Smallpox

Smallpox is caused by the variola virus, a large DNA virus that is unique to humans. Upon entering the host, the virus replicates and settles in the blood vessels of the skin and mucous membranes of the oropharynx and nasopharynx. Direct contact and respiratory droplets are the primary means of spread. The incubation period of this virus averages 12 days after exposure. The initial prodrome of smallpox includes fever, myalgias, and fatigue. Within 4 days after these symptoms, a characteristic vesicular rash appears, most prominent on the face and extremities. Within 3 to 4 weeks, scabs develop, separate, and fall off. Infected persons remain contagious until all lesions have healed. The diagnosis of smallpox is based primarily on physical examination; however, laboratory testing is available for unknown or atypical cases. Currently, no cure for smallpox exists. The most effective means of controlling this illness is prevention—by isolation of infected patients and vaccination of susceptible contacts. Antibiotics and supportive care can be used to prevent secondary complications. Little is known about the effects of smallpox on pregnancy. Pregnant women experience a more severe infection, but fetal complications have not been well defined. Vaccination during pregnancy is not recommended unless there is known exposure to the virus. In light of recent terrorist threats, the potential for an epidemic with enormous public health impact secondary to the intentional release of smallpox has spawned efforts by the Centers for Disease Control and Prevention and other agencies in the United States to prepare for such disaster.