Molluscum contagiosum is a poxvirus that causes a chronic localized infection, consisting of flesh-colored, dome-shaped papules on the skin of an infected individual. The epidemiology, clinical features, diagnosis, and management of molluscum contagiosum will be reviewed here.
Molluscum contagiosum is a member of the poxvirus family but is in a different genus from the orthopoxviruses (variola, vaccinia, and monkeypox viruses) discussed separately (see "The epidemiology, pathogenesis, and clinical manifestations of smallpox" and "Vaccinia virus as the smallpox vaccine" and "Monkeypox"). Molluscum contagiosum causes a chronic localized infection with small papules on the skin of an infected individual in contrast to the acute, sometimes fatal, disease induced by smallpox. Similar to the virus that causes smallpox, the only known host is humans.
Information about molluscum contagiosum at the molecular level has been hampered by the inability to grow the virus in standard cell culture or in an animal model of infection. While there are reports of some success in growth using human foreskin xenograft fragments , a major advance in understanding the biology of the virus came when the entire 190,000 base pair genome of the molluscum contagiosum virus was sequenced [2,3].
Like variola and vaccinia viruses, molluscum contagiosum replicates in the cytoplasm of cells, and thus, it is not surprising that more than one-half of the genes are similar to those found in variola and vaccinia viruses. However, since the diseases induced are quite different , it also is not surprising that many genes found in variola and vaccinia are not present in the molluscum contagiosum genome [2,3]. Molluscum contagiosum contains many unique genes that encode proteins responsible for novel host defense mechanisms; these mechanisms inhibit the host inflammatory and immune responses to the infection [5-9].
Molluscum contagiosum infection has been reported worldwide. Although four distinct genotypes have been identified, genotype 1 predominates and represents 90 percent of cases in the United States . A population-based Australian seroepidemiology study in 357 people revealed an overall seropositivity rate of 23 percent . The data also indicated that very mild or subclinical cases may be more common in the general community than previously suspected.