Molluscum contagiosum virus expresses late genes in primary human fibroblasts but does not produce infectious progeny.

Molluscum contagiosum virus (MCV), a member of the family Poxviridae, can be isolated from skin-lesion material of patients with molluscum contagiosum infection. MCV replicates efficiently in human keratinocytes in vivo but viral replication has not been observed in vitro in cell or tissue culture systems. We investigated a variety of established cell lines for productive MCV infection and found that: (i) MCV induces a typical cytopathogenic effect (CPE) only in human primary fibroblast cells (MRC5 ATCC-CCL 171 and HEPM ATCC-CRL 1486) but not in permanent eucaryotic cell lines of human or simian origin; (ii) UV irradiated MCV virions and heat inactivated virions do not induce a CPE; (iii) decreasing amounts of MCV viral DNA are detectable in infected human embryonic fibroblasts for at least 14 days post infection (p.i.); (iv) MCV early mRNAs are detectable by RT-PCR between one and two hours p.i. and remain detectable upon passaging of the infected cells; (iv) transcripts of viral late genes (mc095L and mc106L) are detectable by RT-PCR from day 5 p.i.; (v) MCV viral antigens can be detected on the surface of infected cells using human and rabbit polyclonal antisera against MCV from 24 h p.i.; (vi) a CPE can not be observed if cell free supernatants or homogenizates of MCV infected cells are used to try passage of the virus onto uninfected human embryonic fibroblasts, indicating that infectious viral progeny is not produced. This is the first report demonstrating long time persistence of MCV viral DNA and expression of late proteins in an in vitro cell culture system.