Research On Antigen Dynamic Distributions In Piglets After Infection With Virulent Or Low Virulent GD Strian Of Highly Pathogenic PRRS Virus

Highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) is an acute highly lethal disease caused by a highly pathogenic variant of American-type PRRSV strains. It has induced serious economic losses farming industry since 2006 the disease outbreaked in China. Clinical symptom mainly show fever, abortion, high morbidity and high mortality characteristics in infected pigs. It is one of the most serious diseases in China's pig industry. Study results confirmed the characteristic gene lack of HP-PRRSV NSP2 region without relationship with their pathogenicity.At present, there are some genotypes and subtypes in PRRSV and different virulence virus can cause different responses to the host target. The protection of the traditional inactivated vaccine is often very limited in pigs, can not preventing pigs from infection HP-PRRSV. The cross-protection of HP-PRRSV strains and classal attenuated vaccine strain is also very limited in pigs, even if only small difference in genotype, which is currently the biggest problem prevention and control of PRRS. Therefore, further research and development of new PRRS vaccine and to develop a more rational prevention and control programs on the pig industry in China is significant.In this study, by comparing with the sequence of ORF6 and ORF7 reading frame of several the Inter-American PRRSV strains, primers and probes were designed by selected conserved regions, PRRSV antigen detection methods of RT-PCR and Taqman RT-PCR were established. The results showed the specificity and sensitivity of the methods are good, Taqman RT-PCR is 10-100 times more sensitive than conventional RT-PCR.Through RT-PCR and Taqman quantitative RT-PCR methods were established in my laboratory for detection antigens of attenuated vaccine strains GDr180 and virulent strain GDF5 of PRRSV in infected piglets tissues and organs during 40 days after infected, to compare with distribution strength differences of the 2 strains in tissue tropism, which further reveal the pathogenic mechanism change of attenuated vaccine strains. The results showed that the strength of strain in organ and tissue differences in the distribution of significant and continuous lifetime distribution is also quite different. Virulent strain appeared at 1 weeks after infected,2 weeks the antigen distribution range is the widest. distribution range after 3 weeks was significantly reduced; relative to the virulent strain, the attenuated strain appeared is relatively late in infected tissue, only revealed between 2 to 3 weeks after infected. Both 2 strains were disappeared after 5 weeks in pigs. From the distribution point of view, the virulent strain(GDF5) is more broader in tissues and organs of pigs tropism than attenuated(GDr180), and attenuated is mainly in the lung and lymph nodes. Description virulent strain during passage in cells decreased virulence, while the range of tissue tropism is also significantly reduced, which may be the long-term virus and cell to adapt to each other.In this study, the low virulent strain GDr180 stimulates the production of different immune doses of PRRSV antibodies were detected by ELISA method, though test results of the experiment is the antibodies against N protein, it does not play the role of neutralize the virus, however, the body's immune response and pigs have great relevance. Optimal immunization dose selection is Significance, but the best dose immunization needs further testing to determine.