Porcine reproductive and respiratory syndrome virus (PRRSV) is an epidemic etiology in pigs of all ages causing reproductive failure and respiratory manifestation. PRRSV has been circulating in Chinese pig farms for almost 20 years. The aim of the present study was to fully understand the extent of the genetic diversity and molecular characteristics of PRRSVs in Central China. A strain of PRRSV isolated from a recent outbreak farm in Hunan province in Central China, designated HUN-2014, was sequenced and analyzed with 39 other PRRSVs from 1998 to 2014 in Central China. Comparative results of genomic sequences revealed that all 40 PRRSVs belonged to the North American genotype (NA genotype) and shared 88.8-99.0% homology. Phylogenetic analysis showed three subgenotypes, namely conventional PRRSV (C-PRRSV), specially mutant PRRSV (S-PRRSV) and highly pathogenic PRRSV (HP-PRRSV), in all 40 PRRSVs. Moreover, comparative analysis of amino acid (AA) sequences of NSP2, GP3, GP5 and ORF5a revealed the main evolution trend of PRRSVs in Central China from 1998 to 2014, which was from C-PRRSV to HP-PRRSV, accompanied by different evolving directions to S-PRRSV. In conclusion, both the major evolutionary trend and special features of genetic variation should be emphasized as theoretical basis for development of new vaccines and control strategies for PRRS.

为了比较两种猪瘟病毒抗体检测试剂盒对猪瘟疫苗免疫抗体的检测结果,本试验将27头猪瘟抗体阴性仔猪免疫猪瘟活疫苗后7、10、14、17、20、23、27、30、34 d共9个时间点采血,分别用两种猪瘟病毒ELISA抗体检测试剂盒进行抗体检测,同时采用OIE指定方法-荧光抗体病毒中和试验对检测结果进行验证.结果表明,虽然两种试剂盒均可在免疫后30 d 100％检测到免疫猪体内的猪瘟抗体,但国产试剂盒在疫苗免疫后第10天便可在6/21猪体内检测到猪瘟抗体,20 d时抗体检测全为阳性,而美国IDEXX公司的试剂盒在疫苗免疫后27 d才在11/21猪体内检测到猪瘟抗体,30 d时才全部变为阳性,而两种试剂盒对6头阴性对照猪血清连续跟踪检测34 d均为阴性.由此可以得出结论:国产试剂盒在疫苗免疫后的早期抗体检测中敏感性明显离子IDEXX公司的试剂盒.

Due to the urgent need of differentiation of infected from vaccinated animals in control and eradication of classical swine fever (CSF) and the shortcomings of current differential diagnostic tools, this study is aiming to establish a RT-nestPCR assay for differential detection of wild-type viruses and lapinized Chinese vaccine strain (C-strain) of classical swine fever virus (CSFV) of high sensitivity. Two pairs of CSFV-specific primers were designed in the conservative regions of NS5B (a non-structural protein encoded by the CSFV genome, which performs the RNA dependent RNA polymerase activity) and 3? un-translated regions (3?-UTR) to encompass the T-rich insertion uniquely existing in the 3?-UTR of C-strain genome. Thus the amplification fragment of C-strain is longer than that of the wild-type viruses for it contains the T-rich insertion region. Two pairs of primers were used in combination and the wild-type viruses and C-strain of CSFV could be detected and accurately distinguished with a high sensitivity through super fine resolution (SFR) argarose gel electrophoresis that displays the different lengths of the amplicons. The detection limit of the C-strain and Shimen strain were respectively 4.5×10-2 pg and 3.2×10-2 pg of viral RNA. The results of the specificity test showed that this method can detect different strains of CSFV without amplifying other non-CSFV pathogens. The results of the detection of 400 clinical samples indicated that 16 samples were CSFV positive in total; in which 4 samples were C-Strain positive and 12 were wild-type CSFV positive. The total CSFV positive rate was 4%. The detection results of the 14 batches of C-Strain vaccines showed that all samples displayed bands of C-Strain amplicons in the SFR argarose gel electrophoresis and all vaccines were free of wild-type virus contamination. In conclusion, the RT-nestPCR assay established in the present study could supply a sensitive and specific test method for distinguishing wild-type CSFV infected animals from those vaccinated with C-strain vaccines in the field.