Molluscum contagiosum virus
Molluscum contagiosum virus (MCV) is a DNA poxvirus that causes the human skin infection molluscum contagiosum.[1] Molluscum contagiosum affects about 200,000 people a year, about 1% of all diagnosed skin diseases. Diagnosis is based on the size and shape of the skin lesions and can be confirmed with a biopsy, as the virus cannot be routinely cultured.[2] Molluscum contagiosum virus is the only species in the genus Molluscipoxvirus.[3] MCV is a member of the subfamily Chordopoxvirinae of family Poxviridae.[4] Other commonly known viruses that reside in the subfamily Chordopoxvirinae are variola virus (cause of smallpox) and monkeypox virus.[3]
The poxvirus family uniquely contains both non-enveloped particles (mature virions), and enveloped particles (extracellular virions).[5] The structure of the virions is consistent with that of others in the poxvirus family: they are composed of a nucleocapsid, core envelope, lateral body, and an extracellular envelope. Like other poxviruses, MCV is a DNA virus that replicates in the cytoplasm instead of the nucleus. Because of this, the virus must bring all necessary enzymes for replication with it or encode the enzymes in its genome.
The Molluscum contagiosum virus virion is described as oval-shaped and has the dimension of approximately 320 nm × 250 nm × 200 nm. The virus has two distinct infectious particles called the mature virion (MV) and the enveloped virion (EV), which differ in that the EV contains a second outer cellular membrane. Poxviridae is the only virus family that contains both enveloped and non-enveloped infectious particles. Other structures of the EV and MV virion include the nucleocapsid, core wall, and two lateral bodies.[6] Before the virion is released into the cytosol, the lateral bodies are associated with the virion core through boding interactions. However, during virion release into the cytoplasm, the virion core wall expands and forces the lateral bodies to dissociate. The lateral bodies function to transport one or more vital virion proteins needed for genome replication or expression.[7]
The genome consists of a linear double stranded DNA molecule that is approximately 190 kilobases in length. The genome is unique in that the two ends of the double stranded DNA sequence are inverted repeats of each other. This inverted terminal sequence is 4.7 kilobases in length, but can vary from 0.7-12 kilobases among poxviruses. There are 182 genes that are encoded by Molluscum contagiosum virus. Over 100 of these genes are conserved in other viruses from the poxvirus family, such as Variola virus and Vaccinia virus. The inverted terminal sequence of MCV differs from the sequences of others in the poxvirus family because it contains genus-specific host response evasion genes. The genome contains 64% GC bases, and thus encodes a lesser amount of the stop codons UAA, UGA, and UAG compared to other poxviruses. Further gene analysis has shown the MCV genome contains many long and overlapping open reading frames.[8]
