C3.2.1 Pathogens as the cause of infectious diseases Notes

Pathogens Can Become Diseases That Infect Humans

1. Before the discovery of pathogens, people believed illnesses were caused by "bad air" or curses.
2. Today, we know that many diseases are caused by microorganisms that invade our bodies.
3. A broad range of disease-causing organisms can infect humans.

What is a Pathogen?

1. A pathogen is a microorganism that causes disease.
2. These tiny invaders can be bacteria, viruses, fungi, protists, or even abnormal proteins called prions.
3. Pathogens are responsible for a wide range of illnesses, from the common cold to life-threatening diseases like Ebola.

Types of Pathogens

1. Bacteria

1. Bacteria are single-celled organisms that can survive in various environments.
2. While many bacteria are harmless or even beneficial, some are pathogenic.
3. Tuberculosis, cholera, and strep throat are examples of bacterial infections.

2. Viruses

1. Viruses are made of genetic material (either DNA or RNA) surrounded by a protein coat.
2. They cannot reproduce on their own, instead, they hijack a host cell's machinery to replicate.
3. Viruses are responsible for a wide range of diseases, such as the flu, HIV/AIDS, and the common cold.

3. Fungi

1. Fungi can be unicellular (e.g., yeast) or multicellular (e.g., molds).
2. Fungi are responsible for infections like athlete's foot, ringworm, and thrush.

4. Protists

1. Structure: Protists are single-celled organisms that can be either free-living or parasitic.
2. Diseases Caused: Malaria, caused by the parasite Plasmodium, is one of the most well-known protist diseases.

How Do Pathogens Cause Disease?

1. Invasion: Pathogens enter the body through various routes, such as the respiratory tract, digestive system, or broken skin.
2. Multiplication: Once inside, they reproduce rapidly. For example, bacteria divide by binary fission, while viruses replicate using host cells.
3. Damage: Pathogens harm the host by:
   1. Producing toxins (e.g., bacterial toxins causing food poisoning).
   2. Destroying cells (e.g., viruses bursting host cells).
   3. Triggering immune responses that damage tissues (e.g., inflammation).
4. Transmission: To survive, pathogens spread to new hosts through coughing, sneezing, direct contact, or vectors like mosquitoes.

Two Observations Leading to Breakthroughs

1. Ignaz Semmelweis and Puerperal Fever

1. In the 19th century, many women died from puerperal fever after childbirth.
2. Ignaz Semmelweis, a Hungarian physician, noticed that doctors who performed autopsies and then delivered babies without washing their hands had higher rates of infection in their patients.
3. By introducing handwashing with chlorinated lime, he dramatically reduced mortality rates.

2. John Snow and Cholera

1. During a cholera outbreak in London, John Snow mapped cases and traced the source to a contaminated water pump on Broad Street.
2. By removing the pump handle, he stopped the outbreak, proving that cholera was waterborne.

Why Understanding Pathogens Matters

1. Prevention and Treatment: Knowing the cause of diseases helps develop vaccines, antibiotics, and antiviral drugs.
2. Public Health: Understanding transmission helps control outbreaks, as seen with COVID-19.
3. Global Impact: Infectious diseases affect millions, influencing economies, societies, and ecosystems.