1) Communicable Diseases

Types of Pathogens

1. Pathogens:

   • Microorganisms that enter the body and cause disease.

   • Responsible for communicable diseases (infectious diseases that spread easily).

   • Infect both plants and animals.

2. Bacteria:

   • Very small living cells, about 1/100th the size of human body cells.

   • Reproduce rapidly in the body.

   • Cause illness by producing toxins that damage cells and tissues.

3. Viruses:

   • Not cells; they're about 1/100th the size of bacteria.

   • Also reproduce rapidly in the body.

   • Live inside cells, using the cells’ machinery to replicate and eventually causing the cell to burst, releasing new viruses.

   • Cell damage from viral reproduction makes you feel ill.

4. Protists:

   • Single-celled eukaryotes (cells with a nucleus).

   • Some are parasites, living in or on other organisms and causing damage.

   • Often transmitted by a vector (organism that carries the protist without getting infected itself, e.g., insects).

5. Fungi:

   • Can be single-celled or made up of hyphae (thread-like structures).

   • Hyphae can penetrate human skin and plant surfaces, causing disease.

   • Fungi can produce spores that spread to other organisms.

How Pathogens Spread

1. Water:

   • Some pathogens are spread through contaminated water.

   • Example: Cholera is a bacterial infection spread through water contaminated by diarrhea from infected people.

2. Air:

   • Pathogens can travel in air droplets, particularly when an infected person coughs or sneezes.

   • Example: Influenza virus spreads this way.

3. Direct Contact:

   • Spread by touching contaminated surfaces, including skin.

   • Example: Athlete's foot, a fungal infection, spreads by contact with shared surfaces like shower floors or towels.