Infection is any illness or condition caused by germs (such as bacteria, viruses, fungi, or parasites) that invade and grow in the body. These germs may cause symptoms like fever, headache, and sickness. Some infections are more serious than others.
Bacteria are single-celled organisms that live in and on the human body and almost everything else. Most bacteria do not cause infections and are helpful to the body. But some bacteria can make you sick, especially if they get into places they shouldn’t be, such as your skin, gut (GI tract), lungs, heart, or blood. Harmful bacteria can spread disease by direct contact with infected people or animals, or with contaminated surfaces. Some bacteria are carried by bugs, such as mosquitoes and ticks that can spread Rocky Mountain spotted fever, Lyme disease, and shigellosis. Other bacteria are spread through food, water, or air contamination.
Viruses are small packets of genetic material (RNA or DNA) surrounded by a coat of proteins and fatty molecules called lipids. They don’t have the raw materials to reproduce on their own so they infect cells and take over the cell’s function, making it produce new viruses. Viruses can also spread by touching infected people or objects.
Fungi are spore-forming organisms that range from yeast that causes bread mold to the fungus behind athlete’s foot and ringworm. Some fungi cause infections that can be very serious, such as histoplasmosis and pulmonary tuberculosis. Others cause only minor skin infections or rashes. Parasites include protozoa (including the agents behind malaria and amoebiasis) and helminths (parasitic worms such as hookworm, whipworm, and schistosomiasis).
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