Smallpox

Smallpox was a virus that covered the sufferer with unpleasant, pus-filled sores. The virus deceived the immune system into attacking the body’s own organs, eventually leading to an agonizing death.

Historians believe that, in 1525, a single diseased Spaniard infected Incan society with smallpox. Within a year, almost nothing remained of the 7,000-year-old civilization that had ruled over an area as large as Italy and Spain combined.

In fact, Incan civilization was so devastated by the disease that, just seven years after the arrival of smallpox, the Spanish conquistador Francisco Pizarro was able to conquer the Incan empire with only 168 men.

Theoretically at least, the Incas had an army of 80,000 at their disposal – but smallpox had incapacitated them en masse.

Most Spaniards had some immunity to the disease, as it had already been present in Europe for many years. However, the indigenous American peoples had no such immunity, and the virus would eventually go on to kill 90 percent of them.

Although it arrived too late to save the indigenous Americans, a smallpox vaccine was eventually developed in the eighteenth century.

The vaccine’s development began with an observation made by Edward Jenner, an English physician. He noticed that milkmaids tended not to contract smallpox, and realized that they had effectively inoculated themselves against the more severe smallpox virus by catching the less severe cowpox from the milk herd.

It was from this discovery that Jenner was able to design the world’s first smallpox vaccine using the cowpox virus. Vaccination proves a massive success; by the end of the twentieth century, smallpox had been eradicated.