Chapter 22 Skin Infections
PERSPECTIVE 22.1 The Ghost of Smallpox,An Evil Shade
Historically, smallpox epidemics have been devastating to the Americas. In the 1500s smallpox virus introduced into Central and South America caused horrendous loss of life and may have contributed to the downfall of the Inca and Aztec nations. An epidemic that swept the Massachusetts coast in the 1600s killed so many Native Americans that in some communities there were not enough survivors to bury the dead. Even in the latter 1700s, during the Revolutionary War, a smallpox epidemic raged through the American colonies. General George Washington suspected that the virus had been deliberately introduced by the British. So many of his men were ill after his defeat at Quebec in 1777 that he ordered the mass variolation of remaining troops. ■ smallpox, pp. 497,503, ■ variolation, p. 419
Why does the ghost of smallpox concern us now, when the last case, acquired through a laboratory accident, occurred in 1978? The answer is that the smallpox virus still exists, locked in high-security laboratories in the United States and the Russian Federation, and perhaps held in secret locations by countries or individuals that could use it to harm others. A number of factors need to be considered in choosing the smallpox virus as an agent of bioterror.
Factors that might encourage its use:
■ It spreads easily from person to person, mainly through close contact with respiratory secretions, but also by airborne virus from the respiratory tract, skin lesions, and contaminated bedding or other objects.
■ It can be highly lethal, with mortality rates generally above 25%. After the virus establishes infection of the respiratory system, it enters the lymphatics and bloodstream, finally causing lesions of the skin and throughout the body.
■ The virus is relatively stable, probably remaining infective for hours in the air of a building; viable smallpox has been demonstrated in dried crusts from skin lesions after storage for 10 years at room temperature in ordinary envelopes.
■ Large numbers of people are highly susceptible to the virus. Routine vaccination against smallpox was discontinued in the United States several decades ago.
■ The relatively large genome of the smallpox virus probably permits genetic modifications that could enhance its virulence.
Factors that discourage its use:
■ Propagating the smallpox virus is dangerous and requires advanced knowledge and laboratory facilities.
■ A proven highly effective vaccine (vaccinia virus) is available. A protective antibody response occurs rapidly and prevents fatalities for 10 years or more. Smallpox is prevented even when the vaccine is administered up to four days after exposure to the virus.
■ Infected persons do not spread the disease during the long incubation period, generally 12 to 14 days; they only become infectious with the onset of fever.
■ The disease can usually be diagnosed rapidly, by the characteristic appearance of skin lesions that predominate on the face and hands, and by laboratory examination of material from skin lesions.
■ There is already widespread experience on how to watch for and contain the disease.
In a simulated attack on an American city in the summer of 2001, only 24 primary cases of smallpox grew in 2 months to 3 million, with 1 million deaths.This study probably greatly exaggerated the risk. Nevertheless, even though unlikely, the potential danger from a smallpox introduction has caused the United States to begin preparations for this possibility, including markedly expanding its stockpile of smallpox vaccine.
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