Epidemiological Investigation And Molecular Characteristics Of Porcine Circovirus In Intensive Pig Farms In Guangdong Province

Porcine circovirus can be divided into Porcine circovirus type1(PCV1) and Porcine circovirus type2(PCV2), PCV2is known as the essentialetiological agent of some syndromes in pigs. PCV2is a hot research topic since itcaused PCVAD, however, PCV1has been less studied.In order to know the prevalence of Porcine circovirus (PCV) and Porcinereproductive and respiratory syndrome virus (PRRSV) in Guangdong province,807serum samples in different stages were collected from11pig farms in Guangdongprovince, the samples were detected of Porcine circovirus type1(PCV1) and Porcinecircovirus type2(PCV2) using nested-polymerase chain reactions (nPCR);655serumsamples of diseased pigs and152serum samples of healthy pigs were collected fromother pig farms from January on2010to February on2012, the samples were detectedPCV2using nPCR and detected PRRSV using one-step reverse transcriptasepolymerase chain reaction (RT-PCR). The results showed that all farms were positivefor PCV2but only5farms positive for PCV1,30.61%of sera were positive for PCV2,whereas only4.21%were positive for PCV1. Sows and nursery pigs older than7week-old showed the highest positive rates.59.1%of sera from diseased pigs showedpositive for PCV2and43.8%were positive for PRRSV,41.6%of PCV2positivesamples exhibited a concomitant infection with PRRSV. The diseased pigs showedhighest PCV2positive rates from October to December but lowest from January toMarch.37.5%of samples of healthy pigs were positive for PCV2while3.29%positive for PRRSV, there were no concurrent infection. The results showed that PCVespecially PCV2was popular in South China and shown a common concurrentinfection with PCV2and PRRSV. The PCV2positive rates has relation with seasons,cases of sows carrying PCV2were serious.In order to know the immune effect on antibody and initially evaluate theprotective efficiency of PCV2vaccine, learn the growth and decline of PCV2antibody,798serum samples in different stages were collected from Vaccination and non Vaccination pig farms in Guangdong province to detect PCV2antigen andantibody, completed sequences of some PCV2positive samples were amplified andsequenced. The results showed that100%of samples for boars and98.5%of samplesfor sows in Vaccination pig farms were positive for PCV2antibody. However,75%ofsamples for boars and91.3%of samples for sows in non Vaccination pig farms werepositive for PCV2antibody, the positive rate of Vaccination pig farms was higher thannon Vaccination pig farms, which showed that the PCV2antibody was elicited afterimmunization of PCV2vaccine. The results also showed that8.61%of samples forsows in Vaccination pig farms were positive for PCV2,24.3%of samples for sows innon Vaccination pig farms were positive for PCV2and PCV2infection rate had asignificantly decreased tendency in Vaccination pig farms. The PCV2positive rateswere not corresponded with PCV2antibody positive rates by comparing their rates ofprepubertal gilts, sows and boars respectively, and the antibody positive rates werefurther high than PCV2positive rates which showed that the results of PCV2antibodypositive rates can not prove the PCV2positive rates. The PCV2and PCV2antibodypositive rates of piglets suggested regular changes with the weeks of age increasing.There are two peaks for PCV2antibody from1week-old to3week-old and from6week-old to10week-old, PCV2positive rate was gradually increasing after6week-old. The PCV2positive rate of Vaccination pig farms were significantly lowerthan non Vaccination pig farms, the result showed that if sows were vaccinated, thepiglets would be protected to a certain degree. The complete genomes of PCV2isolates from Vaccination pig farms and non Vaccination pig farms showed highhomologies with PCV2isolate (AF055393) from French and PCV2isolate(DQ220730) from Canada, all PCV2isolates from this study showed closerrelationship to PCV2isolates from China according to the phylogenetic tree.PCV2can be subdivided into subgroups according to the phylogenetic tree. Theprocedure for typing PCV2was complicated and high cost. In order to develop PCRmethod to detect subgroup of PCV2,3primers were designed to amplify PCV2a andPCV2b according to the features of their genome sequences. The results showed themethod was specific and sensitive for PCV2a and PCV2b, it suited for detection ofPCV2a and PCV2b.441serum samples were collected from different regions inGuangdong province, and the detection results revealed that the PCV2positive ratewas31.5%in healthy herds and42.1%in diseased herds. PCV2b was the prevalentgenotype and only a small amount of PCV2a infection was present, the results showed that PCV2b has become the epidemic genotype in Guangdong province.In order to know the epidemic strain and the variation of PCV2in Guangdongprovince, a total of23serum samples from suspected PCVAD pigs collected from2010to2012in different regions of Guangdong province were used to isolate PCV2.The isolated virus were detected using nPCR and indirect immunofluorescence assay,and PCV2completed sequences were amplificated by PCR.21genomes of thesePCV2isolates showed1767bp in length, however,2of them were1766bp in length.The homologies of these strains were94.5%to99%, and the homologies of thesestrains with other strains in GenBank were94.2%to99%. All PCV2isolates in thisstudy showed closer relationship with PCV2isolates in domestic according to thephylogenetic tree, but there also have some differences among them. The epidemicstrain was different at the same period or different periods in the same pig farm.