Pathogens (bacteria and viruses that cause disease) can enter the body through various passages. Skin provides good protection against entry from pathogens so your vulnerable areas are your eyes, nose, mouth, ears and open wounds. Your (unwashed) hands can deliver pathogens to these areas.
Airborne pathogens will enter through the mouth or nose as you breath them in.
Pathogens in food will enter through your mouth into your digestive system.
Pathogens can also enter through "vectors" directly into the blood stream - through mosquitos, fleas, ticks or contaminated needles, for example.
for example is the pathogen that causes Lyme disease. Broadly, this includes non-living (or gray area) agents that can replicate in a host, such as prions and viruses. So varicella zoster is a pathogen that causes chicken pox and shingles. Herpes simplex viruses cause a list of diseases. Staphylococcus aureus is another pathogen that can cause a range of diseases, from mild to severe and life-threatening.