Identification of enterobacteria in viscera of pigs afflicted with porcine reproductive and respiratory syndrome and other viral co-infections

Authors: ZHAO, GE - China Animal Health And Epidemiology Center; ZHANG, LUJIE - Jiangxi Agricultural University; Li, Charles; ZHAO, JIANMEI - China Animal Health And Epidemiology Center; LIU, NA - China Animal Health And Epidemiology Center; LI, YUEHUA - China Animal Health And Epidemiology Center; WANG, JUNWEI - China Animal Health And Epidemiology Center; LIU, LIHENG - Jiangxi Agricultural University

Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2020
Publication Date: 7/11/2020
Citation: Zhao, G., Zhang, L., Li, C.Z., Zhao, J., Liu, N., Li, Y., Wang, J., Liu, L. 2020. Identification of enterobacteria in viscera of pigs afflicted with porcine reproductive and respiratory syndrome and other viral co-infections. Microbial Pathogenesis. 147:10385.

Interpretive Summary: Porcine reproductive and respiratory syndrome (PRRS) is a swine viral disease which poses a significant economic threat to the swine industry worldwide. The PRRS virus (PRRSV) can infect pigs of various ages and cause different clinical symptoms. When the virus infects nursery pigs, it causes respiratory disorder, but may not directly result in death if no secondary infection occurs, unless pigs infected with some highly pathogenic PRRSV isolates. Therefore, secondary infection is usually one of the main reasons responsible for death in PRRS infected pigs. In order to investigate pathogenic enterobacteria presence involved in the secondary infections in PRRS pigs with different viral co-infections, the authors identified intestinal bacteria strains (called enterobacteria) for aiding in clinical treatment. Twenty-one diseased pigs were diagnosed with the PRRS virus (PRRSV) and other 7 virus primers by PCR/RT-PCR in the lung and spleen samples. Enterobacteria strains were isolated using agar culture from 5 visceral samples of PRRS pigs, and identified by 16S rDNA genomic sequencing. PRRSV was positive in 100% of the lung samples and 81.0% of the spleen samples. Seven diseased pigs were diagnosed with only PRRSV infection (33.3%), 7 pigs with PRRSV and 1 or 2 other viruses (33.3%) and 7 pigs with PRRSV and more than 2 types of other viruses (33.3%). PRRSV was more inclined to co-infect pigs with porcine group A rotavirus (PARV) with the co-infection rate of 52.4% (11/21). Approximately 13 types of bacteria were successfully isolated from lung, spleen, liver, kidney and lymph node samples of different PRRS pigs. Enterobacteria strains were isolated in 100% of lung, liver and lymph samples from pigs infected with PRRSV alone. However, the isolation rates were significantly decreased in the more than 3 viruses co-infection group. Escherichia coli was the most prevalent bacterium, followed by several kinds of bacteria, including common Shigella and Salmonella pathogens. Most of the isolated enterobacteria strains were opportunistic pathogens. Therefore, timely identification of bacteria in the infected tissues and combination with antimicrobial agents are necessary for effective treatment of PRRS-infected pigs.

Technical Abstract: In order to investigate enterobacteria presence involved in the secondary infections in Porcine Reproductive and Respiratory Syndrome (PRRS) pigs with different viral co-infections, we identified enterobacteria for guiding clinical treatment. Twenty-one diseased pigs were diagnosed with the PRRS virus (PRRSV) and other 7 virus primers by PCR/RT-PCR in the lung and spleen samples. Enterobacteria were isolated using MacConkey agar from 5 visceral samples of PRRS pigs, and identified by 16S rDNA sequencing. PRRSV was positive in 100% of the lung samples and 81.0% of the spleen samples. Seven diseased pigs were diagnosed with only PRRSV infection (33.3%), 7 pigs with PRRSV and 1 or 2 other viruses (33.3%) and 7 pigs with PRRSV and more than 2 types of other viruses (33.3%). PRRSV was more inclined to co-infect pigs with porcine group A rotavirus (PARV) with the co-infection rate of 52.4% (11/21). Approximately 13 types of bacteria were successfully isolated from lung, spleen, liver, kidney and lymph node samples of different PRRS pigs. Enterobacteria were isolated in 100% of lung, liver and lymph samples from pigs infected with PRRSV alone. However, the isolation rates were significantly decreased in the more than 3 viruses co-infection group. Escherichia coli was the most prevalent bacterium, followed by Morganella, Proteus, Shigella, Salmonella, Klebsiella and Aeromonas. Most of the isolated enterobacteria were opportunistic pathogens. Therefore, timely combination with antimicrobial agents is necessary for effective treatment of PRRS-infected pigs.