Infection is when germs — like bacteria or viruses — enter your body and multiply. Disease happens when the germs damage your cells and cause you to feel sick. Most infections clear up with medicine, but some may be more serious. Your immune system goes to work to fight the infection. You might have symptoms like fever, rash or fatigue while the white blood cells and antibodies go to work to destroy the germs.
Bacteria are microscopic single-celled creatures that have been around for 3.5 billion years. They live in the environment and can survive extreme heat and cold, radiation and even radioactive waste. Only about 1% of bacteria cause diseases in people. When they do, it’s often because they get into places they’re not supposed to be (like your mouth, nose or eyes) and reproduce quickly, or because they release toxins that damage cells. You can get bacterial infections by direct contact with the skin or mucous membranes, or indirectly through contaminated food and water. You can also catch some bacterial diseases from being bitten by an infected insect or tick, such as Lyme disease or Rocky Mountain spotted fever.
Viruses can infect many different parts of your body, including the respiratory and digestive tracts, and the nervous and immune systems. Some types of viruses are spread from person to person, such as influenza and herpes B. Others are spread from animals, such as rabies and hepatitis A. Still others are spread through contaminated water or food, such as E. coli, Campylobacter and Salmonella, or by touching something that contains the germs and then touching your mouth, nose or eyes (for example, giardiasis).