L16 & 17 Infection PART 2

Question 1

how much normal microbial flora is there in saliva and in faeces?

Answer 1

saliva - 10^8 - 10^9 bacteria per ml

faeces - 10^11 - 10^12 bacteria per gram

Question 2

where is normal flora found?

Answer 2

skin
gut
upper airways
genital tract

Question 3

what is cystitis?

Answer 3

Infection of lower urinary tract:
Lower abdominal pain
Urgency 
Dysuria
Frequency

Most commonly bacteria from gut flora
E.g. Escherichia coli
E.coli: Gram-negative bacillus

Question 4

what is the difference between an endogenous and an exogenous infection?

Answer 4

endogenous - comes from ourselves

exogenous/communicable - person to person, non-human species eg animals/birds/insects, environment eg soil/water

Question 5

what are the routes of transmission for endogenous infections?

Answer 5

migration
perforation
blood

Question 6

what are the routes of transmission for exogenous infections?

Answer 6

direct/indirect contact
injuries - trauma/bites
airbourne
oral (food/water)
sex
mother to baby (vertical)

Question 7

give an example of an endogenous infection caused by migration

Answer 7

Bowel flora e.g. E.coli contaminates perineum
Gains access to urethra 
Causes local infection
Spreads to bladder (cystitis) and beyond
UTI = Urinary Tract Infection

Question 8

give an example of an endogenous infection caused by perforation

Answer 8

Diseases of bowel especially colon e.g.
Cancer
Diverticular disease
Perforation of bowel wall leads to contamination of abdominal cavity with faecal flora
Severe life-threatening infection results
Faecal peritonitis

Question 9

give an example of an endogenous infection caused by blood spread

Answer 9

Endocarditis:

dental work may allow mouth flora eg streptococci to enter blood stream

Circulation of organisms allows them to reach distant sites e.g. heart valve

Invasion can occur especially if valve tissue is abnormal e.g. congenital defect

Causes inflammation ‘vegetation’ and structural damage

Question 10

give an example of an exogenous reaction caused by direct contact

Answer 10

Impetigo:
superficial skin infection due to staphylococci and/or streptococci
spreads rapidly from person to person

Question 11

give an example of an exogenous reaction caused by indirect contact

Answer 11

Micro-organisms can be transmitted indirectly via hands, equipment, furniture etc
Major route of health-care associated infections

Examples:
methicillin-resistant staphylococcus aureus (MRSA)
Clostridium difficile
Norovirus gastroenteritis

Question 12

what is tetanus?

Answer 12

(lockjaw)
Clostridium tetani - 
Bacterium present in soil
Contaminates wounds
Releases toxin causing muscle spasm
Prevented by vaccination

Question 13

what is malaria?

Answer 13

Parasite infection
Present in large areas of tropics
Causes severe febrile illness affecting all body systems
caused by bite

Question 14

what is the influenza virus?

Answer 14

airbourne infection
Coughing & sneezing
Droplets formed containing infectious viruses
Inhaled by others

Question 15

how are infections spready by oral route - foodbourne?

Answer 15

Food prepared with poor hygiene
E.g. not washing hands after going to toilet
Contaminate food with harmful bacteria
Result: food poisoning!
Vomiting, diarrhoea

Question 16

what is hepatitis B?

Answer 16

hepatitis B virus
Liver infection
Some viruses spill into blood (and other body fluids)
blood-borne infection:
Transfusion
Sharing of needles etc
Tattoos & body piercing

Question 17

how is chlamydia spread?

Answer 17

unprotected sex
new partners
multiple partners
partners with high risk e.g. prostitutes

Question 18

how is vertical transmission mother to baby spread?

Answer 18

During pregnancy e.g. rubella
At time of birth e.g. herpes
Breast milk e.g. HIV

Question 19

what are the 2 steps involved in staphylococcus aureus soft tissue infection?

