Pediatric emergency medicine trisk 4551 4551
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cessation of universal vaccination within the United States in 1972, vaccine had
been out of production until the 2007 licensing of a new product (ACAM2000,
Acambis Corporation); although the CDC now controls enough ACAM2000 to
vaccinate every American, susceptibility to the disease is nearly universal. Also,
effective therapy is lacking and healthcare providers are unfamiliar with the
disease. Finally, the potential for rapid spread potentially permits a terrorist to
cause widespread disease and panic with a minimum of infectious material.
Pathophysiology. Although infectivity is highest when the smallpox rash first
appears, the disease may be spread by exposed persons about 24 hours before the
exanthem manifests. During the 7- to 17-day long incubation period, the virus
replicates in upper respiratory tract mucosa, giving rise to a primary viremia. The
liver and spleen are then seeded, further amplification of the virus occurs, and a
secondary viremia ultimately develops. The skin is seeded with this secondary
viremia, and the classic exanthem of smallpox develops.
Clinical Manifestations. Clinical illness has an abrupt onset during the phase of
secondary viremia and is characterized by fever, malaise, rigors, vomiting,
headache, and backache. The classic exanthem typically begins 2 to 4 days later
as macules on the face and extremities. These lesions progress in synchronous
fashion to papules, vesicles, and then to pustules, which finally form scabs. As
scabs separate, survivors are left with disfiguring depigmented scars. The rash
spreads centrally to the trunk but remains more abundant at the periphery. This
centrifugal distribution and synchrony distinguish smallpox from chickenpox,
which has a centripetal distribution of lesions in varying stages of development.
An enanthem usually accompanies the characteristic exanthem, and internal
organs become viral targets as well. Death historically occurred in approximately
30% of variola major (the predominant form of smallpox in the past) patients and
typically resulted from hypotension and immune complex–associated toxemia.
Eye involvement led to blindness in a small number of victims. Uncommon
variants with lesser (variola minor) or greater (hemorrhagic and flat-type variants)
mortality also existed. Ominously, a 1971 smallpox outbreak in Aralsk, in the
former Kazakh Soviet Republic, is thought by some to have originated from a
bioweapons accident. All three fatalities in this small outbreak involved
unvaccinated individuals who contracted rare and universally fatal hemorrhagic
disease, raising the specter of genomic manipulation for increased virulence.
Management. The diagnosis of smallpox should be suspected on clinical
grounds. Laboratory confirmation (e.g., electron microscopy, PCR) is best
