Plague

**Semantic type:** Disease or Syndrome

**Definition:** A Gram-negative bacterial infection caused by Yersinia pestis. It is usually transmitted to humans from bites of infected rodent fleas. It is manifested as a bubonic, septicemic, or pneumonic plague. In bubonic plague, the lymph nodes adjacent to the site of the skin bite are infected and enlarged. In septicemic plague, the infection spreads directly through the bloodstream. In pneumonic plague, the infection spreads to the lungs either following bubonic plague, or by inhalation of infective droplets. If untreated, it may lead to death.