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Abstract Pigs are often co-infected by different viral strains from the same virus. Up to now, there are few reports about co-existence of different porcine circovirus type 2 (PCV2) strains in China. The aim of this study was to evaluate it in Chinese swine herds. 118 PCV2 positive DNAs isolated from diseased pigs identified by classic PCR were re-detected using a modified differential PCR assay. The results indicated that co-existence rates of PCV2 were 32.2% (38/118) in diseased pigs and 0% (0/41) in asymptomatic pigs. Four PCV2 complete genomes were cloned from two co-infected samples and their nucleotide (nt) identities were 95%-97.3%. The phylogenetic analysis showed that four PCV2 strains were divided into different genotypes, PCV2a, PCV2b, PCV2d and PCV2e, respectively. In addition, co-existence were not detected in 41 serum samples from healthy pigs but PCV2 single infection (31.7%, 13/41) existed. These data revealed that the co-existence of different strains of PCV2 might contribute to the development of more severe clinical symptoms for pigs. This is the first report confirming the co-existence of different PCV2 strains in Chinese swine herds. Meanwhile, this study could help us to understand new infection and prevalence forms of PCV2 clinically.

[Objective] The existing situation and epidemic law of H1N1 and H3N2 subtype swine influenza viruses (SIV) in Guangxi was investigated in order to provide theoretical basis and original trace for monitoring and preventing SIV. [Method]The 11700 sera samples were collected from slaughterhouses, large-scale piggeries and individual farmers of 11 prefecture -level cities in Guangxi during 2009 -2013 and then detected by hemagglutination inhibition (HI) tests. The antibody positive rates of European avian H1N1 subtype (EA-H1N1 ) and novel human recombinant H3N2 subtype (Hu-H3N2) subtype strains viz., LB144, BB2, NNXD and JGB4 were analyzed to investigate their existing situations and epidemic laws. [Result]The EA-H1N1 subtype strain LB144 remained stable and became the predominant strain during 2009-2013, and its average antibody positive rate reached to 20.68%. Since the Hu -H3N2 subtype strain JGB4 began to prevail in 2010 and showed gradually spread tendency, and its average antibody positive rate was 19.96%. Baihai, Nanning, Yulin, Hezhou, Guilin, Guigang and Liuzhou in Guangxi suffered from multi-infection of Hu-H3N2 and EA-H1N1 subtype strains and their degrees of infection were more serious, while that of Baise, Hechi and Fangchenggang were relatively lower. Moreover, the fattening pig were the most susceptible to SIV, especially infecting BB2 and JGB4, and their antibody positive rates reached to 66.00% and 40.00%, respectively. The cross-infection positive rate between EA-H1N1 subtype strains (21.52% ) was lower than that between HuH3N2 subtype strains (27.45%). The cross-infection positive rate between BB2 and JGB4 strains was the highest (16.23%) among any two defferent subtype strains. The cross-infection positive rate among BB2, NNXD and JGB4 was the highest (11.60% ) among any three defferent strains. There was also cross-infection positive rate of 6.96% among four strains. [Conclusion]There exists widespread phenomenon of mixed infection among EA-H1N1 and Hu-H3N2 subtype strains in Guangxi swinery, especially more serious infection in some prefecture-level cities located in the border of two provinces. The fattening pig and weaning pig were more susceptible to SIV. Therefore, except the daily management of piglet and breeding pig, the outside stress on weaning pig should be reduced and the stocking density of fattening pig should be appropriately readjusted. These will be helpful to avoid generation of neotype recombinant SIV. [ABSTRACT FROM AUTHOR]