Smallpox: What the Dermatologist Should Know

Phyllis I. Spuls, MD; Jan D. Bos, MD, PhD; Donald Rudikoff, MD


Skinmed. 2004;3(4) 

In This Article

Clinical Presentation

Smallpox has been classified as variola major, with a mortality rate of 10%-30%, and variola minor, a milder form with a 1% mortality rate.[6] Alastrim virus, which previously caused variola minor in South America, displays minor differences in protein content and DNA structure from variola major,[8,22] which might explain the differing mortality rates. The agent that caused variola minor in Africa is indistinguishable from the variola major form of the virus and the milder clinical illness is not adequately explained.[23] Variola major causes severe disease with prostration, higher fever, and extensive pustulation.[24]

Infection with smallpox requires close, prolonged personal contact; trivial contact usually does not result in spread of the disease. Spread by fomites, like infected clothing and bed linens, is thought to be of minor importance. Variola is less infectious than measles, chickenpox, or influenza. It usually spreads within tight-knit groups like families and less commonly in schools or the workplace. Hospital spread was important in past epidemics.

Historically, smallpox infection resulted from inhalation of respiratory tract secretions from persons with the disease. Oropharyngeal and respiratory mucosal infection spread to the lungs and regional lymph nodes.[6] Asymptomatic viremia then occurred followed by infection of the liver, spleen, bone marrow, and other lymph nodes where the virus multiplied rapidly.

Clinical symptoms began acutely coincident with a secondary viremia, with malaise, high fever, rigors, headache, backache, and fatigue. Abdominal pain, vomiting, and delirium were common. An erosive oropharyngeal enanthem preceded the pustular rash, and during this phase, according to early authors, 10% of light-skinned individuals developed a nonspecific erythematous macular eruption. This enanthem stage represented the period of highest infectivity.[25]

After 2-3 days of high fever, the elevated temperature fell and the classic smallpox eruptions appeared on the face, palms, forearms, and soles and spread rapidly during the next 1-2 days. It started as erythematous macules that quickly and synchronously evolved into papules, vesicles, and then to firm, pearl-like pustules (Figures 1-3). The eruptions then spread centrally to the trunk, but pustules were most abundant on the face and extremities (Figure 4). The disease was most deadly during this stage. Adherent crusts formed 8-14 days after the onset of the rash, and patients remained contagious until the scabs were shed. The crusts left depressed, depigmented scars (pockmarks) on healing in 65%-80% of survivors. These resulted from destruction of sebaceous glands, shrinkage of granulation tissue, and eventual fibrosis.[26] The pustular form of smallpox has been subclassified into discrete, semiconfluent, and confluent forms, and in addition, rapidly fatal hemorrhagic forms have been described.

Smallpox-day 1. Very early on, the exanthem is a nonspecific papular eruption. The severe, febrile prodrome may suggest the diagnosis at this stage. Reprinted with permission from Smallpox and Its Eradication.[6]

Smallpox progression in an unvaccinated boy. Upper left: day 4 of eruption; upper right: day 8 of eruption; lower left: crusting-day 11; lower right: scarring after recovery. Reprinted from Diseases of the Skin and the Eruptive Fevers.[46]

Umbilicated smallpox pustules on the arms. Reprinted with permission from Smallpox and Its Eradication.[6]

Centri fugal smallpox distribution. The eruption starts on the face and forearms, spreads to the lower extremities, and then affects the trunk. Reprinted with permission from Smallpox and Its Eradication.[6]

Facial pockmarks, conjunctivitis, keratitis, corneal ulcers, iritis, and blindness were common sequelae in survivors. Bronchitis and pneumonia also occurred. The mortality rate in unvaccinated and vaccinated individuals with variola major was about 30% and 1%-3%, respectively. Death usually occurred during the second week of illness from toxemia, encephalitis, or hypotension.

In the extremely early stages, the exanthem was not very specific and could resemble measles, secondary syphilis, a drug eruption, pityriasis lichenoides et varioliformis acuta, or varicella. Quick evolution of lesions to the characteristic pustular "pearls" on the face and forearms in a toxic patient removed any doubt as to the diagnosis. Varicella, especially severe forms in immunocompromised patients, would be the condition most likely to be confused with variola. Disseminated herpes simplex infection and extensive secondarily infected molluscum contagiosum lesions could resemble smallpox but are easily excluded by Tzanck smear and direct fluorescent antibody testing. Varicella does not form deep-seated "pearls of pus." Lesions are more superficial, typically appear in crops, are in different stages of development, and are more prominent on the trunk. Symptoms of severe toxicity such as rigors, backache, abdominal pain, and vomiting are much more characteristic of smallpox. The widespread pustular eruption in a critically ill patient or the severe prodrome in an epidemic setting should be unmistakable.[8] The hemorrhagic form of smallpox might be confused with purpura fulminans, meningococcemia, or Stevens-Johnson syndrome.


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