Infectious diseases occur when the body is infected with an infectious agent that causes disease. The most common contaminants are microorganisms such as bacteria, viruses and fungi.
The treatment of these diseases differs depending on the type of infectious agent. Some diseases caused by viruses can be prevented by vaccine. Vaccine may also alleviate symptoms from an ongoing infection. Diseases caused by bacteria can often be treated with antibiotics, and fungal infections are usually treated with fungicide medicines.
Infectious agents can be spread in many different ways, including through air, direct contact or food and drink. The infectiousness is dependent on the type of microorganism.