The things I saw beggar description. The visual evidence and the verbal testimony of starvation, cruelty and bestiality were so overpowering as to leave me a bit sick."
Gen. Dwight D. Eisenhower to Gen. George C. Marshall
April 15, 1945
describing visit to a German concentration camp
The Black Death, often called the plague, is caused by the bacterium Yersinia pestis, not a virus. This Gram-negative rod-shaped bacterium infects humans primarily through bites from infected fleas, such as Xenopsylla cheopis, which thrive on rodents like black rats.
Key Characteristics
Yersinia pestis is a facultative anaerobe that survives in flea digestive tracts by forming biofilms, blocking the flea’s gut and prompting regurgitation of infected blood into new hosts. It evades the immune system via proteins like Yop effectors injected through a type III secretion system, leading to rapid bacterial multiplication in lymph nodes. The bacterium spreads via bubonic (lymphatic), septicemic (bloodstream), or pneumonic (lungs) forms, with pneumonic being highly contagious through respiratory droplets.
