Introduction to Infectious Diseases

This section introduces the biological and evolutionary foundations of infectious diseases, the living agents that inhabit and spread between humans and other organisms. This sub-lesson explains what infectious agents are, why they behave as they do, and how their relationship with animals (including humans) has evolved over millions of years.

By understanding these principles, we gain insight into how infections emerge, why most microbes are harmless or even helpful, and why certain ones occasionally cause disease outbreaks.

In This Lesson

We will explore three key topics:

1. 9.1.1 What Are They? Types of Infectious Agents
2. 9.1.2 What Do They “Want”?

3. 9.1.3 Co-evolution of Animals and Infectious Diseases

4. 9.1.4: Infectious Diseases as Weapons