Infectious diseases are often thought of as the kinds of diseases you " catch." The Mayo Clinic further defines infection as a condition that is caused by a living organism, such as bacteria or virus. There are many ways to pass an infectious disease. It can move from person to person, or it can be passed from animals or insects to humans. The Mayo Clinic notes that fever and chills are common symptoms of infectious diseases, but there are a variety of symptoms associated with such conditions. There are vaccines for some infectious diseases, such as flu and chickenpox. Second Opinion has covered a number of infectious diseases, including a special edition on flu during the H1N1 pandemic.