Fleas can transmit a number of diseases to man, most important of which is plague. In the 14th Century, this disease, known as the “Black Death”, killed a quarter of the population of Europe (some 25 million people). In 1665, an epidemic in London killed 70,000 persons out of a total population of 460,000.
In 1900, the plague came to North America. From 1900 to 1925, 432 cases were reported in the United States. There have been no epidemics of plague reported in the United States since 1925, but plague is present in the wild rodent populations of the western states, and generally a few cases of plague, in humans, occur each year from this source. In 1980, nine cases of plague were reported (five from New Mexico, two from California and two from Nevada).