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Infectious diseases are illnesses caused by pathogens such as bacteria, viruses, fungi, or parasites. These pathogens can spread from person to person, or from animal to human. Infectious diseases can range from mild, such as the common cold, to severe, life-threatening illnesses such as Ebola, COVID-19, or HIV/AIDS.
Some examples of infectious diseases include:
Prevention and treatment of infectious diseases vary depending on the specific disease, but common strategies to prevent the spread of infectious diseases include:
It is important to seek medical care if you suspect you have an infectious disease, or if you have been in close contact with someone who has one. Early detection and treatment can help prevent the spread of the disease, as well as improve outcomes and reduce the risk of complications.
Infectious diseases can be caused by:
An easy way to catch most infectious diseases is by coming in contact with a person or an animal with the infection. Infectious diseases can be spread through direct contact such as:
Disease-causing organisms also can be passed by indirect contact. Many germs can linger on an inanimate object, such as a tabletop, doorknob or faucet handle.
When you touch a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the germs he or she left behind. If you then touch your eyes, mouth or nose before washing your hands, you may become infected.
Some germs rely on insect carriers — such as mosquitoes, fleas, lice or ticks — to move from host to host. These carriers are known as vectors. Mosquitoes can carry the malaria parasite or West Nile virus. Deer ticks may carry the bacterium that causes Lyme disease.
Disease-causing germs can also infect you through contaminated food and water. This mechanism of transmission allows germs to be spread to many people through a single source. Escherichia coli (E. coli), for example, is a bacterium present in or on certai
Follow these tips to decrease the risk of infection:
Knowing what type of germ is causing your illness makes it easier for your doctor to choose appropriate treatment.
Antibiotics are grouped into "families" of similar types. Bacteria also are put together in groups of similar types, such as streptococcus or E. coli.
Certain types of bacteria are especially susceptible to particular classes of antibiotics. Treatment can be targeted more precisely if your doctor knows what type of bacteria you're infected with.
Antibiotics are usually reserved for bacterial infections, because these types of drugs have no effect on illnesses caused by viruses. But sometimes it's difficult to tell which type of germ is at work. For example, pneumonia can be caused by a bacterium, a virus, a fungus or a parasite.
The overuse of antibiotics has resulted in several types of bacteria developing resistance to one or more varieties of antibiotics. This makes these bacteria much more difficult to treat.
Drugs have been developed to treat some, but not all, viruses. Examples include the viruses that cause:
Topical antifungal medications can be used to treat skin or nail infections caused by fungi. Some fungal infections, such as those affecting the lungs or the mucous membranes, can be treated with an oral antifungal. More-severe internal organ fungal infections, especially in people with weakened immune systems, may require intravenous antifungal medications.
Some diseases, including malaria, are caused by tiny parasites. While there are drugs to treat these diseases, some varieties of parasites have developed resistance to the drugs.