MOLLUSCUM CONTAGIOSUM

           The disease molluscum contagiosum is caused by a poxvirus by the same name, molluscum contagiosum. The disease is a benign tumor of mucocutaneous sites. The viral etiology of this condition was discovered by Juliusburg in 1905.

 Etiology:

          The virus is placed as the only member of the genus Molluscipoxvirus. The genome is a linear double-stranded DNA. On the basis of profiles created by restriction endonucleases, it has been divided into four subtypes, I, II, III and IV.

 Pathogenesis:

          Molluscum contagiosum is a communicable disease, which is transmitted through direct (including sexual) contact with infected individuals. Swimming pools, communal bathing facilities, shared towels and close contact between children at play are the usual sources of infection. There are no animal host and humans are the only hosts for this virus. It has been reported to occur in all age groups, but is more common in children and sexually active adults. People with multiple sex partners and those indulging in unprotected sex are more at risk.

           Incubation period can vary from two weeks to six months. Epidermal keratinocytes are the target cells. Viral replication occurs in the cytoplasm of the affected cells and produce large eosinophilic inclusion bodies called molluscum bodies or Henderson-Paterson bodies. Inclusion bodies are more evident in stratum granulosum and stratum corneum of the epidermis. Hyperproliferation of the epidermis also occurs because of a doubling in the rate of cellular division of the epidermal basal layer. The onset is gradual. The lesions begin as a group of minute papules in one to two areas. Individual lesions are discrete, smooth, pearly to flesh-coloured dome-shaped papules with central umbilication. Lesions may be few or numerous, depending on the immunological status of the host.

          In children lesions usually 1-2 mm in diameter and number fewer than 20 and are generally distributed on the trunk, arms, legs, and face. In immunocompetent adults lesions are usually found on the genitalia, lower abdomen, inner upper thighs, and/or buttocks. The lesions may persist for 6-9 months but sometimes lesions may persist up to 5 years.      In immunocompromised individuals lesions are far too many, are larger (>2cm) in size and may persist for more than 5 years. Molluscum contagiosum is rarely found in the oral mucosa and conjunctiva. New lesions can develop through autoinoculation. Secondary bacterial infection of the lesions may also occur. Spontaneous resolution can occur without scarring.

 Laboratory diagnosis:

          Specimens collected include biopsy of the lesion and the white cheesy material extracted from the lesions. When stained with H&E, either specimen will reveal presence of characteristic intracytoplasmic molluscum inclusion bodies. The inclusion bodies can measure 35 μm in diameter and tend to displace the nucleus to the periphery of the cell.