Molluscum Contagiosum

This is a skin infection caused by a DNA pox virus that affects both children and adults. Transmission is usually by direct skin contact and has occurred in contact sports and by sharing baths, towels and gymnasium equipment. Outbreaks in schools are well recognised. Autoinoculation produces linear lesions.

Molluscum contagiosum is a viral skin infection caused by molluscum contagiosum virus (MCV), a DNA pox virus specifically a member of the the Poxviridae family.
There are four distinct subclasses of MCV, with MCV1 being the most common cause of molluscum contagiosum.

• There are no precise figures but molluscum contagiosum is common. The exact prevalence is uncertain. Many people never seek medical care and it is not a notifiable disease. Studies done often look at selected populations (for example attendees at genito-urinary medicine clinics or dermatology outpatient departments).
• A large UK general practice-based survey¹ reported:
  • The overall annual incidence of new cases of molluscum was 261/100,000.
  • The annual incidence of such cases in children aged under 15 years was 1265/100,000.
  • Over 80% of reported cases occurred in children aged under 15 years, with the maximum incidence in preschool children aged 1–4 years.
  • In a general practice population of 10,000 people, about 24 new cases of molluscum contagiosum would present each year.
• One Dutch study reported that one in six children have visited their doctor for the condition.²

Risk factors

• It occurs most often in children. Molluscum contagiosum has been reported in between 5.6% and 7.4% of primary school children.³
• It is commoner in hot climates and with poor hygiene.³ Childhood molluscum contagiosum is common in Papua New Guinea, Fiji, and certain parts of Africa.³
• Molluscum contagiosum occurs more commonly in people who are immunocompromised. For example:
  • In patients with HIV the prevalence of molluscum contagiosum is reported to be 5% and 33% (the prevalence increasing with decreasing CD4 counts).⁴
  • In patients who are on steroids or have lymphoproliferative disorders.
• However the vast majority of infected people have a competent immune system. It is usually acquired through direct contact.
• Molluscum contagiosum is said to occur more often in children with atopic eczema, although there is little evidence to support this.⁵
• It is almost exclusively a disease of humans and so there is neither a risk of children infecting pets nor pets infecting children.

Incubation period is between 2 and 7 weeks. Usually it is asymptomatic but there may be tenderness, pruritus and eczema around the lesions. They tend to spread more rapidly in atopic individuals or in skin conditions where the skin barrier is less effective. It is almost invariably confined to the skin but cases affecting the eyelids and conjunctiva have been reported. There is no pyrexia or malaise.

• Firm, smooth, umbilicated papules, usually 2 to 6 mm in diameter. Lesions bigger than 15mm have been described in AIDS.⁶
• They may be present in groups or spread over the skin and mucosal surfaces.
• They may be the colour of skin, white, translucent or slightly yellow.
• They may be single or up to 20 lesions but sometimes there are many more. They may become confluent and form a plaque.
• In children they are usually on the trunk or extremities. In adults they are often on the lower abdomen, inner thighs or genital region, suggesting sexual transmission. It is important to stress that the discovery of this distribution in children is not an indication of sexual abuse.
• Although rare, it has been reported on the buccal mucosa.
• In some conditions (for example sarcoidosis, lymphocytic leukemia, congenital immunodeficiency, selective immunoglobulin M deficiency, thymoma, prednisone and methotrexate therapy, AIDS, malignancy, atopic dermatitis), multiple widespread, persistent, and disfiguring lesions can occur (especially troublesome on the face but also involving the neck and trunk).³
• Any one lesion is likely to persist for about 2 months.

• Lichen Planus
• Dermatitis herpetiformis
• Basal cell carcinoma
• Keratoacanthoma
• Fibrous papule of the face
• Milia
• Spitz naevus
• Histiocytoma
• Other viral skin infections (including varicella, herpes virus infections and warts)

These are not usually required and diagnosis is made on clinical grounds based on the appearance of lesions. In exceptional circumstances when diagnosis is uncertain biopsy can be performed. Electron micrographs and fluorescent antibody techniques can be used. Serum antibody checks generally are not well standardised. It is best to discuss available diagnostic options with the local microbiology department. Referral to a genitourinary medicine clinic may be indicated if it is thought that it may have been transmitted through sexual contact.

• Parents often request treatment for their children and express concern about them spreading. However all techniques are a little painful and the management that is most popular with children is to await spontaneous resolution. Children do not have to be kept away from school.
• The disease is usually self limiting but there may be autoinfection or infection of others that means that definitive treatment is preferable. Each case should be individually assessed.⁷
• Active treatment may be more important if there is significant risk of spread to others or autoinoculation. This tends to apply to adults rather than children.
• In normal, healthy individuals, there are no controlled trials to compare treatments.
• There are a number of possible treatments:
  • A traditional one is to take a sharpened orange stick, dip it in phenol and then use it to burst the papules. The phenol may be unnecessary, especially as an alternative is simply to prick the papules with a sterile needle.
  • Another popular technique is the use of liquid nitrogen, as described in Minor Surgery.
  • In refractory cases (usually complicating immunodeficiency) the antiviral agent imiquimod may be beneficial.⁸
  • There are a host of other suggested treatments, both topical and systemic but most are unlicensed and in a self limiting condition are usually best avoided.³

• Discomfort and irritation
• Inflammation
• Secondary infections
• Eyelid lesions may be associated with follicular or papillary conjunctivitis.

It is a benign, self- limiting infection with an excellent prognosis.
The literature on molluscum contagiosum should be interpreted with care. Much research originates from secondary care on patients with impaired immunity.