Identification Of Porcine Circovirus 2(PCV2) Isolated From Jilin Province And Its Complete Genome Sequence Analysis

Porcine circovirus disease(PCVD) is caused by porcine circovirus type 2(PCV2), which is characterized with ematiation, anaemia, icterus, swelling of lymph nodes and diarrhea. PCV2, a member of Circoviridae family, is a small, non-enveloped, spherical single-stranded DNA virus. PCV2 mainly invades weaned piglets at the age of 8~12 weeks old, which caused the occurrence of postweaning multisystemic wasting syndrome(PMWS), porcine dermatitis and nephropathy syndrome(PDNS), porcine respiratory disease complex(PRDC), congenital tremors, proliferative necrotizing pneumonia and enteritis. PCV2 mainly invades the immune organs, resulting in the decrease or loss of immunity, which is easy to cause the occurrence of secondary infection or combined infection. Thus, the disease causes great economic loss to the worldwide pig industry.The natural PCV2 infection among pigs occurred in a farm with 170 pigs purchased before 15 days, including 80 adult pigs and 90 weaned piglets, in the Jilin province of China during December 2014. Of the 90 piglets, 40 developed the symptoms such as anorexia, dyspnea, slight increase in the body temperature, and so on. Then, the ill piglets appeared ematiation, diarrhea and skin becoming pale. In addition, dark red irregular papules were observed in the skin of hindlimb and perineal region. Finally, 30 piglets died due to exhaustion. The incidence of adult pigs was less, and no death occurred. The suspected porcine circovirus disease was confirmed by necropsy, histopathology observation, virus isolation and PCR detection, which was caused by porcine circovirus 2 infection. The lungs, spleen, lymph nodes and brains showed typical pathological changes by histopathological observation. The lung showed the changes of interstitial pneumonia, pneumonedema and bronchopneumonia. The interstitial pneumonia mainly occurred under the condition of viral infection, and lymphocytic infiltration was observed around bronchus. Thus, we concluded that the disease was caused by viral infection. The periarterial lymphatic sheath of the spleen increased thickness, which indicated that the immune reaction caused the pathogen was cellular immunity. Brain tissues appeared oedema and non-suppurative encephalitis. In addition, a porcine circovirus 2 strain(PCV2-JL/China/2015) was successfully isolated from spleens and lymph nodes by passaging in PK-15 cells. A pair of primers based on PCV2 was designed according to the published sequences in Gen Bank. The length of complete genome of PCV2-JL/China/2015 was 1767 bp by sequencing analysis. The results of the phylogenetic tree analysis indicated that there was a close genetic relationship between PCV2-JL/China/2015 and FJ594471-1C01 isolate from Changsha city.The above results will not only provide important reference data for the diagnosis and pathology study of PCVD, but also establish foundation for the study on the pathogenic mechanism of PCV2 and the development of vaccines.