Parvovirus B19 VP1/VP2

Parvovirus B19 (B19) was discovered serendipitously in 1974 and is the only member of the familyParvoviridae known to be pathogenic in humans. The virus is widespread, and manifestations of infection vary with the immunologic and hematologic status of the host. In healthy immunocompetent children, B19 is the cause of erythema infectiosum, an innocuous rash illness. Infection is occasionally, especially in adults, associated with an acute symmetric polyarthropathy that may mimic rheumatoid arthritis. The icosahedral capsid consists of two structural proteins, VP1 (83 kDa) and VP2 (58 kDa), which are identical except for 227 amino acids at the amino-terminal of the VP1-protein, the so-called VP1-unique region. Each capsid consists of a total of 60 capsomers: VP2 is the major capsid protein, and comprises approximately 95% of the total virus particle. VP1-proteins are incorporated into the capsid structure in a non-stochiometrical relation (based on antibody-binding analysis and X-ray structural analysis the VP1-unique region is assumed to be exposed at the surface of the virus particle. VP2 codons were found to be under purifying selection. In contrast VP1 codons in the unique part of the gene were found to be under diversifying selection. This diversifying selection is consistent with persistent infection as this part of the VP1 protein contains epitopes recognised by the immnune system.