at 2 dsc showed no statistical difference, but at 4 dsc, lung lesions score of the Co-infection group had higher average score than that of the PRRSV only group. Also, SIV viral load in the lung of the Co-infection group showed higher viral load at 4 dsc, comparing to the SIV-infected group significantly. The results suggest that the low pathogenic pdmH1N1 SIV could enhance the lung severity when co-infected with the HP-PRRSV possibly leading to porcine respiratory disease complex (PRDC).