Genus Molluscipoxvirus

Abstract

Molluscum contagiosum (MC) is a common wart-like skin infection mainly seen in children and caused by Molluscum contagiosum virus (MCV). The typical poxvirus particle morphology and genome organization of MCV led to its classification as a member of the family Poxviridae where it is the sole member of the genus Molluscipoxvirus. The genome of MCV type 1 (MCV 1/80) has been completely sequenced (GenBank accession U60315). Of 182 hypothetical MCV open reading frames (> 45 amino acids) only 35 have a significant homology to coding sequences of other poxviruses. Unique MCV genes include mc159, an apoptosis inhibitor (vFLIP), mc054, a viral IL-18 binding protein, mc148, a soluble IL-8 antagonist, and mc162, a Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) binding protein. MCV does not encode an epidermal growth factor (EGF) homolog. MCV shares a number of genes only with para- and avipoxviruses and stands out as phylogenetically distinct from all other poxviruses. This is reflected in a number of unique biological characteristics that set MCV apart from other poxviruses: MCV replication in vivo is limited to differentiating keratinocytes of the spineous layer of the human epidermis. MCV induces an enhanced rate of mitosis in keratinocytes, possibly by way of EGF receptor up-regulation, and interferes with the normal epidermal cell differentiation program. The lack of local inflammation gives typical MCV lesions a pearly bland appearance. MC infection can persist in human skin for years. An inflammatory reaction, spontaneous or induced by trauma, frequently leads to the sudden and complete disappearance of MCV lesions. The local, subacute and proliferative nature of the MC infection puts MCV close to a group of animal poxviruses causing slow growing skin tumors. MCV replicates inefficiently in skin xenotranplants to immunodeficient mice. There is currently no cell- or tissue culture system that supports replication of MCV in vitro.