“,,, and of course killing rodents reduced disease.”
You might think so. But it turns out that the fleas that carry the bubonic plague bacterium Yersinia pestis or “The Black Death” strongly prefer rodent hosts to humans. If you kill off the rodents the fleas hold out for a while and then jump to human hosts. And then it’s off to the races.
Rodents are disease spreaders beyond the bubonic plague .