Bubonic plague

Bubonic plague is a zoonotic disease, circulating mainly in fleas on small rodents and is one of three types of bacterial infections caused by Yersinia pestis (formerly known as Pasteurella pestis), which belongs to the family Enterobacteriaceae. Without treatment, the bubonic plague kills about two thirds of infected humans within 4 days. The term bubonic plague is derived from the Greek word βουβών, meaning "groin." Swollen lymph nodes (buboes) especially occur in the armpit and groin in persons suffering from bubonic plague. Bubonic plague was often used synonymously for plague, but it does in fact refer specifically to an infection that enters through the skin and travels through the lymphatics, as is often seen in flea-borne infections. Bubonic plague—along with the septicemic plague and the pneumonic plague, which are the two other manifestations of Y. pestis—is commonly believed to be the cause of the Black Death that swept through Europe in the 14th century and killed an estimated 25 million people, or 30–60% of the European population. Because the plague killed so many of the working population, wages rose and some historians have seen this as a turning point in European economic development.

Bubonic plague in The War That Came Early
Unit 731 experimented with a number of infectious diseases to develop biological weapons including the plague. This proved effective and a delivery system was developed involving porcelain bomb casings filled with rodents infected with the plague. These were shipped to Unit 113 for use in Yunnan Province, in China. The forces of Chiang Kai-Shek were still fighting the Japanese Army and received some supplies from the British in India but the outbreak of disease disrupted this.