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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