The Study On Pathogenic Of Coinfection With Porcine Circovirus Type2 (WH Strain) And Porcine Reproductive And Repiratory Syndrome Virus

Porcine circovirus type 2 (PCV2) is considered as the major causative agent of post-weaning multisystemic wasting syndrome (PMWS). At present, PCV2 is widely spreaded in the world and maintain high infection rate in herd. The PMWS affected pigs display systemic lymphoadenopathy and interstitial pneumonia. The istopathological lesions of lymphoid tissues in PMWS-affected pigs are variable lymphoid depletion in B-and T-cell dependent areas combined with histiocytic and/or multinucleated giant cell infiltration in lymphoid follicles. The often coexistence of PRRSV in PMWS-affected pigs and the enhanced PCV2 replication and tissue distribution in PCV2 and PRRSV dually-infected pigs imply that PCV2 and PRRSV may interact in the pathogenesis of PMWS. However, how PCV2 interact with PRRSV is still unkown. So in our research we used PAMs as model to test the effect on PAMs by co-infecting with PCV2 and PRRSV; then study the effect of co-infection with PCV2 and PRRSV on piglets.1. Effect of coinfection with PCV2 and PRRSV on PAMs in vitroIn order to determine pathogenesis of co-infection with PCV2 and PRRSV, PAMs were prepared and infected with PCV2 and PRRSV alone or together with the different orders. The copies of PCV2 in supernatant and cells were detected by real-time PCR and IFA; the cytopathic effect (CPE), livability and apoptotic cells of PAMs were monitored and calculated. The results were as followed:(1) PCV2 showed neither no replication nor induced CPE following infection; PRRSV could induce CPE, the PCV2 and PRRSV co-infection could not enhance PCV2 replication in PAMs.(2) The PCV2 singular infection group had high antigen-containing rate and the positive cells displayed a homogeneous distribution, however, co-infection groups were not significantly different from PCV2 singular infection, they showed a pinpoint to small granular.(3) A higher apoptosis were seen in PRRSV alone infected pigs and PCV2 and PRRSV dually infected groups but no apoptosis were seen in singular PCV2 alone infection group.(4) Co-infection with PCV2 and PRRSV increased the expression of TNF-α,IL-8 while decreased the expression of IFN-γ, as comparing to singular infection, thus enhanced the pathological reaction. 2. Effect of experimental co-infection with PCV2 and PRRSV on pigletsAn attempt was made to value the co-infection effects with PCV2 and PRRS Von the four-week-old post-weaning piglets. Four groups were studied, including mock-infected (n=5), PCV2 alone-infected (n=5),PRRSV alone-infected(n=5), and PCV2 and PRRSV dually infected groups(n=5), to compare the differences.We studied the pathogenicity of co-infected with PCV2 and PRRSV through methods of clinical symptom, viremia, viral levels in rectal swab, pathological changes and the virus distributions in different tissues.(1) The results showed us that the co-infection with PCV2 and PRRSV caused higher fever, deprementia, progressive weight loss, more sever than and virus singular infection.(2) We got to know from the detection of virus level in serum and rectal swab that PCV2 exists in serum through the whole experimental period, and pigs co-infected with PCV2 and PRRSV showed higher lever of PCV2 than singular PCV2 infection. Besides from 7 dpi to 21 dpi, we could detect existence of PCV2 in rectal swab in both singular PCV2 infection pigs and PCV2/PRRSV co-infection pigs.(3) Co-infection with PCV2 and PRRSV resulted in the similar pathological change with PMWS, and was more severe than either of singular virus infection, including severe interstitial pneumonia and Lymphatic congestion, enlargement. The detection of PCV2 in different tissues showed that PCV2 mainly replicated in immune organ and tissues (spleen, tonsil and lymph nodes), and the PCV2/PRRSV co-infection enhanced the replication of PC2 in tissues, thus causing the tissue lesion more severe.