Epidemiologic Survey Of Highly Pathetic Porcine Reproductive And Respiratory Syndrome In Guangxi And Cloning And Sequencing Of ORF5, ORF6, ORF7 Genes

38 pig farms infected suspect PRRS in 12 areas of Guangxi,including Baise,Hechi, Yulin,Nanning,Hezhou,Guigang,Chongzuo,Fangchenggang,Liuzhou,Qinzhou and Guilin,were investigated in this study,The blood serum,lung,spleen and lymph node of infected pigs were tested by RT-PCR,and total of 104 the PRRS positive material were detected.This study show highly pathogenic PRRS spread fast and is prevalent in many places of Guangxi,with high morbility rate and typical symptom and pathological lesion. The abortion rate of infected sow is 100%.The morbility and mortality rate of suckling pigs is 100%and 60-100%respectively,that of nursery pigs and fattening pigs is quite low.The ORF5,ORF6 and ORF7 gene of the 18 PRRS isolates were cloned and sequenced.The result showed between the 18 PRRS isolates,the homology of nucleotide and deduced amino acid of ORF5,ORF6,ORF7 were 97.7～100%,98.3～100%,98.4～100% and 97.0～99.5%,97.1～99.4%,95.2～99.2%respectively.Compare the 18 PRRS isolates with American typical strain VR-2332,the homology of nucleotide and deduced amino acid of ORF5,ORF6,ORF7 were 88.4～89.7%,94.3～95.4%,93.5～94.4%and 87.1～88.6%, 94.9～97.1%,90.3～96.0%respectively.Compare with European strain LV,the homology of nucleotide and deduced amino acid of ORF5,ORF6,ORF7 were 63.2～64.6%, 68.2～69.0%,65.1～65.9%and 57.5～58.0%,77.1～78.9%,55.6～58.9%respectively. Indicating the 18 PRRS isolates belong to American strain.And compare the 18 PRRS isolates with 6 Guangxi isolates in 2006,the homology of amino acid of ORF5,ORF5, ORF7 were 86.1～96.0%,93.1～96.6%and 88.7～97.6%. According to the mutation of the E protein,compared the 18 PRRS isolates with the Guangxi isolate GXA,which belongs to groupⅠand was isolated in 2002,the homology of nucleotide and deduced amino acid of E gene was 88.4～89.6%and 86.1～87.6%.and compared with groupⅡGXWX isolate,the homology of nucleotide and deduced amino acid of E gene was 89.1～90.5 and 88.6～90.5%,the homology was quite low.But compared with JXA1,HUB2,HEB1 and HuN strains,the homology were quite height which was 98.5～99.7%and 97.5～99.5%.Illustrating that Guangxi isolates have a great change since 2006,and have a high homology with high pathetic strains JXA1,HUB2, HEB1 and HuN.The mutation sites of amino acid of E protein of the 18 PRRS isolates mainly concentrate in 24～39,58～66,92～104,161～164 and 185～200 sites.That of M protein mainly concentrate in 10,63～70 sites.That of N protein mainly concentrate in 46,91,109 and 117 sites.The phylogenetic tree show the 18 PRRS isolates of Guangxi together with CH-1a strain belong to groupⅡ,and have a close relationship with high pathetic strains JXA1, HUB2,HEB1 and HuN,indicating that probably originate from a same strain.