Molluscum contagiosum (MC) is a viral infection of the skin or occasionally of the mucous membranes. MC has no animal reservoir, infecting only humans, as did smallpox. However, there are different pox viruses that infect many other mammals. The infecting human MC virus is a DNA poxvirus called the molluscum contagiosum virus (MCV). There are four types of MCV, MCV-1 to -4; MCV-1 is the most prevalent and MCV-2 is seen usually in adults and often sexually transmitted. About one in six young people are infected at some time with MC. 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 body, arms, and legs. It is spread through direct contact or shared items such as clothing or towels.
The virus commonly spreads through skin-to-skin contact. This includes sexual contact or touching or scratching the bumps and then touching the skin. Handling objects that have the virus on them, such as a towel, can also result in infection. The virus can spread from one part of the body to another or to other people. The virus can be spread among children at day care or at school. Molluscum contagiosum is contagious until the bumps are gone-which, if untreated, may be up to 6 months or longer.
The time from infection to the appearance of lesions ranges from 2 week to 6 months, with an average incubation period of 6 weeks. Diagnosis is made on the clinical appearance; the virus cannot routinely be cultured, this can be done by popping with a needle but it must be done regularly to prevent multipying.
Molluscum contagiosum lesions are flesh-colored, dome-shaped, and pearly in appearance. They are often 1–5 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. In some cases the dimpled section may bleed once or twice.
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 auto-inoculation, and may have widespread clusters of lesions.
Individual molluscum lesions may go away on their own and are reported as lasting generally from 6 to 8 weeks, to 2 or 3 months. However via autoinoculation, the disease may propagate and so an outbreak generally lasts longer with mean durations variously reported as 8 months, to about 18 months and with a range of durations from 6 months to 5 years.
Treatment is often unnecessary depending on the location and number of lesions, and no single approach has been convincingly shown to be effective. Nonetheless, treatment may be sought after for the following reasons:Top ^
Many health professionals recommend treating bumps located in the genital area to prevent them from spreading. The virus lives only in the skin and once the growths are gone, the virus is gone and cannot be spread to others. Molluscum contagiosum is not like herpes viruses, which can remain dormant in the body for long periods and then reappear. Thus, when treatment has resulted in elimination of all bumps, the infection has been effectively cured and will not reappear unless the patient is reinfected. In practice, it may not be easy to see all of the molluscum contagiosum bumps. Even though they appear to be gone, there may be some that were overlooked. If this is the case, one may develop new bumps by autoinoculation, despite their apparent absence.
Cryotherapy involves killing infected cells by “freezing” them with a pressurized liquid spray, usually liquid nitrogen or nitrous oxide. The procedure is relatively painless and can be performed by any health professional, including nurse practitioner or physician assistant. The infected cells may fall off immediately or fade over several days.
In a small randomized controlled trial twice daily application of 10% benzoyl peroxide cream for 4 weeks was found to be more effective than tretinoin 0.05% cream; after 6 weeks 92% of the benzoyl peroxide group were lesion-free, compared with 45% of the tretinoin group (p = 0,02)
Cantharidin is a chemical found naturally in many members of the beetle family Meloidae which causes dermal blistering. Not FDA approved but available through Canada or select US compounding pharmacy. It is a great method for treatment of small children, as it is not painful on application. Usually can not be used near the eyes or in uncooperative children, as the chemical is caustic if scratched and rubbed on the eyes. Usually applied with a wooden applicator like the sharp end of a wooden Qtip. Some advocate leaving it on unoccluded. Some advocate covering it with tape for 1 to 8 hours.
Another essential oil, tea tree oil is reported to at least reduce growth and spread of lesions when used in dilute form. Tea tree oil may cause contact dermatitis to those with sensitive skin, although less often in dilute form.
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 (“Retin-A 0.025%”) may also trigger resolution. These treatments require several months for the infection to clear, and are often associated with intense inflammation and possibly discomfort.
Doctors occasionally prescribe Imiquimod, the optimum schedule for its use has yet to be established. Imiquimod is a form of immunotherapy. Immunotherapy triggers your immune system to fight the virus causing the skin growth. Imiquimod is applied 3 times per week, left on the skin for 6 to 10 hours, and washed off. A course may last from 4 to 16 weeks. Small studies have indicated that it is successful about 80% of the time. Another dose regimen: apply imiquimod three times daily for 5 consecutive days each week. This is not FDA-approved treatment for molluscum contagiosum.
Cimetidine (however, double blind placebo studies seem to refute this), Griseofulvin (single case, anecdotal evidence) and Methisazone have seen some use.
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. It should be noted that cryosurgery and curette scraping are not painless procedures. They may also leave scars and/or permanent white (depigmented) marks.
Pulsed dye laser therapy for molluscum contagiosum may be the treatment of choice for multiple lesions in a cooperative patient (Dermatologic Surgery, 1998). The use of pulsed dye laser for the treatment of MC has been documented with excellent results. The therapy was well tolerated, without scars or pigment anomalies. The lesions resolved without scarring at 2 weeks. Studies show 96%–99% of the lesions resolved with one treatment. The pulsed dye laser is quick and efficient, but its expense makes it less cost effective than other options. Also, not all dermatology offices have this 585nm laser. It is important to remember that removal of the visible bumps does not cure the disease. The virus is in the skin and new bumps often appear over the course of a year until the body mounts an effective immune response to the virus. Thus any surgical treatment may require it to be repeated each time new crops of lesions appear.
Application of duct tape over lesions until they begin to crust over and heal is well tolerated, has been effective, and can be implemented at home with readily available materials. Tape is cut to the size of lesions and applied after washing or when previously applied tape falls off. This treatment for molluscum was motivated by success with treating warts similarly. The conclusions of a controlled study were that duct tape occlusion therapy was significantly more effective than cryotherapy for treatment of the common wart.
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, like the common cold, there is no permanent immunity to the virus, and it is possible to become infected again in the future upon exposure to an infected person.