Aetiology
The lesions are caused by the molluscum contagiosum virus (MCV), a member of the poxvirus family of large, complex, enveloped DNA viruses.
MCV is classified into two major genotypes: subtypes 1 and 2 (each of which includes several variants). Their relative abundance is known to vary geographically, although subtype 1 is the most prevalent globally. Clinically, infection caused by different subtypes is indistinguishable, but MCV subtype 2 infections have been described more frequently among adults, in genital lesions, and in people with HIV infection.[12][13]
MCV (irrespective of subtype) infects keratinocytes and mucosa, causing papular lesions. Primate species can be infected as well as humans.[1]
Pathophysiology
Molluscum contagiosum virus (MCV) infects the skin, causing lesion appearance within a few days to up to 6 weeks later. The virus induces abnormal keratinocyte growth with the appearance of heavily stained cells on haematoxylin and eosin staining. These abnormal keratinocytes are termed Henderson-Patterson bodies.
Despite the abnormal cellular growth, MCV does not cause dysplastic lesions. The duration of the lesions is variable, but in most cases, they are self-limiting in a period of 6 to 9 months. Lesions may, however, persist for 1 to 2 years in immunocompetent individuals, with more prolonged illness in immunocompromised patients. Clearance requires the appearance of anti-molluscum antibodies and cellular immunity.
The MCV encodes a number of virulence factors that prevent the natural immune process from effectively clearing the lesions.[1] MCV also encodes a glutathione peroxidase, which protects infected cells from oxidative damage by peroxides.
Transmission
Transmission is usually by direct physical contact. It has been reported in some contact sports, and also via swimming pools, and through the sharing of towels and sponges.[14][15]
In the context of adults, direct skin-to-skin contact during sexual intercourse is the most common mode of transmission.[5]
Classification
Classification of molluscum lesions
Molluscum contagiosum
Common molluscum are pearly papules with a central dell, usually over the chest wall and axillae in children, and in the groin and inner thighs in adults.
Giant molluscum
Lesions are usually smooth papules or nodules without central dell and are present in the inter-gluteal area or on the sole of the foot.
Inflamed molluscum
These lesions manifest erythema, swelling, and pruritus, typically as a marker of immune response to the lesions.
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