An infectious disease is one that's caused by another organism, typically a germ. Germs can be many different types of organisms, including viruses, bacteria, fungi and protozoa. Infectious diseases are often passed from one person to another, and they also can be spread through contaminated food, soil and water, as well as insect or animal bites.
There are a wide variety of infectious diseases, ranging from some that are a mild inconvenience to others than are life-threatening conditions. Colds and flu, for example, are infectious diseases caused by viruses. HIV/AIDS is also an infectious disease caused by a virus. People can get sick from bacteria like salmonella found in contaminated food. Bacteria can also be passed along by sexual contact, causing diseases such as chlamydia and gonorrhea. These are just a few of the many different infectious diseases that people can develop.
Some infectious diseases are easier to spread among humans than others. A cold virus, for example, can be obtained very easily by breathing air that contains the virus. The HIV virus, on the other hand, is typically passed only through sexual contact or contact with contaminated blood.
The primary way to protect against infectious diseases is to practice good hygiene. This includes washing hands frequently and avoiding contact with contaminated items. To avoid contracting sexually transmitted diseases, condoms should be used during sex and people should avoid having sex with those who are infected. It's also important to not share such things as drugs needles, toothbrushes, razors and other personal items, as sharing these items can also spread infectious diseases.
Vaccinations have helped immensely in preventing the spread of infectious diseases in the United States and other parts of the world. Rates of diseases such as measles, mumps, rubella, whooping cough and many others have dropped substantially in the United States thanks to the widespread use of vaccinations against these diseases.
SOURCES: U.S. National Library of Medicine; World Health Organization; U.S. Centers for Disease Control and Prevention; KidsHealth, Nemours Foundation