Pathogen Detection And Genetic Evolution Analysis Of PCV2 And PCV3 In Slaughter Pigs Of A City In Guangxi

Circovirus spread widely and general infection is found in the domestic and foreign pig industry.The circovirus related diseases have been caused a huge economic loss.Circovirus invade the pig's lymphatic system which lead to reduction of the lymphocytesand compromising of immune systems,resulting in herds can't grow healthily.Slaughterhouse is an important part of the safe pork industry chain,which is responsible for the final treatment of live pigs.Strict pathogen detection is needed to prevent further spread of pathogens.In this study,181 lymph nodes from slaughterhouse in Guangxi in June 2017 to August 2017 were collected.PCV2 and PCV3 infection in in healthy slaughter pigs was detected by PCR method.The results showed that the positive number of PCV2 was 108.The positive rate was 59.67%;The positive number of PCV3 was 44,the positive rate was 24.31%;The positive number of the coinfeciton of PCV2 and PCV3 t was 27.The rate of co-infection of PCV2 and PCV3 was 14.92%.This suggests that the infection of circovirus in healthy pigs is more severe.In this study,five PCV2 full sequences(1767bp)and six PCV3 full sequences(2000bp)were amplified,cloned and sequenced.The genetic phylogenetic trees were consctructed based on the full length sequences.The results showed that the nucleotide homology of 5 PCV2 sequences was 96.1%-99.5%,the nucleotide homology of 5 ORF2 was 94.0%-99.7%,and the homology of 5 amino acids was 94.0%-100.0%.Compared with other reference PCV2 strains,the PCV2b type,especially is PCV2b-1C,was the predominant genotypes in Guangxi.The genetic phylogenetic trees of PCV3 showed that the nucleotide homology among the sequences was 98.6%?99.4%and the nucleotide homology among the ORF2 was 97.2%-99.8%.The homology of the available PCV3 full sequence gene was 98.6%-99.9%,and the homology of the available PCV3 ORF2 gene was 97.2%-99.4%.These results suggest that the PCV3 have the highly gene sequence homology.The all PCV3 strains can be divided into two subtypes,and these six strains in this study are distributed in two subtypes.In addition,PCVs ORF2 gene and its Cap protein were compared and analyzed.The results found that PCV1,PCV2 and PCV3 are relatively distant,although PCV1 and PCV2 are in the same branch,but the branch distance is far.PCV3 is in another big branch,and farther away from the other two types.The homology between PCV2 Cap protein and PCV3 Cap protein was only 26.5%-29.9%.By comparing the homology of PCVs Cap protein and comparing the amino acid sequence of PCVs Cap protein suggest that PCV2 and PCV3 have not cross-protective antigens.In this study,we analyzed the prevalence,molecular epidemiological characteristics and genetic evolution of PCV2 and PCV3 in healthy slaughter pigs in Guangxi,which provided reference for the prevention and control of PCV2 and PCV3 in Guangxi.