Answer 19

Step 1: colonisation of skin – joins skin flora

Step 2: penetration of skin – spreads & damages

Question 20

which pathogen factors influence infection?

Answer 20

Infectious dose
Minimum number of organisms required to produce disease
E.g. 18 for norovirus, 108 for cholera

Direct infection of cells/tissues

Virulence factors & toxins
Invasion
Disease

Resistance to antibiotics

Question 21

what is ebola and what are it’s effects on the body?

Answer 21

direct infection and damage or destruction of cells

ebola and marburg virus to macrophage and dendritic cells.

causes tissue damage (liver, spleen, adrenal), systematic inflammatory response, coagulation factors, and impairment of adaptive immunity (no antibodies produced)

Question 22

what are virulence factors?

Answer 22

Allow invasion of host tissues eg streptolysin O
Lyses cells - ‘cytolysin’
Produced by certain streptococci (Group A)

Question 23

what does cholera do to the body?

Answer 23

Severe watery diarrhoea – ‘rice water’
Bacteria  produce toxin
Binds to gut lining cells (mucosa)
Massive loss of fluid and electrolytes
Causes severe dehydration, kidney failure & death

Question 24

what is the cholera toxin mechanism?

Answer 24

Cholera toxin enters cells of gut lumen

Activates adenyl cyclase increasing cAMP

Reduces Na+ absorption

Increases Cl- secretion

Water and other electrolytes drawn into bowel lumen = diarrhoea

Question 25

how does antibiotic resistance occur?

Answer 25

Micro-organisms readily mutate e.g.
HIV, staphylococci

Frequently mutate to escape antibiotic use

More antibiotic use = more mutations

Failure of antibiotic treatment

Question 26

how does the environment contribute to infection?

Answer 26

Geography
Climate
Poverty - Availability of health care e.g. vaccination
Public Health infrastructure - Sanitation
Distribution of other infection hosts - insect or other vectors

Question 27

what is dengue fever?

Answer 27

Virus infection
Transmitted by Aedes mosquito
Fever & rash & muscle pain
Severe form: bleeding, shock & multi organ failure

Question 28

which areas are more at risk of dengue transmission?

Answer 28

south america, some parts of africa, india, and more

Question 29

what are common barriers to infection?

Answer 29

Skin & mucous membranes
Stomach acid
Native bacteria
Immune system
Genetics
Behaviour

Question 30

how could infections arise from cuts/abrasions?

Answer 30

cuts = wound infections 
abrasions = conjunctivitis

Question 31

what is pH of stomach acid, and how do drugs treat stomach ulcers?

Answer 31

Hydrochloric acid - pH 2
Very few organisms survive this

Commonly used drugs for stomach ulcer increase pH

Patients taking these are more susceptible to food poisoning E.g. Campylobacter from poorly cooked chicken

Question 32

what is the role of normal flora and how do drugs affect this?

Answer 32

Prevent colonisation by pathogenic (disease-causing) bacteria
Antibiotic treatment destroys the normal ‘friendly’ bacteria
This allows the pathogens (‘bad’ bacteria) to reproduce & cause disease
E.g. diarrhoea due to clostridium difficile

Question 33

how could the immune system be damaged?

Answer 33

Cancers
Chemotherapy damages the immune system

Diseases due to overactive immune systems ‘autoimmune’
Asthma, types of arthritis, bowel inflammation ’colitis’
Usually treated by drugs which make the immune system less active e.g. corticosteroids

Question 34

how does HIV affect the immune system?

Answer 34

Infects white cells which control immune system
Makes most infections commoner & more severe
Causes infections by micro-organisms which don’t usually cause harm
‘opportunistic infection’

Question 35

how can genetic defects protect against infection?

Answer 35

eg. Sickle cell disease (abnormal red cells) heterozygotes are protected against malaria

Question 36

which behaviours could increase infection risk?

Answer 36

Occupation
Travel
Recreation
Sex
Drugs
Contacts - Friends and pets