Naturally Occurring Infection
Humans are the only natural reservoirs of variola virus.
Person-to-person transmission of smallpox occurs by aerosol
droplets expelled from the oropharynx of infected persons,
or by direct contact with an infected person. The virus can
also be spread through contaminated bedding and clothing.
Despite the fact that smallpox is less contagious than influenza
or measles, it is still considered a highly contagious disease.
The infectious dose 50, the amount of agent inhaled in aerosol
form that is required to cause manifest illness in 50% of
susceptible humans, is less than 100 viral particles. The
patient can be already infectious in the last day of
incubation period, and remains contagious until the scabs
separate. The virus can remain viable for months on objects
from the victim's surroundings. Though smallpox is spread most
readily during dry, cool winter months, the disease can be
transmitted in any climate and in all parts of the world.
Physical protection, early vaccination, and isolation of
infected patients are the only effective protection against
the disease. Patients vaccinated within 2 or 3 days of exposure,
will most likely not develop the disease. Vaccination 4 or 5 days
after exposure may significantly reduce mortality, but will less
effectively reduce morbidity.
Contents: Smallpox (Extensive Information)
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