Infection 1 - Introduction

Question 1

What is an infection?

Answer 1

Invasion of host’s tissues by micro-organisms + disease caused by microbial multiplication, toxins + the host response.

Question 2

In which ways do people get infections? (3)

Answer 2

1) Physical contact with the source - e.g.: sexually transmitted infections
2) Infected intermediary - e.g.: through a vector, such as mosquito for malaria
3) From environment - e.g.: ingestion of contaminated food or water, inhalation of contaminated air

Question 3

What are the 2 main modes of infectious transmission?

Answer 3

1) Horizontal - e.g.: contact, inhalation + ingestion

2) Vertical - from mother to child, before or at birth

Question 4

How do organisms caused disease?

Answer 4

• Virulence factors - e.g.: exotoxins or endotoxins

- Host cellular damage - direct or as consequence of immune response

Question 5

What are the 2 main determinants of how bad a disease is?

Answer 5

1) The pathogen - e.g.: the virulence factors, inoculum size + any anti-microbial resistance it may have.
2) The patient - e.g.: the site of the infection, and any other co-morbidities that may increase severity of infection.

Question 6

How do we know whether an individual has an infection or not?

Answer 6

1) History - take symptoms + any potential exposures
2) Examination - look for organ dysfunction
3) Investigations - either supportive (e.g.: FBC’s. CRP, blood chemistry etc) to see whether some kind of infection is present + specific (e.g.: antigen detection, culture, microscopy, antibody detection) to find out exactly what the infection is.

Question 7

What is the microbiota?

Answer 7

“Commensal” micro-organisms carried on skin and mucosal surfaces, normally harmless or beneficial, transfer to other sites can be harmful.