Bubonic plague usually starts one to five days after infection with a fever, shivering, and a severe headache.
Sometimes, septicemia (blood poisoning) is an early complication and it may cause death before other signs of the disease appear.
The plague may have three clinical forms: bubonic, pneumonic (pneumonia), or septicemic (blood poisoning). The misleading use of the word bubonic (which means that it is characterized by buboes, or inflammatory swellings of lymph nodes) has developed into the mistaken idea that the real plague is necessarily bubonic and that non-bubonic types are a different disease altogether.
The mild forms of plague infections are bubonic while the other forms are severe and almost always fatal, unless properly treated; and the bubonic plague consists of about three-fourths of the total kinds of plague cases.