A fox terrier helped in the prevention of the bubonic plague after San Francisco's massive earthquake in the early 1900s.
The earthquake shook San Francisco on April 18, 1906 a little after 5 a.m. with a magnitude close to 8, killing an estimated 3,000 people and leaving more than 250,000 people homeless. About 80% of the city's infrastructure were ruined, with rats massing over destroyed land and open sewers.
According to John J. Conlon, a boy at the time, "There was a bubonic plague scare shortly after the fire and because the fleas on rats were carriers of the germs, the City paid a bounty for dead rats. These bounty payments were my introduction to the functions of the "middle man." An older lad enriched himself by paying the neighborhood youngsters with candy for dead rats. The rats he exchanged for cash at the repaired Emergency Hospital. The fire drove thousands of rats into our district and mother was horrified by them. Consequently, to avoid attracting them, all were instructed to securely cover garbage cans. Every morning, after the women had deposited the breakfast trash in the cans, I would remove the covers. Returning in about an hour, I would inspect the galvanized cans, and if any rats were trapped therein, cans were tipped so that my fox terrier could kill the emerging rodent; then to the "middle man" for candy."
Despite the preventive measures, outbreaks did occur. San Francisco was finally declared plague-free in 1908.