Most of these occur during the months of May to October when people are outdoors and come into contact with rodents and fleas. Plague is primarily a zoonotic infection. It is transmitted among the natural animal reservoirs which are predominantly urban and sylvatic rodents, by flea bites, and by ingestion of contaminated animal tissues. Throughout the world, the urban and domestic rats, Rattus rattus and R. morvergicus are the most important reservoirs of the plague bacilli. The most efficient vector for transmission is the oriental rat flea, Xenopsylle cheopis .
Humans become accidental hosts in the natural cycle of plague when bitten by infected rodent fleas.
In the United States, males and females have been equally effected. Sixty percent of cases occur in persons less than 20 years old. Status Killing of dogs to prevent the spread of the plague. As a result of the great discovery of Louis Pasteur and Robert Koch, scientists had a better chance of fighting the plague. Pasteur s studies on the involvement of microorganism in causing disease, and Koch s discovery of how to grow bacteria in controlled environments and to isolate the pathogen was a great discovery for modern science.