I was reading an article today on the plague in early modern Egypt and it struck me how they readily attributed disease to the land (i.e. environment), but it never seems to occur to anyone to suspect insect vectors or even rats. Up through early modern times people readily linked disease with geography, especially bad air (mala – aria, literally bad air) but rarely water and hardly ever other creatures, insects or rodents. In the case of malaria, they did get close in making the link between night air and damp or air off of water and malaria. The real link of course being that mosquitoes are found most often near water and at night.
One of the chief complaints that skeptics of Yersinia pestis as the agent of the medieval plagues make is the absence of rats or fleas in plague texts. This really shouldn’t be a surprise at all considering no one thought that mosquitoes carried disease then either. It just didn’t occur to them that insects could transmit disease. If they didn’t understand the fleas, why comment on the rats? There would be no reason to mention animals that were not economically important. Who would really care that there was a lack of rats? Besides most sick rodents will crawl back into their burrow or similar safe place to die. Sick rats like to feel safe and comfortable toward their end just like humans and other animals. The point being they are out of sight when they die and their bodies are often never found. Dying in a burrow they essentially bury themselves.