When people weren't aware of bacteria and viruses what was their understanding of infectious diseases?

Answer 1

Generally speaking, before the germ theory of disease, and other advances in modern medicine (genetics, pathology, physiology, etc.) the supposed etiology (cause) of disease was hotly debated throughout history and varied greatly over time and between cultures.

To answer this more specifically, you would want to define the location, culture, and time period.

However, common beliefs about the source of diseases included:

1. Religious and spiritual beliefs were commonly used to explain why someone developed disease. This was highly specific to the culture and time period, but generally speaking, according to this model, a person got sick because they did something bad, committed a sin, upset a God, disrespected an ancestor, violated a religiously dictated law, etc.
2. Air quality or breathing in contaminated air. In fact, the word "malaria" is derivted from the Italian 'mal'aria' meaning "bad air"
3. The ancient Greeks and Romans purposed a system called Humorism. According to this (now antiquated) theory, all humans are made up of four humors: Phlegm, Blood, Black Bile, and Yellow Bile. Healthy individuals had a 'correct balance' of the four humors, whereas having too much or not enough of one or more of the humors would lead to disease.
4. This is also highly specific to different cultures, but a common theme throughout history was that other people caused disease by being different or unclean. For example, when one society mixed with another, often one group would spread a disease that they had immunity to because it was common in their society, but was brand new to the other culture. Instead of attributing this to bacteria, viruses, or herd immunity it was attributed that other group being "unclean".