Immunopathology And Molecular Pathology Evaluation On The Attenuated Effect Of High Pathogenic Porcine Reproductive And Respiratory Syndrome Virus

In 2006, the highly pathogenic porcine reproductive and respiratory syndrome were outbreak in mainland of China. A lot of areas from the large-scale farms to the rural households had been attacked in varying degrees in the south. Different ages and weights swine can be aggressed and the performance of infected swines were high fever (41-42℃), drowsiness, difficulty in breathing. The infected rate was 100% and the mortality rate can reach to 50% in pigs. The abortion of sow was highly up to 30%. Foster pigs can be attacked to death. Pathogen were the variant which were American classical- PRRSV in part Nsp2 Department ORF1a gene deletion mutant. The incubation period of HPPRRSV can last 2-7 days, infected pigs mainly showed high fever, pregnant sows at various stages were miscarriage, stillbirth and back-up pigs can be attacked to death. Suckling piglets and foster pigs were also infected and had higher mortality rates.In order to evaluation the attenuated effect of high pathogenic porcine reproductive and respiratory syndrome virus (HPPRRSV) and screen the attenuated vaccine candidate, fifty-two 40-42 days old pigs were inoculated with HPPRRSV HUN4 strain and its attenuated strain HUN4-Fxx respectively. Pigs from these groups were necropsied at 1, 3, 5, 7, 10, 14, 21 and 28 days postinoculation. We took heat, liver, spleen, lung, kidney, submandibular lymph nodes, mesenteric lymph nodes, inguinal lymph nodes, cerebrums, intestines, stomach and tonsil and fixed with 4% paraformaldehyde for pathology. Gross lesions shown pigs demonstrated death after incoculated with HUN4 frome 5 to 21 days . Lymphoid node were hemorrhage, the edges of spleen necrosis,gray-white nodule were seen in liver, lung had hypertrophy and hyperplasia and multifocal septal thickening, Brain had mild edema. Miscroscopic lesions were as follows. The multifocal interstitial pneumonia was prestent. Lymphocytes necrosis and decreased and foci of eosinophile granulocyte cell infiltrates were seen in the paracortical zone and medullary region. Necrosis and decrease of lymphocytes were also detected in spleen and tonsil. Eosinophile granulocyte cell infiltrated present in the tonsil. Lymphocytic infiltration around blood vessels in cerebrums. Lymphocytic cuffing around blood vessels in molecular layer. Contrastly, there were no obviously clinical and gross changes and lymphocytes necrosis and decrease were mild in immune organs of inoculated with HUN4-Fxx pigs in pathohistology.We used indirect immunofluorescence assay (IFA), immunohistochemical procedrues (IHC) for PRRSV antigen and in situ hybrisization for PRRSV nucleic acid. The percentage of PRRSV antigen in pigs which inoculated with HUN4 or HUN4-Fxx were different by using three ways . Lungs were 33.33%,0%;75%,37.5%;95.8%,62.5%, respectively. Tonsils were 87.5%,62.5%;91.7%,87.5%;95.8%,87.5 %, respectively. Spleens were 45.8%,37.5%;83.33%,50%;66.7%,56.25%, respectively. Submandibular lymph nodes were 91.6% ,75% ;100%,100% ;100%,87.5%, respectively. Mesenteric lymph nodes were 87.5% ,68.75% ;95.8%,87.5% ;100%,87.5% , respectively. Inguinal lymph nodes were 95.8%,81.25% ;100%,81.25%;100%,87.5% , respectively. Cerebrums were 4.16%,0%;12.5%,0% ;16.7%,0% , respectively. Intestines were 54.16%,37.5% ;83.33%,56.25% ;87.5%,56.25% , respectively. Kidneys were 37.5% ,18.75% ;58.33%,25%;0%,0% , respectively. There were no positive cells in heart, liver and stomach.Positive reaction fluorescence achieved the most strong during 10-14DPI inoculated with HUN4 in IFA, whereas postitive reaction was gentle inoculated with HUN4-Fxx strain. Antigen was most intense from 3-21DPI in HUN4 group of IHC and two groups had significantly distinction. PRRSV nucleic acid was most intense from 3-21DPI in HUN4 group of ISH and the quantity of postive cells of two groups were notable differently. The positive signals were detected in the endothelium of glomerulus by IFA, IHC except ISH. PCR results of kidneys in HUN4-Fxx group and th most of HUN4 group were negative. According to above results, we presumed the postive reactions wer antigen-antibody complex.The research results showed that the distribution of attenuated strain HUN4-Fxx in the immune organs were not different with HUN4, whereas the HUN4-Fxx strain lead to the degree of lesions were obviously decreased. The HUN4-Fxx strain could not be detected in cerebrums and in lung which virus target organ detection rate were significant lower than HUN4 and no obviously clinical and pahtological changes. All above researches indicated the virulence were notable decreased and could be the strain for the attenuated vaccine.