The Investigate of Epidemiology and the Characteristics of Pcv2 Anhui Strains
|School||Anhui Agricultural University|
|Course||Preventive Veterinary Medicine|
|Keywords||porcine circovirus type 2 epidemiological investigation isolation and identification sequence analysis pathogenicity|
Pig circovirus disease is the general term for a series of pig diseases caused by porcine circovirus type 2 (PCV2)which mainly include postweaning multisystemic wasting syndrome (PMWS) and porcine dermatis and nephropathy syndrome (PDNS) and so on. PCV2 mainly against immune system leading to immune suppression and secondary infection of the pig. PCV2 provoked particular interest among world veterinary community, because the virus caused enormous losses direct and indirect on pig husbandry. In order to understand the prevalence and biological characteristics of PCV2, swine serum samples were collected from different areas in Anhui Province from 2008 to 2009. The pig serum samples were detected by ELISA to isolate and identify PCV2 epidemic strains. The ORF2s were sequenced and analyzed. Animal pathogenicity test was also conducted. This study is a scientific basis for understanding PCV2 infection and relevant characteristics of the local epidemic strains in Anhui. This study also provided scientific basis on choosing vaccine strain and theoretical basis for controlling of porcine circovirus.1. 468 serum samples from 14 areas in Anhui were detected for antibodies and nucleic acid against PCV2 by ELISA and PCR respectively. The average positive ratio of antibodies against PCV2 in 468 serum samples was 74.36%. The positive ratio of antibodies increased as pig growing up. The positive ratio of antibodies in southern Anhui was significantly higher than areas in north of the Huai River and areas between Yangtze River and Huai River. The compliance rate of PCR and ELISA was 99.37%. The infection of PCV2 existed widespreadly in pigs in Anhui. There was a co-existence phenomenon between viremia and antibody against PCV2.2. The disease tissues collected from suspected PMWS piglets in Feidong, Dingyuan, Baihu, Xuancheng and Feixi were conducted PCV2 detection using PCR amplification on specific DNA fragment of the virus. Positive samples were inoculated on PK-15 cells to isolate viruses. PCR, electron microscopy and indirect immunofluorescence test (IFA) were used to identify virus. Five PCV2 strains were confirmed by followed tests. Specific 630bp fragment was detected by PCR. 17nm virus particlesin diameter was seen by electron microscopy. The indirect immunofluorescence test showed specific fluorescence in the nucleus and cytoplasm. Then, the Five PCV2 isolates were named as FD0801, DY0801, BH0801, FX0901 and XCh0901.3. Nucleotide sequence form 1088 to 1718 (630bp) of ORF2 gene of five strains were compared with 27 reference strains registered in GenBank, the homology were 87.3% to 99.8%. The homology between five virus strains were 92.1% to 99.6%, The mutation of ORF2 gene was small after 30 passages. The phylogenetic tree showed the ORF2 gene nucleotide sequence of PCV2 is relatively stable. Its evolution is not showing obvious geographical correlation. The five virus strains may belong to PCV2b subtypes. The five isolated strains were conducted mouse pathogenicity test. The result of PCV2 antibody testing showed that the 0.8mL virus solution intraperitoneal injection combined with nose and mouth attacked can raise the infection probability of PCV2. The BH0801 strain was choosed according to organ lesions to conduct animal pathogenicity test. The serum of challenged pig showed antibody positive of PCV2, The organ lesions of poison attack pig were dark red patches in the lung, bleeding kidney surface, increased lymph nodules, and the appeared large number of multinucleated cells which were typical macro-and micro lesions of PCV2 infection. So, The BH0801 strain is expected to become the vaccine strain.