SMALLPOX :CLINICAL ASPECTS
The incubation period of smallpox is usually 12 to 14 days, although in occasional fulmi-nating cases it can be as short as 4 to 5 days. The typical onset is abrupt, with fever, chills, and myalgia, followed by a rash 3 to 4 days later. The rash evolves to firm papulovesicles that become pustular over 10 to 12 days, then crust and slowly heal. Only a single crop of lesions (all in the same stage of evolution) develop; these lesions are most prominent over the head and extremities (Fig 35–2). Some cases are fulminant, with a hemorrhagic rash (“sledgehammer” smallpox). Death can result from the overwhelming primary viral infec-tion or from bacterial superinfection. Diagnostic methods utilize vesicular scrapings, and include culture, electron microscopy, gel diffusion, and polymerase chain reaction.
The first major step toward modern prevention and subsequent eradication of smallpox can be credited to Edward Jenner, who noted that milkmaids who develop mild cowpox lesions on their hands appeared immune to smallpox. In 1798, he published evidence in- dicating that purposeful inoculation of individuals with cowpox material could protect against subsequent infection by smallpox. The concept of vaccination gradually evolved, with the modern use of live vaccinia virus, a poxvirus of uncertain origin to be discussed later, which produced specific immunity.
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