Smallpox

Transmission

Usually by respiratory droplet transmission, following close face-to-face contact. Smallpox was also transmitted by direct contact with skin lesions or drainage, or with contaminated objects. Although uncommon, airborne transmission (longdistance) also occurred.
  • Variola virus is predominantly transmitted person-to-person via inhalation of droplet nuclei (Fenner 1988). Transmission occurs most commonly among those with close face-to-face contact with an infected patient (particularly household contacts, since patients are usually ill enough to be confined to bed during the period of infectiousness).
  • Airborne transmission has been documented in two outbreaks that occurred in hospitals in the Federal Republic of Germany (one in 1961 and one in 1970) (Wehrle 1970).
    • In the first outbreak, the index patient transmitted the virus to 19 persons, 10 of whom had no direct contact with the patient. The index patient had severe confluent skin involvement, ulcerative pharyngitis, and a barking cough.
    • In the second outbreak, the index patient transmitted the virus to 17 persons, none of whom had direct contact with the patient. The index patient had severe confluent skin lesions, severe bronchitis, and cough. Investigators noted that the relative humidity in the hospital was low (which may have facilitated survival of the virus) and that the design of the hospital set up strong air currents throughout the building (which may have facilitated dissemination of viral particles).
  • Fomite transmission (eg, from clothing and bedding) has been reported (Dixon 1962: Smallpox. London, England: J & A Churchill Ltd, 1962, Kiang 2003). Contaminated blankets were used for intentional transmission of smallpox during the French and Indian War in the United States in the 1700s (Stearn 1945: The effect of smallpox on the destiny of the Amerindian. Boston, MA: Bruce Humphries, 1945).
  • Transmission via direct contact with skin lesions and infected body fluids also has been recognized (Kiang 2003).
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