|Description:||This historic image depicted a prairie dog, Cynomys sp., necropsy being performed at the former Public Health Service's Communicable Disease Center plague laboratory in San Francisco, California. This animal was a member of the Chubbs Park, Chaffee County, Colorado prairie dog colony during a 1959 complete colonial die off due to an epizootic plague infection.|
Plague, caused by a bacterium called Yersinia pestis, is transmitted from rodent to rodent by infected fleas.
Plague is characterized by periodic disease outbreaks in rodent populations, some of which have a high death rate. During these outbreaks, hungry infected fleas that have lost their normal hosts seek other sources of blood, thus increasing the increased risk to humans and other animals frequenting the area.
Rock squirrels and their fleas are the most frequent sources of human infection in the southwestern states. For the Pacific states, the California ground squirrel and its fleas are the most common source. Many other rodent species, for instance, prairie dogs, wood rats, chipmunks, and other ground squirrels and their fleas, suffer plague outbreaks and some of these occasionally serve as sources of human infection. Deer mice and voles are thought to maintain the disease in animal populations but are less important as sources of human infection. Other less frequent sources of infection include wild rabbits, and wild carnivores that pick up their infections from wild rodent outbreaks. Domestic cats (and sometimes dogs) are readily infected by fleas or from eating infected wild rodents. Cats may serve as a source of infection to persons exposed to them. Pets may also bring plague-infected fleas into the home.