An acute infectious viral disease characterized by severe systemic involvement and a single crop of skin lesions that proceeds through macular, papular, vesicular, and pustular stages. Smallpox is caused by variola virus, a brick-shaped, deoxyribonucleic acid–containing member of the Poxviridae family. Strains of variola virus are indistinguishable antigenically, but have differed in the clinical severity of the disease caused. From at least 1157 B.C., when the disease probably killed the Egyptian Pharaoh Ramses V, hundreds of millions of cases and millions of deaths due to smallpox occurred throughout the world. On October 26, 1977, Ali Maow Maalin, a cook from Merca, Somalia, had onset of the smallpox rash; he was the last patient to contract the disease through natural transmission, although a laboratory outbreak of smallpox occurred in the United Kingdom in 1978. Following a 13-year worldwide campaign coordinated by the World Health Organization (WHO), smallpox was declared eradicated by the World Health Assembly in May 1980. Smallpox is the first human disease to be eradicated.