Characteristics.
The smallpox virus is an orthopox virus
with a narrow host range confined to
humans. Eradication of the natural
disease was completed in 1977. Appearance
of human cases would signal use of the
virus as a biological weapon. Under
natural conditions, the virus is
transmitted by direct contact with an
infected case, by fomites, an
occasionally by aerosols. Smallpox virus
is highly stable and retains infectivity
for long period outside of the host. A
related virus, monkeypox, clinically
resembles smallpox and causes sporadic
human disease in West and Central Africa.
The incubation period is typically 12
days (range, 10-17 days).
Clinical
Features. The illness begins
with a prodrome lasting 2-3 days, with
generalized malaise, fever, rigors,
headache, and backache.
This is followed
by defervescence and the appearance of a
typical skin eruption characterized by a
7-10 day progression of lesions, through
successive stages, from macules to
papules to vesicles to pustules. The
latter finally form crusts and, upon
healing, leave depressed depigmented
scars. The distribution of lesions is
centrifugal (more numerous on face and
extremities than on the trunk). Lesions
are in the same stage of development at
any point in time. Fever may reappear
around the 7th day after onset of rash.
The case fatality rate is approximately
35% in unvaccinated individuals.
Patient
Management. While smallpox
patients were often cared for by immune
care givers using standard (or no)
precautions, the care of smallpox
patients today would involve cohorting
and quarantine in designated facilities,
vaccination (to protect those possibly
misdiagnosed), and the use of contact
and, if possible, airborne precauations;
respiratory droplet precautions might be
the only feasible alternative in a mass
casualty situation. All contacts
including healthcare workers would be
vaccinated and quarantined. Objects in
contact with the patient (e.g. bed
linens, clothing, ambulances) require
disinfection by fire, steam, or sodium
hypochlorite solution.
Vaccine/Prophylaxis.
Smallpox vaccine (vaccinia virus) is a
licensed live pox virus vaccine that
induces strong cross-protection against
smallpox. Reliable data are sparese as to
efficacy and durability of protection.
The duration vaccinia induced immunity is
at least 3 years. Vaccine immunity may
prevent or modify illness. Fully immune
individuals exposed to the virus by the
respiratory route may develop fever, sore
throat, and conjuctivitis ("contact
fever") lasting several days. The
vaccine is administered by dermal
scarificatio or intradermal jet
injection. The appearance of a vesicle or
pustule within several days indicates
that the vaccine will be effective. Other
available countermeasures include the
post-exposure use of Vaccinia immune
globulin or primary vaccination within
3-4 days of exposure yields some
protection.
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Medical
Management of Biological Agent Patients
