Smallpox & Vaccinia

Essentials of Diagnosis

• Prodromal high fever

• Eruption progressing from papules to vesicles to pustules, then crusts

• All lesions in the same stage

• Face and distal extremities (including palms and soles) favored

General Considerations

• Recent reintroduction of vaccination for first-responder and military population because of bioterrorist threat

• The incubation period for smallpox averages 12 days (7–17 days)

• Immunization with vaccinia is not recommended for persons with eczema, in whom widespread vaccinia (eczema vaccinatum) may result, with lesions resembling those of smallpox

• Exposure to a recently vaccinated person may lead to generalized disease in persons with certain skin diseases

• Prior vaccination does not prevent generalized vaccinia, but previously vaccinated individuals have milder disease

• Progression of the primary inoculation site to a large ulceration occurs in persons with systemic immune deficiency, with a possible fatal outcome

Symptoms and Signs

Smallpox

• Prodrome

  • Abrupt onset of high fever

  • Severe headaches, and backaches

  • Infected person appears quite ill

• Infectious phase

  • Appearance of an enanthem, followed in 1–2 days by a skin eruption

  • Lesions begin as macules, progressing to papules, then pustules, and finally crusts over 14–18 days

  • The face is affected first, followed by the upper extremities, the lower extremities, and trunk, completely evolving over 1 week

  • Lesions are relatively monomorphous, especially in each anatomic region

• All lesions in same stage of development differentiates rash from varicella

Vaccinia

• Inoculation with vaccinia produces a papular lesion on day 2–3 that progresses to an umbilicated papule by day 4 and a pustular lesion by the end of the first week

• The lesion collapses centrally, and crusts, with the crust eventually detaching up to a month after the inoculation

Differential Diagnosis

• Generalized varicella zoster virus (VZV) infection

• Generalized herpes simplex virus (HSV)

Laboratory Tests

• Direct fluorescent antibody testing for HSV and VZV are first-line diagnostic tests to differentiate VZV, HSV, vaccinia, and smallpox

• Smallpox is a clinical diagnosis but viral infection can be confirmed by electron microscopy, antigen detection, and polymerase chain reaction

Medications

• No specific and proven antiviral therapy for vaccinia or smallpox

• Vaccinia immune globulin is used to treat eczema vaccinatum and progressive vaccinia

• Cidofovir may have some activity against these poxviruses

Therapeutic Procedures

• Strict respiratory and contact isolation crucial

• Patient should be immunized if in early stage of disease

• No antiviral therapy clearly effective

• Supportive care critical

• Centers for Disease Control and Prevention should be contacted immediately in the event of suspected case(s)

Complications

• Serious complications in about 5/100,000 persons include encephalitis, progressive vaccinia, and eczema vaccinatum

Prognosis

• Generalized vaccinia may be fatal

Prevention

• U.S. vaccination campaign voluntary, focusing on first responders and military personnel

When to Admit

• Until the diagnosis is confirmed, strict isolation of the patient is indicated