During World War 2, Japan bombed China with fleas infected with the bubonic plague.
“This attack was known as the Kaimingjie germ weapon attack, where Japanese troops, including ones from Unit 731, dropped corn, wheat, and cotton infested with fleas carrying the bubonic plague, cholera, typhoid, and other diseases in Chinese cities to start an outbreak. The infested areas were burned down, but it’s estimated that this attack, among others, resulted in about 300,000 deaths.”