What Are Infectious Diseases?

Infectious diseases are infections transmitted by organisms such as viruses, bacteria, parasites or fungi. These organisms live on or in the human body, where some have beneficial roles, while others cause diseases, according to Mayo Clinic. They spread from through direct contact or indirect contact, and typical examples include measles, respiratory illnesses and malaria, notes Healthline.

The transmission of infectious diseases through direct person-to-person contact occurs when a person touches body fluids of an infected person. Infectious diseases transmitted this way include sexually transmitted diseases and respiratory illnesses. Some sexually transmitted diseases such as gonorrhea pass from the mother to the child during delivery. Infectious diseases also spread through the droplets created when an infected person speaks or through the spray of droplets when sneezing and coughing. Common examples where infectious diseases spread indirectly include airborne transmission and insect bites from organisms that suck blood such as fleas, ticks and mosquitoes, notes Healthline.

Symptoms of these diseases vary depending on the organism that causes them, and typical ones include diarrhea, muscle aches and fever. A person should seek medical attention in case of a cough that lasts for more than a week, if there is unexpected fever, sudden vision or breathing problems, or if an individual has been bitten by an animal, states Mayo Clinic.