Genetic evolution of porcine circovirus in Hungary

Abstract

Porcine circoviruses type 2 (PCV2) are viruses of great economic importance as they are responsible for many different diseases called porcine circovirus associated diseases. Vaccination protocols are performed on pig herds all over the world in order to reduce the impact of the virus on the production. In fact the infection is often associated with reproduction failure in sows and post-weaning multisystemic wasting syndrome in piglets. During the last few years, cases of vaccination failure have been associated with a new strain of PCV2 called first PCV2d and then reclassified as mPCV2b. The commercial vaccine currently used is based on PCV2a and it is suppose to cover the animal against PCV2b also by cross protection. The mPCV2b strain contains a mutation in its Open Reading Frame 2 (ORF2) which encode for a larger capsid protein. In Hungary, cases of pigs presenting clinical signs which could correspond to PCV2 were reported. Semen samples from boars with Porcine reproductive and respiratory syndrome and tissue samples from pigs with haemorragic signs were sent for PCV2 detection and sequencing. We were able to amplify and sequence only 5 strains of PCV2b which were closely related to older viruses present in Serbia, Romania and Hungary. The viruses we couldn’t replicate seemed to present a different ORF2 as we were able to amplify and sequence the ORF1 but not the ORF2. The primers we used seemed to be inappropriate and were unable to attach on the ORF2 location. Those informations allowed us to conclude that PCV2b are still well represented in Hungary and that further study with different primers should be done to determine if the samples we couldn’t amplify are or aren’t mPCV2b and if the vaccination protocol based on PCV2a has to be improved.