| Since it was firstly discovered in 1998, porcine circovirus type 2 has spread worldwide and become one of the important pathogens that threatening the swine industry. PCV2 could disrupt host’s immune system and diminishing the number of the lymphocytes, which results in decreased immunity and sub-health state of the host. Under this state, the pigs become susceptible to other viral or bacterial pathogens, and even changes of the environment could also lead to diseases with various symptoms. Therefore, PCV2 has caused tremendous economic losses and it is still restricting the development of swine industry.In order to investigate the prevalence of PCV2 in Guangxi,284 lymph node and lung tissue samples were collected from different regions of Guangxi during August 2012 to January 2015. PCR method was used for virus detection in this study and the result showed that 50.7%(144/284) of the samples were detected positive for PCV2,which indicated that PCV2 has been widespread in Guangxi. The positive rates of different seasons were further analyzed,42.4% (38/85),91.5%(43/47),38.7%(43/111) and 53.7%(22/41) of the samples were showed PCV2 positive during spring, summer, autumn and winter respectively. The high positive rate (91.5%) during summer suggested that PCV2 was more prevalent in this season.To further understand the main genotypes of PCV2 in Guangxi. Parts of the positive samples were selected for complete genome amplification.45 PCV2 complete genome sequences were obtained in this study. Phylogenetic analysis showed that 39 of the strains belonged to PCV2b subtype and the rest 6 strains belonged to PCV2a subtype. This result indicated that PCV2b was the prevalent genotype in Guangxi. Moreover,2 subgroups could be divided in the PCV2 subtype; 14 and 25 strains belonged to PCV2b-lA/B, PCV2b-1C respectively. Compared to the previous results in our lab, we found that the prevalent PCV2 genotype was transforming from PCV2b-lA/B to PCV2b-1C subgroup. In this study,6 strains of PCV2a with China Jilin vaccine strain HM038034 and Hungary strain AY256459 was in the common branch of PCV2a. The 14 strains of PCV2b-lA/B with China Guangdong strain EF421971, China Anhui strain GU450327, China Zhejiang strain AY691169, China Henan strain FJ440338, China Liaoning strain HM776448 and strain China Beijing EF524530 are in the same small branch, but not in the small branches of China Zhejiang vaccine strain AY686764, China Shanxi vaccine strain HM641752 and Holland strain AF201897. In this study in 25 strains of PCV2b-1C,23 strains with China Heilongjiang strain HM038017, China Hubei vaccine strain FJ870971, China Shanghai vaccine strain AY686763, Hubei strain AY291317 and China Gansu FJ948168 are in the same branch. The other 2 strains PCV2b-1C with China Hubei strain AY035820, Indonesia strain EU302139 and the Vietnam strain JX506730 and JX099782 are in the same branch and are for the PCV2a and PCV2b-1C ORF2 recombinant strains.The complete genome sequence homology of the obtained 45 PCV2 strains was 94.2-99.9%.The homology ORF1 sequence was 96.5-100%. However, the ORF2 sequence homology was 88.9-99.9%. This result indicated that ORF2 showed higher variability than ORF1. The homolygy of the deduced amino acid sequence of the ORF1 and ORF2 were 97.5-100% and 87.2-100% respectively. Three heterogeneous domains (53-91 aa,121-151 aa and 185-215 aa) were found in the ORF2 deduced amino sequences, which covered 3 of the cap protein’s epitopes (69-83 aa,117-131 aa and 193-207 aa respectively). The different amino acid positions of PCV2 genotypes are main in 8,53,57,59,68, 77,86-81,121,130,131,133,134,151,169,185,187,190-191,206,210,215, 232,234. We can distinguish the type of PCV2a and PCV2b from D77, TNKISI86-91, P131, S133, I187, S190 and K232 and distinguish the subgroup of PCV2b-1A/B and PCV2b-1C from F8,153, N68, T121, N134, D210,1215 and K234.In order to isolate the prevalent PCV2 strain of Guangxi, a part of the 144 positive samples were inoculated in PK-15 following 10 blind passages. PCR method was used for virus identification and 3 PCV2 strains (GXGG-4-2013, GXNN-2-2014 and GXCZ-2014) were successfully isolated in this study. All of the 3 isolated PCV2 strains belonged to the PCV2b subtype and the GXGG-4-2013, GXNN-2-2014 belonged to the prevalent PCV2b-1C subgroup. Besides, the GXCZ-2014 belonged the subgroup of PCV2b-lA/B. After 80 passages of subculture, GXGG-4-2013 was conducted complete genome amplification for every ten generations. The result showed that the complete nucleotide sequence homology among every 10 generations was 99.5-100%, indicating its stable genetic characteristic during subculture.The result of this study is that analyzing the prevalence of PCV2 in parts of Guangxi and PCV2 molecular popular features, this can provide a theoretical reference for solving PCV2 prevention and control in Guangxi. Isolated three PCV2 can provide material for future study of biological characteristics of PCV2 isolates. |
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