The Pathogenicity Evalueation Of PRRSV And PCV2 Coinfection To Piglets

The entire genomes of one isolate of porcine circovirus type 2 (PCV2) from pigs with postweaning multisystemic wasting syndrome (PMWS) was cloned and sequenced. The result indicated that the PCV2 isolate complete genomes is 1767bp, and its sequence is closely identity with an France isolate (GenBank:AF055394), up to 99.4%.It was that cloned and expressed in a prokarytoic expression system to the fragment of cap gene of PCV2, and we got the fusion protein His-CAP520. The experiments showed that this fusion protein has good antigenicity.and the indirect ELISA method was established for detecting the bodies of PCV2 with this protein.An attempt was made to value the coinfection effects of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) to the three-week-old post-weaning piglets. Three groups were studied, including mock -infected (n=3), PRRSV alone-infected ( n=3 ) , and PCV2 and PRRSV dually infected groups(n=5), to compare the differents. We studied the pathogenicity of cochallenged with PRRSV and PCV2 through methods of clinical symptom , pathological changes , etiology and serology.By 4days postinoculation(4dpi), PCV2 and PRRSV challenged pigs had severe dyspnea, fever, after 14dpi, one pig was dead. PRRSV-challenged pigs developed dyspnea and mild lethargy that resolved by 28dpi, and the control pigs were normal. In PCV2 and PRRSV group, we found mass of proliferative interstitial pneumonia, Lymph node and spleen follicle collapsed and faintness of boundary, endochylema saccharogen in liver cell was lost by pathological section.Microscopic lesions consistent with postweaning multisystemic wasting syndrome (PMWS). PRRSV-challenged pigs had moderate proliferative interstitial pneumonia, but did not develop bronchiolar or hepatic lesions or lymphoid hemorrhage. In coinfection group, both of the virus antigens were distributed predominantly in lymph nodes and lungs, followed by livers and spleens, seldom in kidneys, comparatively the distribution of PRRSV in cochallenged group is more extensive than PRRSV-alone group. In cochallenged group , the antibodies of PCV2 was appeared at 7dpi, and went to the highest level at 14dpi , and the PRRSV antibodies went up at 14dpi and went to the top at 21dpi. It is like the PRRSV-challenged pigs to the growth and decline pattern of PRRSV antibodies in coinfection group. Especially in toxemia period the virus antigens could be detected in th tissues easily. Both of virus were found at 4dpi in sera by PCR and RT-PCR, similar to the PRRSV-alone group, and maintained to the end of the experiment. That is to say the viremia is long lasting in the body of piglet's.The results indicate that PCV2 coinfection increases the severity of PRRSV-induced interstitial pneumonia in pigs and induces the lymphoid deplationgranulomatous inflammation, and necrotizing hepatitis characteristic of PMWS. But cochallenge can result to bronchopneumonia and hepatitis obviously, and massive hemorrhage bounded. This clinical symptoms is classical pathological change in the cochallenge of PRRSV and PCV2 group.