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Smallpox is a disease caused by the Variola virus (of the family Proxviridae). There are two variants of the virus: Variola major and Variola minor (with Variola major causing the most dangerous form of smallpox, and Variola minor causing variants that have a lower risk of being fatal, such as the diseases asalastrim, cottonpox, milkpox, whitepox, and Cuban itch). The route of transmission is airborne, via droplets expressed from the oral, nasal, or pharyngeal mucosa of an infected person. The disease is clinically significant with a high mortality rate in the unvaccinated host (estimates place the mortality rate at around 30 percent). Furthermore, the disease is regarded as highly contagious. In pregnant women, the virus can theoretically cross the placenta. Following an extension vaccination and ...

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