Carried by the fleas on rats, the plague initially spread to humans near the Black Sea and then outwards to the rest of Europe as a result of people fleeing from one area to another.

And we examined reliance on horses, because some scholars suggest — though it’s not yet biologically tested — that the animals carry natural immunity to plague. Regular contact with horses could reduce a population’s susceptibility to the disease.

Dogs and cats may also bring plague-infected fleas into the home. Flea bite exposure may result in primary bubonic plague or septicemic plague. Contact with contaminated fluid or tissue. Humans can become infected when handling tissue or body fluids of a plague-infected animal.

Rats have long been blamed for spreading the Black Death around Europe in the 14th century. Specifically, historians have speculated that the fleas on rats are responsible for the estimated 25 million plague deaths between 1347 and 1351.

20 million people

Great Plague of London, epidemic of plague that ravaged London, England, from 1665 to 1666. City records indicate that some 68,596 people died during the epidemic, though the actual number of deaths is suspected to have exceeded 100,000 out of a total population estimated at 460,000.

[19] Luther said in his 1 John lectures during the plague, “For just as Christ laid down His life and the apostles laid down their lives, so we, too, should lay down our lives, namely, for the strengthening of the faith of the brethren. There are also other occasions, as, for example, when there is a pestilence.

Plague repeatedly struck the cities of North Africa. Algiers lost 30,000–50,000 to it in 1620–21, and again in 1654–57, 1665, 1691, and 1740–42. Plague remained a major event in Ottoman society until the second quarter of the 19th century.