Emergency Preparedness

Kern Medical Bioterrorism Response Guide Section 2-C-1 – Smallpox

SMALLPOX (VARIOLA) – OVERVIEW

Naturally Occurring Smallpox Smallpox is a viral disease unique to humans. To sustain itself, the virus must pass from person to person in a continuing chain of infection. Smallpox (variola) was eradicated globally in the late 1970's and routine vaccination was discontinued worldwide following a declaration by the World Health Organization (WHO) that the world was free of smallpox in 1980. Bioterrorism Epidemiology The most likely method of introducing variola or smallpox virus is by intentional aerosolization. The release of smallpox virus into the non-immune population could result in multiple primary exposures with a subsequently large number of secondarily exposed persons if the disease is not recognized quickly. The introduction of one or more deliberately infected infectious persons into a population has also been mentioned as a possibility for a bioterrorist event. The virus can survive in the environment for up to 6 hours when subjected to high temperatures (31 – 33 degrees C) with a relative humidity of 80%. Cooler temperatures and a lower humidity will increase the length of time that the virus will remain viable in the environment. Incubation Period The incubation period ranges from 7-17 days (average is 12-14 days). Transmission Smallpox is transmitted when infectious particles contained in ulcerating lesions in the mouth (tongue, pharynx, larynx and upper part of the esophagus) of an infected person become aerosolized (coughing, breathing or speaking) and are deposited onto the nasal, oral or pharyngeal membranes of a susceptible person. Airborne transmission requires direct face-to-face contact (within 7 feet) with an infected individual and can occur when the infected patient is in the earliest stages of rash development. This stage may be difficult to recognize, therefore, hospitalized patients with presumed or confirmed smallpox should be isolated at the time of admission. Although the virus generally does not travel more than 7 feet from the infected person there have been several reports of more widespread dissemination in hospital settings, presumably by shared ventilation systems. Transmission decreases significantly after the 2 nd week as the oral lesions heal and the viral titers in oral secretions decrease. However transmission may still be possible until all the scabs have separated from the skin. Patients who are coughing may transmit the disease more readily because oral secretions contain a high titer of viral particles. Viral particles are also shed from

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