The bacterium that causes Lyme disease is at least 60,000 years old and existed long before the U.S. bioweapons program. Scientists have observed suspected cases of Lyme disease in several locations well before the first identified case of the disease in the 1970s, including in a 5,000-year-old mummy near the Austria-Italy border.
Lyme disease became endemic in the U.S. in the 1970s because of suburbanization and a warming climate, which increased both ticks carrying the Lyme disease bacterium and the number of animals, such as the white-tailed deer, on which the ticks feed. Humans also began living closer to these animal populations, spurring the disease to spread more rapidly.
Experts also said Lyme disease would make a poor bioweapon because of its low fatality rate and its transmission through ticks.