Yersinia pestis is
a flea born disease. The vector flea finds a victim and tries to
feed by injecting its sucking mechanism, but the bacilli has blocked the
flea's esophagus and pharynx, preventing it from obtaining any blood. This
causes the flea to continuously puncture its food source, in turn
regurgitating into the wound and injecting it with the plague bacilli.
Photo: Centers for Disease Control and Prevention
The bacteria is generally
hosted by rodents such as ground squirrels, kangaroo, urban rats, mice,
prairie dogs, and chipmunks, but it can also be found in soil
contaminated by infected dead fleas and rodents. More than 200
species of rodents are able to carry various degrees of the disease.