Modes of Transmission

General Information on Transmission

Transmission of smallpox is respiratory, through inhalation of airborne variola virus, usually droplets expressed from an infected person.(19:12) An infected person passes the virus to others in close contact, often by coughing. (12:59) Most transmission results from direct face to face contact with an infected person, usually within a distance of 6 feet, or from physical contact with a person with smallpox or contaminated articles.Transmission to laundry workers by infected bedding has been reported during several outbreaks by Dixon and others. The environment immediately around the patient (e.g. pillow, bedclothes) had the highest percentage of positive cultures. This would correspond to areas where respiratory droplets would be most likely to settle and where pustule drainage contamination would be the greatest. (12:59) The virus can remain viable for several days in a controlled environment. In temperate climates, scabs from smallpox patients, in which the virus is contained in a fibrin matrix, can retain viable virus for several years when held at room temperature. (19:4)

A person with variola virus is not infectious during the incubation period, or during the first day or two of the prodromal stage of the illness. The patient becomes infectious with the first appearance of the rash, which is accompanied by lesions in the mouth and pharynx. In general, persons with a severe rash and involvement of the mouth and pharynx are more infectious than those with a slight rash. (19:12)

There is an interval of two to three weeks between each generation of cases. Smallpox generally spreads less widely and less rapidly than varicella or measles. (19:12)

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