Final answer:
Communicable diseases are easily spread from one person to another, with pathogens including bacteria and viruses being the main cause. They can lead to disease outbreaks and have historical significance, as seen with the Plague of Athens.
Step-by-step explanation:
When a disease becomes communicable, it means that the disease can be easily transmitted from one person to another. Conditions such as the common cold or influenza are examples of communicable diseases that can spread through various means such as air droplets, physical contact, or contaminated surfaces. The spread can occur in different ways, including common source spread, where each infection originates from the same source, or propagated spread, characterized by direct or indirect person-to-person contact where each infected person becomes a source for subsequent infections.
Infectious diseases are a major health concern and can lead to significant events like a disease outbreak, where multiple people contract the disease from a common source of infection. Such diseases are caused by pathogens, which include bacteria, viruses, fungi, and parasites, capable of reproducing within the host's body and causing damage, leading to illness. In history, diseases like the Plague of Athens have demonstrated the devastating effects of infectious diseases and their potential to alter the course of human events.