Smallpox is caused by a virus with the scientific name of variola major. The virus affects only humans, not animals. Like the common cold, it spreads through sneeze and cough emissions, bedding and clothing, or direct contact. After it enters the nose or mouth, it heads for the lymph glands, whence it is given a free ride throughout the body. What happens then is catastrophic: fever, nausea, vomiting—then a rash of hundreds or thousands of blisters, frequently starting on the forehead before covering the entire body. Sometimes the blisters merge together into sheets, rotting off all the underlying skin when they harden. What the virus does inside the body is just as bad—some victims die of thirst when it becomes impossible for them to swallow. The eighteenth-century British noble Lord Dalkeith succumbed after just two days; his limbs fell off while his body was being placed in its coffin.
Like the common cold, smallpox is no respecter of class. It cut down nobles and even monarchs—five in the eighteenth century alone. Smallpox is by far the worst infectious disease humankind has ever known: hundreds of millions have died from it, more than from the Black Death and all the wars of the twentieth century combined. Surviving smallpox is no picnic either; it causes blindness, loss of limbs, and horrible deformity, especially of the face.