The correct answer is a) 1850.
In Western Europe and North America, scientists began to understand the causes of infectious diseases at about 1850.
Scientist in Europe or The United States could better understand the nature of some diseases with the help of better technology and instruments. They started to understand that infectious diseases were disorders caused by organisms. These microorganisms were viruses, bacteria, parasites, and fungi. They understood that these diseases were contagious and could be transmitted by humans, animals, and insects. They also understood the human body reaction to these diseases and the medicine to cure them. For instance, in the mid-1850s, they discovered that Vibrio Cholera was transmitted by contaminated water. The bacteria embeds in the intestinal tract.
The other options of the question were B) 1650, C) 1950, and D) 1750.
