Detection Of Porcine Circovirus Type3 In 14 Provinces Of China By PCR And Full-genome Sequencing And Analysis Of Some Positive Samples

Porcine circovirus 3(PCV3)is a new emerging porcine circovirus which was firstly reported in the US.Since 2016,it has been reported in China,South Korea,Poland,Italy,Brazil,Germany,Thailand and other countries.PCV3 could be probably associated with various clinical symptoms,such as postweaning multisystemic wasting syndrome(PMWS),porcine dematitis and nephropathy syndrome(PDNS),reproductive failure,porcine respiratory disease complex(PRDC)and congenital tremors(CT).PCV3 has been reported in many provinces in our country.China,as a big pig-raising country,we need to pay enough attention to the prevalence of PCV3 and to carry out a more extensive and in-depth study.A total of 156 clinical samples including aborted fetuses and dead piglets from14 provinces(municipalities)were collected and tested by conventional PCR method.Among the pigs of different ages,the positive rate of aborted fetus was 28.0%(28/100),1~4 weeks old piglets were 22.2%(8/36),and 20.0%(4/20)for 5~8 weeks old pigs.The highest positive rate of tissues and organs was lymph nodes,which was17.6%(19/108),followed by lung 17.0%(18/106),tonsil 14.9%(13/97),kidney11.6%(11/95),brain 8.5%(7/82),spleen 6.8%(6/88),heart 6.5%(6/93),liver 5.2%(5/96).The above results suggested that PCV3 has widely spread in some regions of China.PCV3 was found to co-infect with a various of pathogens,which make a great challenge for the prevention and control of this disease.PCV2?PRRSV and PRV were detected in PCV3-positive pigs(a total of 40 samples).The results showed that the co-infection rate of PCV3 with PCV2 was 32.5%,with PRRSV was 22.5%,with PRV was 7.5%;and with PCV3,PCV2,PRV and PRRSV was 2.5%.In this study,the PCV3 full-genome was amplified by PCR in sections,and theamplified fragment was cloned into the vector.After correct identification,followed by sequencing,splicing and comparing,four PCV3 genomes were obtained.Genetic phylogenetic analysis and nucleotide homology analysis showed that there was a certain genetic relationship between the four strains: the nucleotide homology among the four strains was 99.1%~99.3%.The nucleotide homology of the four strains with11 strains in China is 98.7%~99.6% and with 12 strains abroad is 98.5%~99.5%.