|Meng, Xiang jin|
Submitted to: Veterinary Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/9/2012
Publication Date: 7/6/2012
Citation: Opriessnig, T., Gauger, P.C., Faaberg, K.S., Shen, H., Beach, N.M., Meng, X., Wang, C., Halbur, P.G. 2012. Effect of porcine circovirus type 2a or 2b on infection kinetics and pathogenicity of two genetically divergent strains of porcine reproductive and respiratory syndrome virus in the conventional pig model. Veterinary Microbiology. 158(1-2):69-81. Interpretive Summary: Porcine circovirus type 2 (PCV2) has been implicated in exascerbating clinical disease in swine infected with porcine reproductive and respiratory syndrome virus (PRRSV). The manuscript describes the clinical disease of swine after infection of high health swine concurrently with either of two subtypes of PCV2 (2a and 2b) and either of two strains of PRRSV (92 and 06). Coinfection of pigs with PRRSV-92 or PRRSV-06 and PCV2a or PCV2b revealed that PRRSV-06 infected pigs had somewhat higher amounts of PRRSV RNA, which was associated with lower numbers of lymphocytes and lower amounts of PCV2 DNA on days 9 and 12 only (respectively), compared to PRRSV-92 pigs. Moreover, PCV2b infected pigs had somewhat higher amounts of PCV2 DNA on dpi 3 and increased IFNg levels on dpi 6, when compared to PCV2a infected swine. These results are different from previous single-infection models and emphasizes the importance and impact of coinfecting pathogens on virus kinetics.
Technical Abstract: The objective of this study was to characterize the infection dynamics and pathogenicity of two heterologous type 2 porcine reproductive and respiratory syndrome virus (PRRSV) isolates in a conventional pig model under the influence of concurrent porcine circovirus (PCV) subtype 2a or 2b infection. Forty-four conventional PCV2 and PRRSV naïve pigs were randomly assigned to one of five rooms and groups each containing 8 or 9 pigs: Negative controls (n=8); coinfected with a 1992 PRRSV (PRRSV-92) and PCV2a (CoI-92-2a; n=9), coinfected with PRRSV-92 and PCV2b (CoI-92-2b; n=9), coinfected with a 2006 PRRSV (PRRSV-06) and PCV2a (CoI-06-2a; n=9) and coinfected with PRRSV-06 and PCV2b (CoI-06-2b; n=9). Inoculation was conducted at approximately 23 days of age. Blood samples were collected from all pigs prior to inoculation and at day post inoculation (dpi) 3, 6, 9 and 12 and tested for the presence of PRRSV antibody, PRRSV RNA, PCV2 antibody, PCV2 DNA, blood counts, and interferon gamma (IFNg) levels. Coinfection of pigs with PRRSV-92 or PRRSV-06 and PCV2a or PCV2b revealed that PRRSV-06 infected pigs had significantly higher amounts of PRRSV RNA on dpi 9 and 12 which was associated with significantly lower numbers of lymphocytes on dpi 9 and significantly lower amounts of PCV2 DNA on dpi 12 compared to PRRSV-92 pigs. Moreover, PCV2b infected pigs had significantly higher amounts of PCV2 DNA on dpi 3 and significantly increased IFNg levels on dpi 6 compared to pigs infected with PCV2a which is different from previous singular infection models emphasizing the importance and impact of coinfecting pathogens on virus kinetics. Further investigations are necessary to elucidate the specifics of the PCV2-PRRSV interaction in swine.