B19 virus genome diversity: epidemiological and clinical correlations.

Genetic analysis of parvovirus B19 has been carried out mainly to establish a framework to track molecular epidemiology of the virus and to correlate sequence variability with different pathological and clinical manifestations of the virus. A good amount of information regarding B19 virus sequence variability is available, and presently there are about 400 sequence records deposited in the nucleotide database of NCBI. A few are almost complete genomic sequences, and these allow the construction of a global alignment framework. Many others are partial genomic sequences, limited to selected regions, and these allow comparison of a higher number of isolates from well-defined epidemiological settings and/or pathological conditions. Most studies showed that the genetic variability of B19 virus is low, that molecular epidemiology is possible only on a limited geographical and temporal setting, and that no clear correlations are present between genome sequence and distinctive pathological and clinical manifestations. More recently, several viral isolates have been identified that show remarkable sequence diversity with respect to reference sequences. The identification of variant isolates added to the knowledge of genetic diversity in this virus group and allowed the identification of three divergent genetic clusters, about 10% divergent from each other and still quite distinct from other parvoviruses, that can be thought of as different genotypes within the human erythrovirus group and that show clearly resolved phylogenetic relationship. These variant isolates pose interesting questions regarding the real extent of genetic variability in the human erythroviruses, the relevance of these viruses in terms of epidemiology and their possible implication in the pathogenesis of erythrovirus-related diseases.