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Viral infections of skin and mucosa produce a wide spectrum of local and systemic manifestations.

  • Human papillomavirus (HPV) and molluscum contagiosum virus (MCV) colonize the epidermis of most individuals without causing any clinical lesions. Benign epithelial proliferations such as warts and molluscum occur in some colonized persons, are transient, and eventually resolve without therapy. In immunocompromised individuals, however, these lesions may become extensive, persistent, and refractory to therapy.

  • Primary infections with many viruses cause acute systemic febrile illnesses and exanthems, are usually self-limited, and convey lifetime immunity. Smallpox caused severe morbidity and mortality, but no longer occurs because of worldwide immunization.

  • Eight human herpesviruses (HHV) often have asymptomatic primary infection but lifelong latent infection. With host defense defects, herpes viruses can become active and cause disease with significant morbidity and mortality.


  • Poxvirus family is a diverse group of epitheliotropic viruses that infect humans and animals. Only smallpox virus and molluscum contagiosum virus (MCV) cause natural disease in humans. Smallpox virus causes systemic infection with exanthema, i.e., smallpox or variola. MCV causes localized skin lesions. Human orf and milker's nodules are zoonoses that can occur in humans, given exposure to infected sheep or cattle. Other poxviruses zoonoses occurring in monkeys, cows, buffalo, sheep, and goats can also infect humans.


  • Molluscum contagiosum is a self-limited epidermal viral infection.

  • Clinical Manifestation. Firm pearly papules; often umbilicated. Few to myriads of lesions. Host defense defects: large nodules with confluence.

  • Course. In healthy persons, resolves spontaneously.


ETIOLOGY MCV with four discrete viral subtypes, I, II, III, IV; type I is responsible for >90% cases. Not distinguishable from other poxviruses by electron microscopy. MCV colonizes the epidermis and infundibulum of hair follicle. Transmitted by skin-to-skin contact.

DEMOGRAPHY More common in children and sexually active adults. In advanced human immunodeficiency virus (HIV) disease, hundreds of small mollusca or giant mollusca occur on the face and other sites.

PATHOGENESIS A subclinical carrier state of MCV probably exists in many healthy adults. Unique among poxviruses, MCV infection results in epidermal tumor formation; other human poxviruses cause a necrotic "pox" lesion. Rupture and discharge of infected cells occur in the umbilication/crater of the lesion.


Papules, nodules, and tumors with central umbilication or depression (Figs. 27-1, 27-2, 27-3, 27-4). Skin-colored. Round, oval, hemispherical. Isolated single lesion; multiple, scattered discrete lesions; or confluent mosaic plaques. Larger mollusca may have a central keratotic plug, which gives the lesion a central dimple or umbilication. Gentle pressure on a molluscum extrudes the central plug.

Figure 27-1

Molluscum contagiosum Typical umbilicated papules. Discrete, solid, skin-colored papules 3 to 5 mm on the chest of an adolescent ...

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