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Orthopoxvirus
is a
genus of viruses to which
belongs variola, the virus
that causes smallpox.
Other members of the
orthopox genus of viruses
capable of infecting
humans include cowpox,
monkeypox and camelpox.
Most
poxviruses are host-species
specific, but vaccinia is a
remarkable exception. True
pox viruses are
antigenically rather
similar, so that infection
by one elicits immune
protection against the
others.
One
of the most widely feared
biological terrorism agents,
smallpox is transmitted by
inhalation and has mortality
rates of 30 - 35% in
untreated exposed
victims. The
incubation period between
contraction and the first
obvious symptoms of the
disease is around 12 days.
Smallpox vaccination within
three days of exposure will
prevent or significantly
lessen the severity of
smallpox symptoms in the
vast majority of people.
Vaccination four to seven
days after exposure likely
offers some protection from
disease or may modify the
severity of disease.
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