Molluscum contagiosum virus (MCV) infection causes the cutaneous lesions we call molluscum. Molluscum has become common in the last 30 years. Deciding the best course of therapy requires some fundamental understanding about how MCV relates to the following factors: epidemiology, childhood immunity and vaccination, clinical features, comorbidities, and quality of life. Treatment depends on many factors, including presence or absence of atopic dermatitis (AD) and/or pruritus, other symptoms, cosmetic location, and the child’s concern about the lesions. Therapeutics include destructive and immunologic therapies, the latter geared toward increasing immune response.
Epidemiology
Molluscum contagiosum virus is the solo member of the Molluscipoxvirus genus. Infection with MCV causes benign growth or tumors in the skin (ie, molluscum). The infection is slow to clear because the virus reduces the host’s immunity.1,2 Molluscum contagiosum virus is a double-stranded DNA virus that affects keratinocytes and genetically carries the tools for its own replication (ie, DNA-dependent RNA polymerase). The virus has a few subtypes—I/Ia, II, III, and IV—with MCV-I predominating in children and healthy humans and MCV-II in patients with human immunodeficiency virus.1,2 Typing is experimental and is not standardly performed in clinical practice. Molluscum contagiosum virus produces a variety of factors that block the host’s immune response, prolonging infection and preventing erythema and inflammatory response.3
Molluscum contagiosum virus is transmitted through skin-to-skin contact and fomites, including shared towels, bathtubs, spas, bath sponges, and pool equipment.2,4,5 Transmission from household contact and bathing together has been noted in pediatric patients with MCV. Based on the data it can be posited that the lesions are softer when wet and more readily release viral particles or fomites, and fomites may be left on surfaces, especially when a child is wet.6,7 Propensity for infection occurs in patients with AD and in immunosuppressed hosts, including children with human immunodeficiency virus and iatrogenic immunosuppression caused by chemotherapy.1,2,8 Contact sports can increase the risk of transmission, and outbreaks have occurred in pools,5,9 day-care facilities,10 and sports settings.11 Cases of congenital and vertically transmitted molluscum have been documented.12,13 Sexual transmission of MCV may be seen in adolescents who are sexually active. Although child-to-child transmission can occur in the groin area from shared equipment, transmission via sexual abuse also is possible.14 Bargman15 has mentioned the isolated genital location and lack of contact with other infected children as concerning features. Latency of new lesion appearance is anywhere from 1 to 50 days from the date of inoculation; therefore, new lesions are possible and expected even after therapy has been effective in eradicating visible lesions.10 Although clearance has been reported in 6 to 12 months, one pediatric study demonstrated 70% clearance by 1.5 years, suggesting the disease often is more prolonged.16 One-third of children will experience signs of inflammation, such as pruritus and/or erythema. Rare side effects include bacterial superinfection and hypersensitivity.2
One Dutch study from 1994, the largest database survey of children to date, cited a 17% cumulative incidence of molluscum in children by reviewing the data from 103 general practices.17 In a survey and review of molluscum by Braue et al,18 annual rates in populations vary but seem to maximize at approximately 6% to 7%. Sturt et al19 reviewed the prevalence in the indigenous West Sepik section of New Guinea and noted annual incidence rates of 6% in children younger than 10 years (range, 1.8%–10.9%). Epidemics occur and can produce large numbers of cases in a short time period.18 The cumulative prevalence in early childhood may be as high as 22%, as Sturt et al19 observed in children younger than 10 years.
Rising incidence and therefore rising lifetime prevalence appear to have been an issue in the last few decades. Data from the Indian Health Service have demonstrated increases in MCV in Native American children between 2001 and 2005.20 In adults, the data support a steady increase of molluscum from 1988-2007, with a 3-fold increase from 1988-1997 to 1998-2007 in a Spanish study.21 Better population-based data are needed.