The only virus in the genus Mulluscipoxvirus is the causative agent of a specifically human disease known as molluscum contagiosum. Below is a summary of some of the key features of molluscum contagiosum.
Molluscum contagiosum occurs worldwide, but is much more frequent in certain areas like Zaire and Papua New Guinea. It is seen most commonly in children, but it may be found in persons of all ages. The virus is transmitted by direct bodily contact, through minor abrasions, or indirectly via fomites. Among young adults, it is usually a sexually transmitted disease. Since 1980, there have been reports in the U.S. of greater severity of molluscum contagiosum in patients infected with HIV.
There are three viral subtypes: MCV I, MCV II, and MCVIII. MCV I is the most common of the three.
The incubation period for this virus, as determined by human volunteers who underwent inoculation, ranges from 14 to 50 days.
Clinical Features and Outcome
Infection with molluscum contagiosum virus gives rise to pearly, flesh colored, raised nodules found only in the epidermal layer of the skin. The nodules usually measure 2-5 mm in diameter. The lesions may be found anywhere on the body, but rarely occur on the palms or soles. At the top of each lesion, there is usually an opening through which a distinctive small, white cone can be seen. These lesions are usually painless.
The disease is chronic, with lesions persisting for months and in some cases, years. Recovery usually occurs spontaneously, or following bacterial infection. However, recurrences may occur rather frequently.
Pathogenesis and Pathology
The typical molluscum contagiosum lesion consists of a localized mass of hypertrophied epidermis, which extends down into the dermis without injury to the basement membrane. It projects above the adjacent skin as a visible tumor. There are pathologic changes in the nuclei and cytoplasm, with large hyaline acidophilic granular masses, known as mollsucum bodies, filling the cytoplasm and pushing the nucleus to the edge of the cell.
The center of the lesion consists of degenerating epidermal cells with inclusion bodies and keratin. There is very little inflammatory reaction unless a secondary bacterial infection has occurred.
Infection with molluscum contagiosum produces little immunity, with reinfection being relatively common among immunocompromised individuals.
Treatment and Prevention
There is no specific treatment for molluscum contagiosum, but the lesion core can be removed surgically and the lesion can be treated by cryotherapy. Lesions in children tend to disappear as they grow older. However, as previously mentioned, the lesions may recur spontaneously. In AIDS patients, new lesions may appear in the anogenital area and on the head and neck.
Avoiding direct contact with infected persons and use of standard protection against sexually transmitted diseases are two means of preventing infection by molluscum contagiosum virus. Communal swimming pools and gymnasiums may be a source of infection, and thus precautionary measures, such as routine disinfection of pools with chlorine and thorough washing of towels, can prevent transmission.