Bubonic plague: The most common form of the plague, named for the characteristic buboes -- buboes are enlarged lymph nodes ("swollen glands") -- in the groin which are usually very tender and painful. Lymph nodes may be similarly affected elsewhere such as in the armpits and neck. Common but less specific features of the disease include headache, fever, chills, and weakness.

The bubonic plague is caused by bacteria called Yersinia pestis. The bacteria are transmitted from infected rats to the oriental rat flea to people. (The rats are a "reservoir" for the disease. The fleas are the "vectors" that carry the bacteria from the rat reservoir to the human host.)

The bubonic plague caused the "black death" (the black plague) characterized by gangrene of the fingers, toes, and nose.

See the Plague.