Isolation And Identification Of Porcine Circovirus Type 2 In Jiangsu Province And The Term Of Protection Induced By Chimeric PCV1-2 Attenuate Vaccine

Porcine circovirus type 2(PCV2)is the main cause of porcine circovirus associated diseases(PCVAD).Since it was first isolated in 1997,it has become the second immue-impaired agent to the pig industry.Another immue-impaired agent to the world's pig industry,porcine reproductive and respiratory syndrome virus(PRRSV),is a global epidemic that has caused huge economic losses to the pig industry worldwide.In about 2000,there were reports of PCVAD epidemics in China.Since then,the viral infection and PCVAD caused by PCV2 have been endemic and prevalent in China,and it is of great significance to prevent and control PCVAD in pigs in this country.This study provides a valuable reference for the epidemiology of porcine circovirus disease by isolating and identifying PCV2 strains from diseased pigs in some areas of Jiangsu province.The current prevention and control measures for PCVAD are based on massive vaccination.However,vaccination does not completely prevent the pigs from infection and transmission of PCV2 in the herd.At the same time,the current commercial vaccines are all inactivated,especially oil-emulsified inactivated vaccines with side-effects for vaccinated animals.The chimeric PCV1-2 live vaccine is easy to administ and requires relative low vaccination dose,implying low cost and favor to customers.The aim of this study is to immunize commercial pigs with the chimeric PCV1-2 live vaccine constructed in our laboratory,and to carry out PCV2 challenge on immunized pigs after 63 days post-vaccinnation so that the term of protection elicited by chimeric PCV1-2 live vaccine was evaluated.Based on the antibody determination,weight gain,viral load and histopathological examination of vaccinated and challenged pigs,the efficacy of live vaccine during the term of protection was explored.1 Isolation and identification of porcine circovirus type 2 strains in Jiangsu provinceThe lymphnode and lung tissues of pigs both from those submitted to the Yangzhou University Animal Hospital and an abattoir in Yangzhou were collected and detected by PCR test.Thereafter,porcine circovirus type 2 was isolated and identified from PCV2 positive tissue samples,consequently,11 PCV2 isolates were obtained and subjected to whole genome sequencing and genotyping.After sequencing the whole genome of 11 PCV2 isolates,it was found that 5 out of the 11 PCV2 isolates were PCV2b genotype,and the remaining 6 isolates belonged to PCV2d genotype.The genomic nucleotide sequences of the 11 isolates were aligned and the homology was 96.7-99.9%each other.Epidemiological investigations showed that PCV2b and PCV2d genotypes are prevalent in some area of Jiangsu province.The results provided PCVAD epidemiology with some data,and materials for studying the genetic variation and the evolution of PCV2 in Jiangsu province.2 Preliminary study on the term of protection induced by chimeric PCV1-2 attenuated vaccineIn this study,the chimeric PCV1-2 live vaccine constructed in our laboratory was used to immunize commercial pigs in a single dose,and the commercial vaccine administered pigs was applied as a control to evaluate the protection term induced by the live vaccine.Fourteen commercial pigs were randomly divided into four groups,each four pigs in the group 1,2 were adminstered with chimeric PCV1-2 live vaccine and the commercial inactivated vaccine,respectively.Pigs in group 1 were injected intramuscularly around neck with chimeric PCV1-2 live vaccine 2×105.3 TCID50/animal;pigs in group were immunized by the same way with the commercial inactivated vaccine 2 ml/pig;four pigs in group 3 were non-vaccinated but challenged as a challenge only group;and two pigs in the group were neither vaccinated nor challenged as a mock group.63 days post-vaccination,all the pigs except for those in mock group were challenged with PCV2b strain 0233 at a dose of 2×106.0 TCID50/animal.The serum of all pigs was collected weekly before and post-vaccination,the body weight was determined weekly pre-and post-challenge,and on 21 days post-challenge,all the test pigs were euthanized and anatomized,serum,lung,inguinal lymph nodes of all experimental pigs were collected respectively.The results of the study showed that PCV2 specific fluorescent antibody and neutralizing antibody were elicited in pigs vaccinated with either the commercial inactivated vaccine or chimeric PCV1-2 live vaccine,however,comparing with the commercial inactivated vaccine immunized animals,the live vaccine administered pigs seemed to produce above antibodies earlier,higher,and last longer.After challenge,PCV2 load in vaccinated pigs was reduced in serum,lymph node and lung compared with that of challenge only pigs.Histopathological results showed that the lungs and lymph nodes of the pigs in the challenge only group showed obvious lesions,while the pigs in the vaccinated and challenged group exhibited slight lesions.It can be drawn a conclusion that the PCV1-2 live vaccine can effectively protect the commercial pigs,judged by the elicited antibody,the reduced PCV2 loads,and the alleviated lesions in vaccinated pigs compared with the PCV2 challenge only pigs.