Molecular Epidemiological Investigation Of Porcine Circovirus Type2in Shaanxi Province And Identification Of Natural Inter-genotype Recombinants

Porcine Circovirus (PCV) is the major etiological agent of porcine circovirus associateddiseases (PCVD), which is a multisystem disease of pigs characterized by postweaningmultisystemic wasting syndrome (PMWS) multisystem disease of pigs.PCV compose of twosubtype PCV type1and PCV type2according to serotype. PCV1has no pathogenic, butPCV2is a major pathogen that caused PCVD. Since PCV2was first detected in2000inChina, Then, many scholars has carried on the investigation and analysis the prevalence ofPCV2in different areas different provinces in China. Results showed that PCV2was not onlyhigh infection in our country, but also caused a huge impact on the development of pigindustry in China. The study was done to investigate the molecular epidemiology of provincecircovirus type2(PCV2) and provide reference for further prevention and clinical treatmentof PCV2-infected pigs. We obainted the following results:1. Molecular epidemiological investigation of porcine cicovirus type2Shaanxi provinceA total of141samples were collected between2010and2012from diseased pigs fromdifferent places such as Xi’an, Xianyang, Baoji, Yuling, Yan’an in Shaanxi province of China.First, PCV2positive sample were identified by classical PCR in these141samples. ThenPCV2positive DNAs were further identified by genotype-specific PCR assay. Finally, PCV2ORF2gene was amplified, cloned and sequenced, and then the sequences were analyzed bybioinformatics analyses. The results showed that117/141(82.9%) diseased pigs were positivefor PCV2, while32/33dead pigs were positive for PCV2. Genotype-specific PCR detectionshowed that59of117PCV2positive samples were identified as PCV2b-single infection, and11of117were identified as PCV2a-single infection,47of117were identified as mixedinfection with PCV2a and PCV2b. Analysis of the PCV2ORF2sequences of32samplescollected from death pigs showed that evolutionary relationships of12strains were near toPCV2b-1A/1B,16strains near to PCV2a-1C,4strains near to PCV2a; Analysis of ORF2acidamino sequences showed that most of mutation sites were located at8-47,59-101,134-169and180-210these four regions. PCV2infection is serious in Shaanxi province, meanwhile, PCV2b-1A/1B and PCV2b-1C are pandemic strains. Amino mutation sites were mainlylocated at cap protein potential epitope area.32PCV2positive clinical samples from thediseased and dead pigs were identified by classic PCR.2. Identification of natural inter-genotype recombiants15of32clinical samples were identified as infection with both PCV2a and PCV2b. weamplified and sequenced the full-length of these15samples and used recombination analysissoft analized the sequences.The results showed that13of15mixed infection were recombiantstrains of PCV2a and PCV2b. Using base-by-base comparison and recombinant detectionanalyses of the full-length sequences of these strains suggest that the recombination crossoverregions mainly located in ORF2. Recombinant clusters were divided into two parts: Cluster1and Cluster2. Cluster1included3recombinant strains, and cluster2included10recombinant strains. These results demonstrate that recombination between PCV2a andPCV2b strains can occur in cap protein coding region through different patterns and yielddifferent recombinants. Our study not only provided new evidences that PCV2strains canundergo recombination through a variety of patterns, but also suggests that the occurrence rateof recombination events is high in the co-existence, especial in serious infection case, ofdifferent strains of PCV2.This study found that PCV2infection is serious in Shaanxi province, meanwhile,PCV2b-1A/1B and PCV2b-1C are pandemic strains. Deeply analysised results showed that13of15mixed infection were recombiant strains of PCV2a and PCV2b. Recombinant clusterswere divided into two parts: Cluster1and Cluster2. Cluster1included3recombinant strains,and cluster2included10recombinant strains. The results help us to understand new infectionand prevalence forms of PCV2clinically in Shaanxi province, and provide theoreticalinstruction for prevention and clinical treatment of PCV2-infected pigs.