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[Genetic variation and pathogenicity analysis of highly pathogenic porcine reproductive and respiratory syndrome virus strain TJ in the course of attenuation].

Division of Zoonosis, Institute of Special Economic Animal and Plant Sciences, Chinese Academy of Agricultural Science, Jilin 132109, China.
Bing du xue bao = Chinese journal of virology / [bian ji, Bing du xue bao bian ji wei yuan hui] 03/2012; 28(2):136-42.
Source: PubMed

ABSTRACT 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.

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    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 (10(5.0) 50% tissue culture infective doses [TCID(50)]) 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.
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