B10.1 Diseases and immunity

What is a pathogen?

• A disease causing agent, such as:

  • Virus

  • Bacteria

  • Fungi

  • Protist

What is an organism infected by a pathogen called?

Host

What is a vector?

A living organism that transfers a pathogen from one host to another

What is a transmissible disease? 

A disease in which the pathogen can be passed from one host to another

What are examples of transmissible diseases for each type of pathogen?

• Cholera: caused by bacterium

• Athletes foot: caused by fungus

• Malaria: caused by protist

• Common cold: caused by virus

What are the methods of transmission and examples?

• Through direct contact: from blood or through body fluids in sexual intercourse

• Through indirect contact: from the air or through food and drink

Describe the first line of defense in the body against pathogens

• Involves mechanical barriers (structures that prevent pathogens from entering into the body)

1. Hairs in the nose: trap particles carrying pathogens. Ciliated cells in the nose and throat move mucus with these trapped pathogens away from the lungs towards throat.

2. Skin: barrier that prevents the entry of pathogens. If the skin is cut, the blood clots and a scab is formed to prevent blood loss and prevent the entry of a pathogen.

• Involves chemical barriers (substances that trap or kill pathogens)

1. Mucus:

   • Trap dust and pathogens since it is sticky

   • Produced in mucus membranes, inner gut lining and lungs

2. Acid secreted in the stomach:

   • Kills pathogens in food and water we swallow since it is highly acidic because of the HCl it contains

Describe the second line of defense in the body against pathogens

• If pathogens manage to enter the body, the immune system detects and destroys them by using white blood cells.

• White blood cells have different functions, for example:

  • Phagocytes: carry out phagocytosis, process where white blood cell surrounds and engulfs pathogens to destroy it

  • Lymphocytes: produce antibodies, which are proteins that attach to specific pathogens and mark them for destruction

How can you control the spread of disease?

• Clean water supply and sewage treatment

  • Human waste must be separated and sewage needs to be treated to kill pathogens

• Personal hygiene

  • Wash hands, cover when coughing or sneezing, dispose of tissues

• Food hygiene

  • Store food properly, keep meat and dairy refrigerated, cook food thoroughly to kill pathogens

• Waste disposal

  • Food waste needs to be placed in covered containers, waste must be disposed of at a landfill or by burning or composting to avoid attracting insect vectors

• Vaccination

  • Reduce disease spread in population

  • Protect against specific pathogens

State the features of viruses

• They have a protein coat that surrounds genetic material (DNA or RNA)

• They reproduce by inserting their genetic material into the host cell and using the material of the host cells to make more viruses

• They are not living organisms because:

  • Not made of cells

  • Don’t have cell membrane or cytoplasm

  • Don’t have seven characteristics of living organisms (MRS GREN)

What is active immunity?

• Defense against a pathogen by antibody production

• It can be gained naturally (after infection of pathogen) or artificially (vaccination)

What is an antigen?

• Substances (often protein, fats or carbohydrates) that trigger an immune response

• Each pathogen has its own uniquely shaped antigens

What is an antibody?

• Proteins made by lymphocytes that have a specific shape which is complementary to the antigen so that it can bind to it and attack

• After attaching to an antigen, the antibody can either:

  • Mark pathogen for phagocytosis and destruction for phagocytes or

  • Cause pathogen to die by binding to it and causing direct destruction

What are the two types of responses that the immune system has after pathogen infection?

1. Primary response: when the immune system reacts to a pathogen for the first time

2. Secondary response: when the immune system reacts quicker upon reinfection of the same pathogen, this process involves memory cells

What are memory cells?

• Cells that remain in the blood after infection, they remember the specific pathogen

• Upon reinfection, they trigger a fast secondary response which produces antibodies up to 1000x faster than the first time 

  • This destroys antibodies quickly before they cause a disease, giving immunity

Outline the process of vaccination

1. Weakened or dead parts of a pathogen or their antigens (that can no longer cause disease) are put into the body

2. Antigens stimulate an immune response from the lymphocytes, which then produce complementary antibodies and memory cells

3. Memory cells give long term immunity (sometimes a booster vaccination is required)

How do vaccinations prevent the spread of disease?

• Grand herd immunity: when enough people in a population have achieved immunity against a pathogen, making it very difficult to spread the disease