Sometimes, discovery in biology is about discerning rules and sometimes it is about pursuing exceptions. In this spirit, Human Herpesvirus six (HHV-6), the etiologic agent of the common childhood illness roseola infantum, is shaping up to be an intriguing exception.
A recent post on Small Things Considered by Welkin Johnson, Assistant Professor of Microbiology and Molecular Genetics at Harvard Medical School, explores this subject:
"As every virologist knows, members of the Herpesviridae maintain their large double-stranded DNA genomes (typically 100-250kb) as autonomous, covalently closed circles (episomes) during latent infection of host tissues. Nevertheless, there is now convincing evidence that the HHV-6 genome can, at least on occasion, become integrated into host-cell chromosomes. Interestingly, the first hints that this could happen did not come from hypothesis-driven laboratory experiments, but from a handful of clinical case reports of individuals with exceptionally high levels of HHV-6 DNA in peripheral blood."
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