The bubonic plague is an infection of the lymphatic system, usually resulting from the bite of an infected flea. The fleas are often found on rodents, such as rats, and seek out other prey when their rodent hosts die. Once established, bacteria rapidly spread to the lymph nodes and multiply. Yersinia pestis can resist phagocytosis and even reproduce inside phagocytes and kill them. As the disease progresses, the lymph nodes can hemorrhage and become necrotic. Bubonic plague can progress to lethal septicemic plague in some cases. The plague is also known to spread to the lungs and become the disease known as the pneumonic plague.
