L5- Spread of microbial infection

Question 1

What 3 things are needed for an infection to spread?

Answer 1

• Source of pathogen
• Susceptible host
• Means of transmission

Question 2

What factors increase the risk of infection in a host?

Answer 2

• Immune status being weak
• Damage to human tissue, skin or membranes
• Age
• Comorbidities

Question 3

What means does transmission occur by?

Answer 3

• Entry to body e.g skin, oral cavity, respiratory tract

* Vertical or horizontal mode of transmission

Question 4

What is vertical and horizontal transmission?

Answer 4

Horizontal= transmission among individuals of the same generation, rapid, e.g polio, influenza, typhoid

Vertical= transmission from mothers to offspring, slow, e.g HTLV, HIV, cytomegalovirus

Question 5

How does airborne respiratory infection occur?

Answer 5

• Aerosols are clouds of droplets suspended in the air
• Droplets larger than 5um get trapped in upper RT
• Droplet nuclei are the residual of the droplets and often contain pathogens
• Are smaller than 5um so can be inhaled into lower RT

Question 6

Which respiratory tract infections spread via droplet nuclei?

Answer 6

• Bacterial= diptheria, TB

* Viral= flu, MMR, rhinovirus

Question 7

How can airborne spread be reduced?

Answer 7

• Limiting exposure by hand washing, vaccination and isolation
• Personal protective equipment like face masks, room ventilation control

Question 8

What does the larynx do?

Answer 8

Functions to permit the air alone to pass into the lungs and forms boundary between upper and lower respiratory tract

Question 9

What are the two zones in the human lung?

Answer 9

1. Conducting- passageway for gases, trachea to terminal bronchioles
2. Respiratory- gas exchange, respiratory bronchioles to alveolar sacs

Question 10

What are the common microbes found in the respiratory tract?

Answer 10

• Oral streptococci
• Neisseria S.B.
• Haemophilus influenzae

Question 11

What are the occasional microbes found in the respiratory tract?

Answer 11

• Streptococcus pneumoniae

* Neisseria meningitidus

Question 12

What are the uncommon microbes found in the respiratory tract?

Answer 12

• Corynebacterium diptheria
• E. coli
• C. albicans

Question 13

What are physical barriers to pathogens?

Answer 13

• Vibrissae (nasal hairs) filter out many particles

* Mucociliary clearance removes microbes and particles in the nasal cavity and other ciliated areas

Question 14

What are antimicrobial substance defences?

Answer 14

• Lysozyme- hydrolyses bacterial peptidoglycan molecules in their cell walls
• Lactoferrin complexes iron to hinder microbial growht
• Secretory IgA impairs bacterial adherence and agglutinates

Question 15

What are the defences in the lower respiratory tract?

Answer 15

• Alveolar macrophages important in defence- secreting antimicrobials (lysozymes, proteases, oxygen metabolites, phagocytosis)

Question 16

What are the ways in which microbes get around the defences?

Answer 16

• Ciliostatic factors
• Tracheal cytotoxins (neisseria)
• Avoiding/incomplete alveolar phagocytosis (Strep. pneumoniae, T.B.)
• Adherence to respiratory sites (S. pneumoniae)
• Cleavage of IgA (P. aeruginosa)

Question 17

What is the infectious dose?

Answer 17

Number of microbes needed to cause an infection

Lower the number, the easier the infection develops

Question 18

What are common types of respiratory infections?

Answer 18

• Common cold
• Pneumonia
• Diptheria- corynebacterium diptheriae
• Tuberculosis- myobacterium tuberculosis
• Whooping cough- bordetella pertussis