I.

Introduction

Smallpox, highly contagious viral disease that is often fatal. The disease is chiefly characterized by a skin rash that develops on the face, chest, back, and limbs. Over the course of a week the rash develops into pustular (pus-filled) pimples resembling boils. In extreme cases the pustular pimples run together—usually an indication of a fatal infection. Death may result from a secondary bacterial infection of the pustules, from cell damage caused by the viral infection, or from heart attack or shock. In the latter stages of nonfatal cases, smallpox pustules become crusted, often leaving the survivor with permanent, pitted scars.

Smallpox is caused by a virus. An infected person spreads virus particles into the air in the form of tiny droplets emitted from the mouth by speaking, coughing, or simply breathing. The virus can then infect anyone who inhales the droplets. By this means, smallpox can spread extremely rapidly from person to person.

Smallpox has afflicted humanity for thousands of years, causing epidemics from ancient times through the 20th century. No one is certain where the smallpox virus came from, but scientists speculate that several thousand years ago the virus made a trans-species jump into humans from an animal—likely a rodent species such as a mouse. The disease probably did not become established among humans until the beginnings of agriculture gave rise to the first large settlements in the Nile valley (northeastern Africa) and Mesopotamia (now eastern Syria, southeastern Turkey, and Iraq) more than 10,000 years ago.

Over the next several centuries smallpox established itself as a widespread disease in Europe, Asia, and across Africa. During the 16th and 17th centuries, a time when Europeans made journeys of exploration and conquest to the Americas and other continents, smallpox went with them. By 1518 the disease reached the Americas aboard a Spanish ship that landed at the island of Hispaniola (now the Dominican Republic and Haiti) in the West Indies. Before long smallpox had killed half of the Taíno people, the native population of the island. The disease followed the Spanish conquistadors into Mexico and Central America in 1520. With fewer than 500 men, the Spanish explorer Hernán Cortés was able to conquer the great Aztec Empire under the emperor Montezuma in what is now Mexico. One of Cortés's men was infected with smallpox, triggering an epidemic that ultimately killed an estimated 3 million Aztecs, one-third of the population. A similar path of devastation was left among the people of the Inca Empire of South America. Smallpox killed the Inca emperor Huayna Capac in 1525, along with an estimated 100,000 Incas in the capital city of Cuzco. The Incas and Aztecs are only two of many examples of smallpox cutting a swath through a native population in the Americas, easing the way for Europeans to conquer and colonize new territory. It can truly be said that smallpox changed history.

Yet the story of smallpox is also the story of great biomedical advancement and of ultimate victory. As the result of a worldwide effort of vaccination and containment, the last naturally occurring infection of smallpox occurred in 1977. Stockpiles of the virus now exist only in secured laboratories. Some experts, however, are concerned about the potential use of smallpox as a weapon of bioterrorism. Thus, despite being deliberately and successfully eradicated, smallpox may still pose a threat to humanity.