Infectious Diseases
Infectious diseases are a disorder caused by micro-organisms such as viruses, bacteria, parasites, and fungi, these diseases can be spread, directly or indirectly, from one person to another. They're normally harmless or even helpful, but under certain cases, some organisms may source of disease. Infectious disease results from the coaction between those few microorganisms and the defenses of the hosts they infect. However, a host's immune system can also cause harm to the host itself in an attempt to control the infection.