Smallpox

Epidemiology

• Highly infectious after aerosolization
• Person-to-person transmission can occur via droplet nuclei or aerosols expelled from the oropharynx and by direct contact
• Contaminated clothing or bed linens can also spread the virus
• About 30% of susceptible contacts will become infected

Clinical

• Incubation period is 12-14 days (ranges 7-17 days)
• Characteristic rash appears 2-3 days after nonspecific, flu-like prodrome (fever and headache)
• Maculopapular rash begins on mucosa of mouth and pharynx, face, hands, forearms and spreads to legs and centrally to trunk; lesions are more predominant on the face and extremities than on the trunk.
• Lesions progress synchronously on any given part of the body from macules to papules to vesicles to pustules to crusty scabs

Laboratory Diagnosis

• Mask and gloves should be worn by person obtaining specimen, preferably a person who has been recently vaccinated
• Vesicular fluid is obtained by opening lesions with the blunt edge of a scalpel, harvesting fluid with a cotton swab; scabs can be removed by forceps. Swabs and scabs should be placed in a vacutainer, sealed with tape, and placed in a second, durable, watertight container
• Laboratory specimens must be handled in a Biosafety Level 4 facility (e.g. CDC) and will be evaluated with electron microscopy and cell culture

Patient Isolation

• Strict isolation in negative pressure room (high efficiency particulate air filtration ideal) from onset of rash until all scabs separate
• Laundry and waste should be autoclaved before being laundered or incinerated

Treatment

• Supportive care is the mainstay of therapy
• In-vitro antiviral activity against poxviruses has been shown with adefovir, cidofovir, dipivoxil, and ribavirin. (Animal studies suggest that cidofovir may be most effective).

Prophylaxis

• Smallpox vaccine would be required for all persons exposed at the time of the bioterrorist attack or anyone with close personal contact with a smallpox case
• Vaccine is most effective if given before of within 3 days of exposure
• Ideally, all exposed persons should be placed in strict quarantine for 17 days after last contact with a smallpox case