Smallpox was a disease that was caused by a virus. The virus spread when an uninfected person came in direct contact with a sick person and breathed in the virus. Usually, the virus was in tiny drops that were coughed up by the sick person. After about two weeks the infected person would develop a high fever and muscle aches and pains. After about three days of fever the person would break out in a rash all over his or her body. At first it looked like red spots, but these spots gradually became blisters that were about the size of a pencil eraser. After about five days of rash, the fluid in the clear blisters turned to pus. The more pus spots that a person had, the more likely he or she was to die.
There were two main types of a smallpox virus. Variola major, which killed about 20 percent of the people who were infected and variola minor, which killed about 2 percent of its victims. If a person did not die, the pus gradually dried up to form scabs that dropped off after one or two weeks. The pus spots on the face often left permanent scars known as pockmarks.
Smallpox was known to the ancient peoples of China, India, and Egypt. Pharaoh Ramses V died of it in 1157 BC. It spread wherever large numbers of people moved, and it was a very serious problem in cities where people lived close together. It first reached Europe in the fifth century, and it was one of the leading causes of death in the 16th and 17th centuries. It was brought to the Americas many times during that period, first by the Spanish conquerors and later by African slaves, where it wiped out many native American populations.
The Hindu god Krishna is believed to have loved milkmaids because of their beautiful, unscarred, complexions. Milkmaids, of course, spent a lot of time around cows, which are carriers of cowpox, a virus similar to the smallpox virus. In 1796 the British physician, Edward Jenner, after noting that milkmaids were spared the smallpox, demonstrated that if he...