Smallpox is an acute infectious disease caused by the variola virus. Variola virus infection is initiated when the virus comes into contact with the oropharyngeal or respiratory mucosa. The virus localizes in the blood vessels of the dermis and oral and pharyngeal mucosa, resulting in the characteristic maculopapular rash, which evolves into vesicles, then pustules. The overall fatality rate for ordinary-type smallpox is about 30 percent. Other more severe types of smallpox have 90 percent and higher fatality rates.
Smallpox is preventable by vaccination. The last case of smallpox in the United States was reported in 1949. In the early 1950s, an estimated 50 million cases occurred worldwide each year. Intensified worldwide smallpox eradication programs began in 1966; and as a result of these efforts, the last case of indigenous smallpox occurred in 1977. In 1980, the World Health Organization certified the global eradication of smallpox and recommended that all countries cease vaccination.
Recent events have caused political and scientific leaders to consider the possibility that smallpox virus could be utilized as a Category A biological weapon. Therefore, extensive national and state plans have been adopted in the event release of the variola virus occurs.
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