L1: An Introduction to Infection

Question 1

What is an infection?

Answer 1

Invasion of host tissue by micro-organism

Question 2

How do infections cause disease?

Answer 2

Microbial Manipulation
Toxins
Host response

Question 3

How do people get infections? (sources)

Answer 3

Patient (self)
Intermediary such as another human
Environment –> contaminated water, air, food, surfaces
Animals –> directly or via environment

Question 4

What do we meant by self infection?

Answer 4

Own microbiota
Normally harmless
Other parts of body –> harmful

Question 5

What do we mean by environment infection?

Answer 5

Contaminated sources
Ingested (food, water)
Inhaled (air)
Contact (surfaces)

Question 6

What do we mean by intermediary infection?

Answer 6

Contact with infected person

• Physical contact –> touching, sexually transmitted
• Airborne
• Vector –> mosquito

Question 7

What are the two modes for transmission?

Answer 7

Horizontal or vertical

Question 8

What do we mean by horizontal transmission?

Answer 8

Source to person

• Contact (direct, indirect, vector)
• Inhalation (droplets, aerosol)
• Ingestion (Food, water, fecal-oral)

Question 9

What do we mean by vertical transmission?

Answer 9

Down the generations

Mother to baby (before, at birth, or after (breast feeding)

Question 10

How do microorganism cause disease?

Answer 10

Exposure
Adherence 
Invasion 
Multiplication 
Dissemination (spread)

Question 11

What are virulence factors? Examples?

Answer 11

Anything that helps a microorganism to survive and replicate
Toxins: Molecules produced by micro-organism to aid them.
-Exotoxins –> released
–> Cytolytic –> breaks cells down
–> AB toxins –> Active binding –> affect
intraculllar processes
–> Superantigens –> excessive activity of
immune system
–> Enzymes
- Endotoxins–> part of –> direct invasion
Adhesion factors
Capsule
LPS
Flagellum
Iron binding protein

Question 12

What types of dissemination are there?

Answer 12

Dissemination = spread
Contiguous spread- local infection 
Hematoguous spread - blood 
Tissue ? - attracted to specific tissue 
Enterovirus - intestinal entrance

Question 13

Once inside the body what do micro-organisms do?

Answer 13

Cellular damage

• Directly
• or by disrupt host immune response

Question 14

What determine whether a micro-organism causes disease?

Answer 14

Pathogen factors
-Virulence factors (molecules produced)
-Inoculation size (amount of micro-organism, threshold must be reached)
- Antimicrobial resistance (resistance to drugs)
Patient factors
- Site of infection
- Co-morbidities –> weaken immune system

Question 15

How can we tell if a patient has an infection?

Answer 15

History (question)
- Symptoms (location, severity, duration)
- Potential exposures (where? what? who with? animals?)
Examination
Investigations
- Specific–> name of organism
- Supportive–> blood count, CRP levels etc..
bacteriology, virology

Question 16

What are supportive investigations?

Answer 16

Investigation –> indicate infection –> not specific

• Full blood count –> WBC levels (neutrophils, lymphocytes, monocytes (macrophages), eosinophils and bsophils), RBC, Hb (O2 carrying), haematocrit (amount of space taken up by RBC in blood), mean corpuscular volume )measurement of average size of RBC)
• C-reactive protein –> inflammation
• Blood chemistry –> liver and kidney function tests
• Imaging –> X-rays etc
• Histophatology (microscopes)

Question 17

What is bacteriology? Methods?

Answer 17

Study of bacteria
- Sample –> Swabs, Fluid, Tissue
- Microscope; bacterial cells (gram+ or -) or patient cells (CSF), Culture (18hr incubation) and Sensitivity tests (antibiotic susceptibility)
- Detect antigens or nuclei acid
Or
PCR –> amplify –> detect by looking at DNA

Question 18

What is virology?

Answer 18

Study of viruses

• Detect antigens –> virus
• Detect antibodies –> body
• Detect vital nuclei acids