Identification and characterization of a second novel human erythrovirus variant, A6

Parvovirus B19 (B19), currently the only accepted member of the Erythrovirus genus, is the only parvovirus known to be pathogenic in humans. Recently a viral sequence, tentatively termed V9 which showed 11% variability from the published B19 sequences, was described from a patient with aplastic crisis. To search for additional parvovirus variants, we used the new NS1/7.5EC PCR assay whose primers were designed from a conserved region of the B19/V9 sequence and encompasses an MfeI restriction enzyme site that would allow differentiation between B19- and V9-like sequences. Screening of 225 serum and bone marrow samples and 62 plasma pools identified one new atypical parvovirus sequence, A6, from an anemic HIV-positive patient. A6 exhibited 88% similarity to B19 and 92% to V9, compared to >98% correspondence between reported B19 isolates. Based on the genome similarity to B19, an RT-PCR for A6 capsid transcripts was developed and used to test for A6 infectivity of UT7/Epo/S1 cells. Despite high viral titers, A6 viral transcripts were not detected. Thus, although the prevalence of B19 variants probably is low, the true clinical significance remains unknown. Current PCR analyses are unlikely to detect novel variants without the design of specific primers to the A6/V9/B19 common sequences.