Molluscum contagiosum virus

Molluscum contagiosum virus (MCV) is the causative agent of benign wart-like skin tumors limited to the human epidermis. This skin condition is known as molluscum contagiosum (MC) and is histologically classified as an acanthoma. MC has a worldwide distribution, is most common in preadolescent children, and occurs frequently in overcrowded populations with reduced hygenic standards. With a mean incidence of 0.1–5% MC is, after the eradication of smallpox, the only clinically relevant poxvirus infection of humans. MCV is a member of the family Poxviridae and the type species of the genus Molluscipoxvirus. It has a double-stranded DNA genome of 190 289 bp (GenBank accession U60315: MCV type 1/80) encoding 182 nonoverlapping open reading frames. About 20% of the gene complement shares homologies to other poxvirus proteins. Among the few unique MCV genes with known functions are an apoptosis inhibitor (vFLIP), an IL18-binding protein, a soluble IL8 antagonist, and an Hrs-binding protein. MCV can be readily diagnosed clinically but may be confused with early-stage orthopoxvirus and herpesvirus lesions or other hyperproliferative skin conditions. Other viral agents can be excluded by electron microscopy and polymerase chain reaction (PCR). Treatment consists of topical application of salicylic acid or removal by curettage

Stability of molluscum contagiosum virus DNA among 184 patient isolates: Evidence for variability of sequences in the terminal inverted repeats

The stability of the Molluscum contagiosum virus Type 1 genome (188 kbp) was studied in 184 DNA isolates from 131 patients. Variability of up to 1.5 kbp at both ends of the genome symmetrically was observed using restriction analysis of the DNA isolates and by Southern Blot experiments using cloned and labeled Hindlll terminal DNA fragments of MCV-1 prototype DNA. The variable sequences were mainly confined to the terminal fragments and parts of the MCV-1 terminal repeats. Labeled probes did not detect terminal sequences of MCV Type 2 under the applied stringency. A less marked instability of the central MCV-1 BamHI DNA fragment F was observed within the genome coordinates 0.431 to 0.454 mu. Reiteration of tandem repeats similar to those described for vaccinia virus might explain the variability of the terminal sequences and might be involved in viral replication

Poxvirus homologues of cellular genes

Over the course of time poxviruses have acquired or “captured” numerous homologues of cellular genes and incorporated them into their large DNA genomes. With more poxvirus genome sequencing data becoming available, the number of newly discovered poxviral cellular homologues is constantly increasing. A common feature of these genes is that they are nonessential for virus replication in vitro and they confer selective advantages in dealing with host cell differentiation and immune defense mechanisms in vivo. Poxviral cellular homologues are reviewed in this synopsis considering the specific viral habitats of different poxviruses and the immune defence capabilities of their respective hosts. Possible mechanisms of cellular gene acquisition by poxviruses as suggested by the analysis of mobile genetic elements in large DNA viruses are discussed. The investigation of poxvirus homologues of cellular genes is essential for our understanding of the mechanisms that regulate virus/host interactions on the cellular level and the host response against infection

Preparation and Use of Molluscum Contagiosum Virus from Human Tissue Biopsy Specimens

Molluscum contagiosum virus (MCV) lesions are limited to the human epidermis and can persist for months, showing only weak signs of inflammation. Because a culture system has not yet been created to replicate MCV, this chapter describes how the virus can be isolated from patient specimens. From this material, we describe how MCV is purified and used for infection studies, electron microscopy, viral DNA extraction, and analyses of early mRNA synthesized by in vitro transcription of permeabilized virions. The complete MCV-1 genome has been sequenced, and a redundant MCV genome fragment library of MCV type 1 (available from American Type Culture Collection [ATCC]) is useful for the cloning and study of individual MCV genes

Characterization of early gene transcripts of molluscum contagiosum virus

Molluscum contagiosum virus (MCV), a member of the family Poxviridae, replicates wellin vivobut cannot be propagated in cell culture. The coding capacity of the MCV genome was previously determined by DNA nucleotide sequence analysis. The objective of the present study was to establish experimental systems for the identification and characterization of early MCV gene transcripts. MCV mRNA was obtained in three ways: (1) MCV early mRNA was synthesizedin vitrousing permeabilized virions, (2) MCV mRNA was extracted from MCV-infected skin tissue, and (3) MCV mRNA was extracted from MCV-infected human embryonic fibroblasts. RNA/DNA hybridization experiments showed significant early transcriptional activity in two parts of the MCV genome. Transcripts of 11 early MCV genes located in these parts of the genome, including two subunits of the MCV DNA-dependent RNA polymerase (mc077R and mc079R), the MCV poly(A)+polymerase gene (mc076R), and the MCV MHC class I homolog (mc080R), were detected in reverse transcription-polymerase chain reaction experiments. Total RNA obtained from MCV-infected skin tissue was used to confirm these results. Three MCV early transcripts, mc002L, mc004.1L, and mc005L, produced distinct bands on rapid amplification of their 3′ ends (3′ RACE). The 5′ mapping of transcription start sites of MCV open reading frames (ORFs) mc002L, mc004.1L, mc005L, and mc148R revealed that the MCV RNA polymerase transcription start sites are consistently located between 11 and 13 nucleotides downstream of the early MCV consensus promoter signal. When cDNA from both 5′ and 3′ mapping experiments was analyzed, MCV ORFs mc004.1L and mc005L were found to be transcribed as a single bicistronic mRNA. The transcript from MCV ORF mc066L, encoding a glutathione peroxidase, was detected inin vitrosynthesized MCV mRNA as well as in total RNA from MCV-infected human embryonic fibroblasts and MCV-infected skin. This indicates that despite the lack of an early MCV consensus promoter signal immediately proximal to the start codon, this particular gene is transcribed early during MCV infection

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