Smallpox.

According to the Washington Post, Cabinet officials gathered at the White House on Saturday for a drill simulating a smallpox attack against the United States. Its kind of like when Ms. Demarco gets bored and throws us outside in below zero weather for random fire drills; it gets everybody in a panic and passes the time. The exercise lasted four hours and was initiated to test the government's response plans. Although the disease was last eliminated in the 80's, there are fears that smallpox could be used by terrorists as a biological weapon. President Bush did not participate in the exercise. This excercise showed that saving lives and containing economic damage would require more planning in local communities and increased production of vaccines and medications.
The first smallpox epidemic probably reached America around 1519. In 1519, Hernan Cortes landed on the shores of what is now Mexico and was then the Aztec empire. n 1520, another group of Spanish came from Cuba and landed in Mexico. Among them was an African slave who had smallpox. When Cortés heard about the other group, he went and defeated them. In this contact, one of Cortés's men contracted the disease. When Cortés returned to Tenochtitlan, he brought the disease with him. Soon, the Aztecs rose up in rebellion against Cortés. Outnumbered, the Spanish were forced to flee. In the fighting, the Spanish soldier carrying smallpox died. After the battle, the Aztecs evidently looked on the invaders' bodies for riches and contracted the virus. Smallpox then devastated the Aztec population. It killed most of the Aztec army, the emperor, and 25% of the overall population.