Plague and other yersinia infections

[Lanell]

Plague is a severe infection caused by the gram-negative bacteria Yersinia pestis and often involving the lymph nodes and/or lungs.

The bacteria are spread mainly by the rat flea.
Depending on the form, plague can cause fever, chills, swollen lymph nodes, headache, a rapid heartbeat, cough, difficulty breathing, vomiting, and diarrhea.
Identifying the bacteria in samples of blood, sputum, or pus from lymph nodes confirms the diagnosis.
Antibiotics can reduce the risk of death, and isolating infected people helps prevent spread of plague.

(See also Overview of Bacteria.)
In the past, massive plague epidemics, such as the black death of the Middle Ages, killed many people. The main contributing factors were large numbers of rodents, urban crowding, and poor sanitation.
Plague now occurs sporadically or in limited outbreaks.
In the United States, more than 90% of infections occur in rural or semirural areas of southwestern states such as Arizona, California, Colorado, and New Mexico, particularly among campers. In recent decades, plague affects an average of about 7 people a year (ranging from 1 to 17 people) in the United States.
Worldwide, most cases since the 1990s have occurred in Africa, with recent outbreaks in Madagascar.