Pathogen definitions

Infection and Response

Communicable vs. Non-Communicable Diseases

• Communicable Diseases:

  • Can be transmitted from one person to another.

  • Examples: Measles, mumps, rubella, malaria.

• Non-Communicable Diseases:

  • Cannot be transmitted from one person to another.

  • Examples: Cancer, heart attack, diabetes, asthma.

Pathogens

• Definition: Infectious agents that cause disease.

• Types:

  • Bacteria

  • Viruses

  • Protists

  • Fungi

  • Prions

  • Parasites

Types of Pathogens

• Cellular (Living):

  • Protozoa (e.g., plasmodia) \rightarrow Malaria

  • Fungi (e.g., tinea) \rightarrow Athlete's foot

  • Prokaryote (i.e., bacteria) \rightarrow Leprosy

  • Parasites

    • Tapeworm

• Acellular (Non-Living):

  • Virus (e.g., HIV) \Rightarrow AIDS

  • Prion \rightarrow CJD

Features of Bacteria

• Prokaryotes: Single-celled organisms.

• Lack a true nucleus; have a circular strand of DNA.

• Do not contain mitochondria.

• May possess a flagellum (tail) for movement.

• Produce toxins that damage cells and tissues.

• Living cells.

• Size: Up to 10 micrometres long.

• Examples: Lactobacillus, Salmonella, Staphylococcus.

Features of Viruses

• Not cells.

• Much smaller than bacteria.

• Reproduce rapidly inside host cells.

• Composed of genetic material and a protein coat.

• Replication process: A virus invades a cell, makes thousands of copies of itself, and then the cell bursts open, which causes damage making humans feel unwell.

• Examples of diseases caused by viruses: Measles, mumps, chicken pox, colds.

Features of Protists

• Eukaryotes: Single-celled organisms.

• Can be parasitic, living on or inside another organism, causing harm.

• Diverse: Can be animal-like, plant-like, or fungi-like.

• Example: Malaria, transmitted by mosquitos.

Life Cycle of Malarial Protists

1. A healthy person is bitten by an infected mosquito.

2. The parasite is injected into the bloodstream.

3. The parasite invades the liver and red blood cells, causing the illness.

4. If a mosquito feeds on the blood of an infected person, the parasite enters the mosquito.

5. When the mosquito feeds on a healthy person, the parasite is passed on.

Features of Fungi

• Examples of multi-cellular fungi: Toadstools, mushrooms, and moulds.

• Cell wall is made from chitin.

• Saprotrophic nutrition: Secrete enzymes to digest food and then absorb it.

• Possess thread-like structures called hyphae.

• Hyphae can produce spores, facilitating easy spread.