So in a lot of developed cities and in rural places all over the world encountering a couple rodents in a subway station or in the barn is not at all unusual even if personally or economically undesirable and is generally handled by the city or the farmer as just the cost of living life or doing business - and lots of people in the country regard a barn cat or two as sufficient, regardless of how questionable the net effect of that is. But a rodent in the house is something that needs to be more or less immediately dealt with, possibly by an expensive professional depending on the severity, local health concerns (my region of the U.S. is home to hantaviruses and the plague), and homeowner's proclivities.
But I imagine this wasn't always the case and one point rodents in the home could be expected as normal part of life, even if never exactly desirable (like how most people don't freak out or even care if a moth is fluttering around, especially if they don't have any fur or cashmere clothes). So when did that change? And does it have any relation to public awareness of modern germ theory or were they separate developments?
Thanks!
Oh, this is a fantastic question that's really difficult to answer. There's a couple sub-questions here, I'm going to do my best at putting together some answers, but there's no one answer to cover it all. The very very short summary: it's probably most accurate to say that it began to change towards the end of the industrial revolution, with the rise of the Sanitary Movement. That change coincided with the rise of germ theory, however, they largely evolved separately.
Very short answer 1: There is some evidence, dating back to Babylonia in the 19th century BCE that it was known dogs could develop a condition of "madness" which could be transmitted to humans, and that's almost certainly talking about rabies. At its most basic level, we have had the idea that a condition can be transmitted from animal to human for thousands of years. There has been a public health imperative to control rodent and other pest populations for as long as humans have had agriculture: rodents in your grain stores means rodent feces in your grain stores, and also, less grain for you and your family.
Very short answer 1.5: Rats probably weren't as much of a causative factor in the Black Death as they are widely considered to; many historians think there just weren't enough rats and there were many other carriers. Rats were a major cause of the 1994 plague outbreak in India, which is a big part of what has cemented the narrative. Rats also carry all sorts of diseases,
Very short answer 2: The scientific concept zoonoses (disease transmission from animal to human) was not formalized until Rudolf Virchow coined the word in the 1870s. Virchow was an interesting guy, a very brilliant pathologist to whom modern medicine owes a great deal, and he was an early advocate for what is now called "social medicine". He saw a clear link between unsanitary living conditions and disease. One could argue that the public health imperative for pest control largely began with Virchow. Shortly thereafter, in the late 1800s, a number of zoonotic diseases were identified, including bovine TB, anthrax, and ringworm (aka dermatophytosis, aka athlete's foot/jock itch). We were able to identify the causative agent, see under a microscope that it looked the same from both humans and animals, and trace the transmission in cases back to an animal source.
Very short answer 3: Virchow was a bit of a swing and a miss, because while he understood that animals could in some manner transmit diseases to humans, he vehemently denied that any sort of external pathogen was involved. It seems confusing to a modern reader, but keep in mind that microscopy was brand new; we had just developed the technology to see things at a cellular level, and had spent eons running with theories like miasma theory and the four humors. He gets a lot of credit, but always with an asterisk, because he was still missing a bit part of the story.
Very short answer 4: Again, rodents have pretty much always been considered pests, and starting in the 1830s -- so before Virchow and Pasteur did their things -- people like Edwin Chadwick in the UK were starting the Sanitary Movement, which essentially said, "perhaps people will be healthier if they are not living in literal sewage and garbage." They were still working from miasma theory, that disease was caused by "bad air", which was in turn caused by any number of factors including humidity/dampness, human waste, garbage, and the weather. It took a long time to fully get rid of miasma theory, and in all fairness, in the context of the Sanitary Movement, it wasn't exactly wrong. Living with garbage in the streets is a cause of disease; they were just missing some pieces of the puzzle like animal reservoirs and pathogens.
I hope this helps! Like many things in the history of public health, it's tricky to answer, because a lot of things happened in parallel and not in a tidy, linear order.
Some sources:
The Sanitarians: A History of American Public Health by John Duffy ISBN 0252062760
Deadly Companions: How Microbes Shaped Our History by Dorothy H Crawford ISBN 0199561443
Zoonoses-With Friends Like This, Who Needs Enemies (this has the greatest disclosure of conflict of interests I've ever seen in my life).
A history of Zoonoses and Sapronoses and Research Into Them
The History of Rabies in the Western Hemisphere
The Evolution of Epidemiological Thinking
LOCAL INTELLIGENCE.; Moving Day and the Weather. Will some Pied Piper Appear? Foreign Missions of the Presbyterian Church. The New York Times, May 2, 1865 (I can "gift" this article to up to 10 people, let me know if you're interested).