A viral infection is a large amount of harmful virus inside the body. A virus cannot produce without a host, so it needs to latch onto a host cell in order to multiply.

Tuberculosis is an air-borne bacterial infection. It most commonly affects the lungs (pulmonary tuberculosis) but in some cases, can also affect other parts of the body (extrapulmonary tuberculosis) like the brain, lymph nodes, joints, bones, and kidneys.

A parasitic infection is an infection that occurs when a parasite enters a body, makes it a host, and causes the host to become sick. Not all parasites can cause a host damage.

Bacterial infections are infections caused by bacteria. They can be mild, severe, or even deadly. Examples of bacterial infections are whooping cough, strep throat, eye infection, and food poisoning.