Demonstration of a unique viral structure: the molluscum viral colony sac.

Using scanning electron microscopy to study molluscum contagiosum lesions, it has been possible to demonstrate a unique, well defined sac enclosing the virion colony of each infected keratinocyte. This confirms the presence of a structure demonstrated over 50 years ago by micro-dissection, but ignored since it is not seen on either light or transmission electron microscopy. It is postulated that this sac, of unknown origin, favours replication of the virions by providing a site that is both anatomically and immunologically privileged. Such relatively unimpeded growth of the virions results in an enlarged cell in which the cytoplasm and nucleus are compressed into a thin outer shell. In the aggregate, this produces a tumour of virus-packed cells rather than a tumour composed of virus-induced cell hyperplasia.