[Genetic variation and pathogenicity analysis of highly pathogenic porcine reproductive and respiratory syndrome virus strain TJ in the course of attenuation]
To develop an attenuated vaccine against the highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) virus, the HP-PRRS virus strain TJ was attenuated by serial passages and plaque cloned every 5 to 10 passages in Marc-145 cells. Genetic variation and pathogenicity of HP-PRRSV strain TJ in the course of attenuation were analyzed. The results showed that the strain TJ sustained various sequence changes during the course of attenuation. Fifty-eight amino acids changes and a new continuous 120 amino acids deletion after the discontinuous 30 amino acids deletion (sites 481 and 533-561) occurred in strain TJ passages 140, and the position of 120 amino acids deletion was between 628 to 747 according to VR-2332. Animal test showed that the pathogenicity of strain TJ passages 20 was attenuated obviously, so we presume that genetic variation in nonstructural protein nsp2-nsp5, nsp7 and structural protein GP5 during the attenuation provides the molecular bases for the observed attenuated phenotype.
- [Show abstract] [Hide abstract] ABSTRACT: Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) is characterized by high fever and high mortality in pigs of all ages and has severely affected the pork industry of China in the last few years. An attenuated HP-PRRSV strain, TJM, was obtained by passaging HP-PRRSV strain TJ on MARC-145 cells for 92 passages. Porcine reproductive and respiratory syndrome virus (PRRSV)- and antibody-free pigs were inoculated intramuscularly with TJM (105.0 50% tissue culture infective doses [TCID50]) and challenged at 28, 60, 120, and 180 days postimmunization (dpi). The results showed that 5/5, 5/5, 5/5, and 4/5 immunized pigs were protected from the lethal challenge and did not develop fever and clinical diseases at each challenge, respectively. Compared to control pigs, vaccinated pigs showed much milder pathological lesions and gained significantly more weight (P < 0.01). Sequence analysis of different passages of strain TJ showed that the attenuation resulted in a deletion of a continuous 120 amino acids (aa), in addition to the discontinuous 30-aa deletion in the nsp2 region. The analysis also demonstrated that the 120-aa deletion was genetically stable in vivo. These results suggested that HP-PRRSV TJM was efficacious against a lethal challenge with a virulent HP-PRRSV strain, and effective protection could last at least 4 months. Therefore, strain TJM is a good candidate for an efficacious modified live virus vaccine as well as a useful molecular marker vaccine against HP-PRRSV.0Comments 15Citations
- [Show abstract] [Hide abstract] ABSTRACT: Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) was reported in the late 1980s. PRRS still is a huge economic concern to the global pig industry with a current annual loss estimated at one billion US dollars in North America alone. It has been 20 years since the first modified live-attenuated PRRSV vaccine (PRRSV-MLV) became commercially available. PRRSV-MLVs provide homologous protection and help in reducing shedding of heterologous viruses, but they do not completely protect pigs against heterologous field strains. There have been many advances in understanding the biology and ecology of PRRSV; however, the complexities of virus-host interaction and PRRSV vaccinology are not yet completely understood leaving a significant gap for improving breadth of immunity against diverse PRRS isolates. This review provides insights on immunization efforts using infectious PRRSV-based vaccines since the 1990s, beginning with live PRRSV immunization, development and commercialization of PRRSV-MLV, and strategies to overcome the deficiencies of PRRSV-MLV through use of replicating viral vectors expressing multiple PRRSV membrane proteins. Finally, powerful reverse genetics systems (infectious cDNA clones) generated from more than 20 PRRSV isolates of both genotypes 1 and 2 viruses have provided a great resource for exploring many innovative strategies to improve the safety and cross-protective efficacy of live PRRSV vaccines. Examples include vaccines with diminished ability to down-regulate the immune system, positive and negative marker vaccines, multivalent vaccines incorporating antigens from other porcine pathogens, vaccines that carry their own cytokine adjuvants, and chimeric vaccine viruses with the potential for broad cross-protection against heterologous strains. To combat this devastating pig disease in the future, evaluation and commercialization of such improved live PRRSV vaccines is a shared goal among PRRSV researchers, pork producers and biologics companies. Copyright © 2015. Published by Elsevier Ltd.0Comments 5Citations