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.
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.