Epidemiology – Natural Reservoirs
- Humans acquire plague most often through the bites of infected
rodent fleas. For naturally occurring cases of plague, the Oropsylla
montana flea is the primary vector for plague. This type
of flea is found mostly in rural rodent species, particularly
the Rock Squirrel in New Mexico and Arizona. Urban plague from
rats has not occurred in the U.S. in over 70 years. This is
due to good public health surveillance and control and improved
sanitation measures. If an urban plague event (natural or bioterrorism
related) was to occur, the Xenopsylla cheopsis flea
or "rat" flea would be the flea of most concern.
- The flea ingests a blood meal from a bacteremic animal. The
bacteria multiply and block the gut of the flea. When the flea
attempts to feed again, it regurgitates bacteria into human
or animal mammalian host.
- The most common reservoirs for the bacteria are ground squirrels
and wood rats.