Podkliniczna i kliniczna cirkowiroza świń - zmienność wirusa PCV2

The paper is presenting basic data about circoviruses of swine and subclinical infection or disease they alternatively may cause. PCV1 is mentioned as being non pathogenic. Much more in detail is characterized the PCV2, being at present evaluated as one of the most important pathogenic viruses of swine. The virus is subdivided into genotypes of which PCV2a and PCV2b are the most pathogenic variants. The interaction between PCV2 and its natural hosts, domestic pig and wild boar, is a complex process. Two forms are differentiated: PCV2 – subclinical infection (PCV2-SI) and a disease with clinical symptoms, named nowadays PCV2 – systemic disease (PCV2-SD), replacing the earlier name: postweaning, multisystemic wasting syndrome (PMWS). However there is at present no satisfactory explanation why at the end of the 1990s or beginning of the XXI. century PCV2-SD from a mild and sporadic one changed into a severe epidemic disease. It is at present speculated that some role, contributing to this change may be played by the growing international trade of pigs belonging to susceptible swine genetic lines. The role of vaccination, contributing to selection of pathogenic variants of PCV2 could also be taken into account. An other factor could be co-infections, particularly with PRRSV, PPV and Mycoplasma hyopneumoniae. To some extend changes in management and husbandry could not be excluded. Nevertheless it is necessary to continue research in order to improve knowledge in this area.