Module 3 / Lesson 9.1.2
What Do Infectious Agents “Want”?
Infectious agents such as bacteria, viruses, and parasites do not intend to harm us. Just like other creatures, they are shaped by evolutionary forces of natural selection and mutation to survive and reproduce. Understanding their behavior helps explain why infections occur and how these agents interact with our bodies.
Lesson guide
Learning:
- Read the text below to get to know more about "What do infectious agents 'Want'?"
- Watch the video below on disease adaptation and transmission.
Reflection: As you read and watch, think about how the invisible universe of the human microbiome is co-existing with us.
Key Idea: Infectious agents must reproduce inside your body and spread to other bodies to survive.
How do infectious agents work?
1. Survival, Reproduction, and Natural Selection
- Infectious agents depend on your body’s resources to reproduce.
- Through mutation and natural selection, those best at reproducing and spreading become dominant.
- Most microbes are harmless or even beneficial, such as skin flora and gut bacteria.
2. How Infectious Agents Spread
To ensure survival, pathogens must move from one host to another. They have evolved four main transmission modes:
- Airborne: Spread through droplets or aerosols when we cough or sneeze (e.g., COVID-19, flu).
- Waterborne: Spread through contaminated water (e.g., cholera).
- Surface (Fomite) Transmission: Spread when touching contaminated objects such as doorknobs or phones, then touching the mouth or eyes. Hand sanitizers reduce this risk.
- Vector-Borne: Spread through another organism like mosquitoes (e.g., malaria).
3. Why They Make Us Sick
Pathogens cause sickness as part of their survival and reproduction process.
- Using Resources: Microbes take energy and nutrients from the host, causing fatigue and weakness.
- Helping Spread: Some symptoms like coughing, sneezing, or diarrhea help microbes exit the body and infect new hosts.
- Host Defense: The immune system fights infections, producing fever, inflammation, and soreness as side effects of this defense.
4. Microbiome and Friendly Microbes
- Many microbes are beneficial and essential to health.
- They help digest food, produce vitamins, and prevent harmful bacteria from growing.
- Understanding the microbiome is crucial to seeing how not all microbes are enemies.