Week 1 - Infection & Pandemics

Question 1

How does the level of virulence affect the transmission of infections?

Answer 1

Pathogens of low virulence are more likely to infect a greater proportion of the population as pathogens of high virulence lead to people being bed bound and more unwell, thus it cannot travel as quickly.

Question 2

How is the multiplication different for bacteria compared to viruses?

Answer 2

• Bacteria multiply outside of host cells

- Viruses multiply inside host cells

Question 3

What is the difference between exotoxins and endotoxins?

Answer 3

• Exotoxins - proteins produced inside pathogenic bacteria, most gram-positive bacteria, then secreted into surrounding medium following lysis
• Endotoxins - lipid portions of LPSs part of outer membrane of cell wall of gram-negative bacteria, liberated when bacteria die and cell wall breaks apart

Question 4

How do viruses damage tissues?

Answer 4

Viruses are intracellular pathogens and cause cell damage by reproducing inside the cells
Changes in cell include: cell swelling and bursting, cell fusion, carcinogenic changes

Question 5

What are the two internal body defences?

Answer 5

• Innate: inflammatory response carried out by phagocytes within hours
• Adaptive: immune response carried out by lymphocytes after a few days

Question 6

What are the two types of lymphocytes?

Answer 6

• B lymphocytes act in an antibody‐mediated (humoral) immune response
• T lymphocytes act in a cell‐mediated immune response (cellular immunity)

Question 7

What are antigens and antibodies?

Answer 7

• Antigens: large foreign chemicals that stimulate an immune response - are present in viruses, bacteria and other microbes, human and animal cells
• Antibodies: immunoglobulin proteins made by B lymphocytes (B cells) after contact with antigen - inactivate antigens by clumping them together

Question 8

What is Humoral immunity?

Answer 8

Antibody response
It occurs in the body fluids where antibodies attach to specific antigens on microorganisms →leads to clumping of microorganisms → removal by phagocytes

Question 9

What is Cellular immunity?

Answer 9

T lymphocytes (T cells) are activated by antigen contact in cellular immunity
Cytotoxic T cells carry out the cell‐mediated response by – directly killing body cells infected with viruses or other microbes – directly killing some cancer cells

Question 10

What are the different types of vaccines?

Answer 10

• Vaccine: a suspension of • live weakened microbes or
  • dead microbes or • microbe components (acellular vaccine)
• Toxoid: an inactivated bacterial toxin • e.g tetanus, diphtheria

Question 11

What is Herd immunity?

Answer 11

Group immunity – the proportion of the population who are immune to a particular disease
The more immune individuals there are in a population, the less likely it is that a susceptible person will come into contact with someone who has the disease.
Measles need approx 90% immune
Polio approx 80%