[Porcine circovirus 2 (PCV2)--associations between sequence, function and virulence].

Presently, potential associations between PCV2 virulence and -sequence are discussed controversially. Practitioners are rattled, whether and to which extent spatio-temporal variations in PCV2 associated diseases (PCVD) on farms might be attributed to distinct PCV2 strains, differing in virulence, and if this factor should be taken into account regarding diagnosis and prophylaxis. The present paper provides a review on known and discussed functional elements of the PCV2 genome and their significance in pathogenesis is discussed. Furthermore, variability between and within PCV2 strains and discrepancy between the common phylogenetic considerations of the total genome or the open reading frame 2 (ORF 2) and single nucleotide variations are presented. Only incoherent associations between phylogeny and virulence determining sequences serve as an explanation for inconsistent results of different authors regarding sequence and virulence. The conclusion is that there are presently no molecular markers for PCV2 virulence. Thus, quantitative considerations still remain the major factor in diagnosis, prognosis, prophylaxis and control of PCVD.