Molluscum contagiosum (MC) is a viral infection of the skin or occasionally of the mucous membranes, sometimes called water warts. It is caused by a DNA poxvirus called the molluscum contagiosum virus (MCV). MCV has no nonhuman-animal reservoir (infecting only humans). There are four types of MCV, MCV-1 to -4; MCV-1 is the most prevalent and MCV-2 is seen usually in adults. The virus that causes molluscum is spread from person to person by touching the affected skin. The virus may also be spread by touching a surface with the virus on it, such as a towel, clothing, or toys. This common viral disease has a higher incidence in children, sexually active adults, and those who are immunodeficient, and the infection is most common in children aged one to ten years old. MC can affect any area of the skin but is most common on the trunk of the body, arms, groin, and legs. There is evidence that molluscum infections have globally been on the rise since 1966, but these infections are not routinely monitored because they are seldom serious and routinely disappear without treatment. Molluscum contagiosum is contagious until the bumps are gone. Some growths may remain for up to 4 years if not treated.
Signs and symptoms
Molluscum contagiosum lesions are flesh-colored, dome-shaped, and pearly in appearance. They are often 1â€"5 millimeters in diameter, with a dimpled center. They are generally not painful, but they may itch or become irritated. Picking or scratching the bumps may lead to further infection or scarring. In about 10% of the cases, eczema develops around the lesions. They may occasionally be complicated by secondary bacterial infections. The viral infection is limited to a localized area on the topmost layer of the epidermis. Once the virus-containing head of the lesion has been destroyed, the infection is gone. The central waxy core contains the virus. In a process called autoinoculation, the virus may spread to neighboring skin areas. Children are particularly susceptible to autoinoculation, and may have widespread clusters of lesions.
Individual molluscum lesions may go away on their own and are reported as lasting generally from 6 weeks, to 3 months. The lesions may propagate via autoinoculation so an outbreak generally lasts longer. Mean durations for an outbreak are variously reported from 8 months to about 18 months, but durations are reported as widely as 6 months to 5 years, lasting longer in immunosuppressed individuals.
Diagnosis
Diagnosis is made on the clinical appearance; the virus cannot routinely be cultured. The diagnosis can be confirmed by excisional biopsy.
Histologically, molluscum contagiosum is characterized by molluscume bodies in the epidermis above the stratum basale, which consist of large cells with:
- abundant granular eosinophilic cytoplasm (accumulated virions), and
- a small peripheral nucleus.
Treatments
Treatment options can often involve discomfort to the child so initial recommendations are often expectant management, simply waiting for the lesions to resolve spontaneously. Current treatment options are invasive, requiring tissue destruction and attendant discomfort. Currently there is no US licensed molluscum contagiosum vaccine; attempts have been made but it is difficult to instill a permanent immunity to the virus.
Treatments causing the skin on or near the lesions to rupture may spread the infection further, much the same as scratching does.
Bumps located in the genital area may be treated in an effort to prevent them from spreading. When treatment has resulted in elimination of all bumps, the infection has been effectively cured and will not reappear unless the person is reinfected.
Medications
Astringent chemicals applied to the surface of molluscum lesions to destroy successive layers of the skin include potassium hydrochloride, and cantharidin.
For mild cases, over-the-counter wart medicines, such as salicylic acid may or may not shorten infection duration. Daily topical application of tretinoin cream may also trigger resolution. These treatments require several months for the infection to clear, and are often associated with intense inflammation and possibly discomfort.
Imiquimod, a form of immunotherapy, had been proposed as a treatment for molluscum, based on promising results in small case series and clinical trials. However, two large randomized controlled trials, specifically requested by the U.S. Food and Drug Administration under the Best Pharmaceuticals for Children Act and completed in 2006, both demonstrated that imiquimod cream, applied three times per week, was after 18 weeks no more effective than placebo cream in treating molluscum in a total of 702 children aged 2â€"12 years old. In 2007 results from those trialsâ€"which have not been published or incorporated into the medical literatureâ€"were incorporated into FDA-approved prescribing information for imiquimod, which states: "Limitations of Use: Efficacy was not demonstrated for molluscum contagiosum in children aged 2â€"12." Imiquimod's FDA-approved prescribing information in 2007 was also updated to document concerning safety issues raised in the two large randomized controlled trials as well as a smaller pharmacokinetic study (also requested by FDA and subsequently published), including:
- Potential adverse effects of imiquimod use: "Similar to the studies conducted in adults, the most frequently reported adverse reaction from 2 studies in children with molluscum contagiosum was application site reaction. Adverse events which occurred more frequently in Aldara-treated subjects compared with vehicle-treated subjects generally resembled those seen in studies in indications approved for adults and also included otitis media (5% Aldara vs. 3% vehicle) and conjunctivitis (3% Aldara vs. 2% vehicle). Erythema was the most frequently reported local skin reaction. Severe local skin reactions reported by Aldara-treated subjects in the pediatric studies included erythema (28%), edema (8%), scabbing/crusting (5%), flaking/scaling (5%), erosion (2%) and weeping/exudate (2%)."
- Potential systemic absorption of imiquimod, with negative effects on white blood cell counts overall, and specifically neutrophil counts: "Among the 20 subjects with evaluable laboratory assessments, the median WBC count decreased by 1.4*109/L and the median absolute neutrophil count decreased by 1.42×109 Lâˆ'1."
There is no high quality evidence for cimetidine.
Surgery
Surgical treatments include cryosurgery, in which liquid nitrogen is used to freeze and destroy lesions, as well as scraping them off with a curette. Application of liquid nitrogen may cause burning or stinging at the treated site, which may persist for a few minutes after the treatment. Scarring or loss of color can complicate both these treatments. With liquid nitrogen, a blister may form at the treatment site, but it will slough off in two to four weeks. Although its use is banned by the FDA in the United States in its pure, undiluted form, the topical blistering agent cantharidin can be effective. Cryosurgery and curette scraping are not painless procedures. They may also leave scars and/or permanent white (depigmented) marks.
Laser
Pulsed dye laser therapy may be used for cases that are persistent and do not resolve following other measures. As of 2009 however there is no evidence for genital lesions.
Prognosis
Most cases of molluscum will clear up naturally within two years (usually within nine months). So long as the skin growths are present, there is a possibility of transmitting the infection to another person. When the growths are gone, the possibility for spreading the infection is ended.
Unlike herpes viruses, which can remain inactive in the body for months or years before reappearing, molluscum contagiosum does not remain in the body when the growths are gone from the skin and will not reappear on their own. However, there is no permanent immunity to the virus, and it is possible to become infected again upon exposure to an infected person.
One advantage of treatment is to hasten the resolution of the virus. This limits the size of the "pox" scar. If left untreated, molluscum growth can reach sizes as large as a pea or a marble. Spontaneous resolution of large lesions can occur, but will leave a larger, crater-like growth. As many treatment options are available, prognosis for minimal scarring is best if treatment is initiated while lesions are small.
Epidemiology
Approximately 122Â million people were affected worldwide by molluscum contagiosum as of 2010 (1.8% of the population).