Excerpt from Molluscum Contagiosum

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Background

Molluscum contagiosum is a benign viral disease of the skin that is caused by a member of the poxvirus group, molluscum contagiosum virus (MCV). The virus is one of the largest that causes human disease, measuring 240-320 nm in diameter.

Bateman first described the disease in 1817. The term molluscum was used to describe the pedunculated appearance, and the term contagiosum was used to connote that the disease is transmissible.

Interestingly, the idea of an infectious etiology arose after successful transmission occurred in humans who were inoculated with the materials contained within the lesions. Goodpasture first noted the microscopic similarities that exist between molluscum contagiosum and vaccinia (ie, smallpox).

Pathophysiology

This virus is known to infect only the epidermis. The initial infection seems to occur in the basal layer, and it may be accompanied by a latent period of as long as 6 months. The incubation period is usually shorter (ie, 2-7 wk). This is suggested by the fact that while viral particles are noted in the basal layer, viral DNA replication and the formation of new viral particles do not occur until the spindle and granular layers of the epidermis are involved.

Occasionally, the lesions can progress beyond the local cellular proliferation, and they can become inflamed with the attendant edema, increased vascularity, and infiltration by neutrophils, lymphocytes, and monocytes. Usually, this only occurs if there is a secondary bacterial infection or if rupture into the dermis occurs.

Cell-mediated immunity is thought to be important in modulating and controlling the infection because children and HIV-infected patients are noted to have more widespread and persistent lesions. The incidence and severity of molluscum in HIV-positive and AIDS patients appears to be inversely related to the CD4 count. More severe cases also have been noted in patients who are receiving prednisone and methotrexate. The virus infrequently induces antibody formation; therefore, it is not strongly immunogenic, and reinfection is common.

Frequency

United States

Molluscum contagiosum is a common infection throughout the United States. It accounts for approximately 1% of all diagnoses of skin disorders. The exact incidence in the United States is unknown. Higher incidence in children with eczema as well as in immunocompromised individuals has been documented.

The infection is transmitted by close physical contact, fomites, and autoinoculation (whereby the patient manually spreads the infection from one location to another, by touching or scratching). Crowded living conditions, use of public pools, and sharing of clothes and towels by infected persons have all been implicated in the spread of the virus.

International

Molluscum contagiosum has an incidence of up to 4.5% in some population groups. During a regional outbreak in East Africa, it was estimated that 17% of a village's general population and up to 52% of children older than 2 years developed lesions. Poverty, overcrowding, and poor hygiene play key roles in the propagation of this disease. There appears to be a greater incidence of molluscum in tropical areas, although fairly high incidences have been documented in northern European countries as well.

An Australian study found anti-MCV antibodies in 39% of adults older than 50 years, demonstrating exposure to be very common.

Mortality/Morbidity

Molluscum contagiosum is a benign process; therefore, morbidity and mortality are limited.

• For the most part, morbidity is due to adverse cosmetic results, which usually resolve, without scarring.
• The lesions can undergo secondary bacterial infection, but morbidity is limited when appropriate antibiotics are used.
• Morbidity is greater in immunocompromised and immunodeficient patients since they tend to have a greater number of lesions and more widespread infection, resulting in a greater likelihood of superinfection.
• Despite the rather benign, self-limited course, parents of affected children perceive molluscum to be a significant problem. They cite concerns with scarring, pain, itching, painful treatment, and the chance of spread to peers.

Race

• There is no well-documented predilection for infection among any racial group.
• In one longitudinal study in the United States, 2-4 times as many cases occurred among whites than among other racial groups. This study took place from 1977-1981, and it is unclear if the noted difference was secondary to the differences in accessibility to medical care or other socioeconomic factors.

Sex

Studies do not demonstrate any definite difference in incidence between the sexes.

Age

Infection with molluscum contagiosum occurs in all age groups, and prevalence seems to be increasing.

• The greatest incidence is in children younger than 5 years. This is thought to result from casual contact and autoinoculation.
• Another smaller spike of incidence occurs in young adults, resulting from propagation through sexual contact.
• Infection in infants is rare, perhaps because of the persistence of maternal antibodies.

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