For rain and very light snow, 2WD will likely work fine, and for most vehicles, front-wheel drive is the preferred setup. (For performance cars, RWD is preferred, but AWD, if available, can increase traction. AWD is fine for most normal snow conditions or for light-duty, off-pavement excursions.
Microorganisms that cause diseases are called pathogens. They are specialised to infect body tissues where they reproduce and cause damage that gives rise to the symptoms of the infection. The body fights back by mobilising its immune system to fight off the infection.
Infectious diseases are caused by small microbes invisible to the eye. The microbes include bacteria, protozoans, fungi, yeast and virus. Of them bacteria and protozoans are the most common disease causing agents. Bacteria cause disease both in plants and animals.