The fact that milk can make you ill has long been recognized. Historically, cultures that milked cows (and to a lesser extent goats and sheep) had practices involved in keeping dairy areas clean to the best of their capabilities. People who have milked animals have always striven to keep the milk as clean and healthy as possible. Doing so of course reduces risk.
This was also seen with cheese making, where sloppy sanitation can cause some really undesirable results. People didn’t know why everything had to be kept so clean, but they were aware of what happened when the cleaning wasn’t done.
Back in the days when dairy herds were smaller the risks were also different. Isolated cows or small groups are much less likely to have “crowd disease” that could be passed on to humans.
In the late 19th Century milk did become a public health risk. Prior to the Industrial Age milk in cities was largely supplied by cows that lived in the city (which had problems, yes, but nothing is perfect). People in cities that desired milk could pick it up directly from the dairy less than half a day out of the cow. This reduced travel time decreased the risks of raw milk by reducing the length of time that bacteria had to replicate. The purchaser could also get a look at how clean the dairy was and get a rough idea of the health of the cow(s). This method still happens in some places, like India. With industrialization there were fewer cows in cities in Europe and milk traveled further distances, which meant longer time between cow and consumer, which meant more bacteria.
If raw milk rarely transmits disease in practice it’s because thousands of years of cultural awareness of the need for cleanliness, and later on germ theory, immunization, and so forth, reduces the risk of raw milk. It is very clear that vigilance is needed, and rules, and inspections to protect the milk supply and prevent illness. Yay, these things usually work.
One reason diseases can pass between bovines and humans more readily than between camels and humans is the longer association between bovines and humans have given pathogens more time to adapt to the companions (humans) of their main host (bovines). That said, it’s not impossible for disease to move between camels and humans, and MERS is a corona virus that can do so. I think we all know at this point that corona viruses are something that can be a problem.
Anything that reduces disease in milk and dairy (of any sort or origin) does have the benefit of reducing disease in both animals and humans, which is a worthy goal.
