Infection 2: How is infection transmitted

Question 1

How much bacteria do upper airways contain

Answer 1

Saliva 10^8-10^9/ml

Question 2

How much bacteria does GI tract have

Answer 2

Faeces 10^11-10^12/g

Question 3

What does endogenous infection cover

Answer 3

Normal gut flora

Question 4

What is cystitis

Answer 4

Infection of lower urinary tract

Question 5

Symptoms of cystitis

Answer 5

• lower abdominal pain
• urgency to urinate
• dysuria

Question 6

Bacteria causing cystitis

Answer 6

E. Coli: gram-negative bacillus

Question 7

Where do infections come from

Answer 7

• Endogenous infection
• Exogenous infection
• Communicable diseases

Question 8

Sources of exogenous/communicable infection

Answer 8

• person-to-person
• non-human sources
• environment

Question 9

What are the routes of transmission

Answer 9

• Endogenous

- Exogenous

Question 10

What are the endogenous routes of transmission

Answer 10

• migration
• perforation
• blood

Question 11

What are the exogenous routes of transmission

Answer 11

• contact
• injuries
• airborne
• oral
• blood-borne
• sex
• mother-to-baby

Question 12

Explain an example of infection due to migration

Answer 12

• bowel flora, E.Coli, contaminates perineum
• access urethra
• local infection
• Spreads to bladder
• UTI

Question 13

Explain an example of infection due to perforation

Answer 13

• perforation of bowel
• contamination of abdominal cavity with faecal flora
• life-threatening
• sepsis

Question 14

Explain an example of infection spread due to blood spread

Answer 14

• Endocarditis
• dental work —> mouth flora enters blood stream
• circulation —> organisms read distant sites
• invasion occurs, esp. if tissue is abnormal
• inflammation & structural damage

Question 15

Explain a direct contact infection

Answer 15

• impetigo
• superficial skin infection, staphylococci
• spreads rapidly

Question 16

Examples of indirect contact infection

Answer 16

• methicillin-resistant staphylococcus (MRSA)

- norovirus gastroenteritis

Question 17

Infection due to injury

Answer 17

• tetanus
• clostridium tetani
• in soil
• contaminates wounds
• toxin —> muscle spasm
• prevented by vaccination

Question 18

Infection due to bites

Answer 18

• malaria
• mosquitoes & humans
• tropics
• severe febrile illness

Question 19

Airborne infection

Answer 19

• Influenza virus
• coughing & sneezing
• droplets with infectious viruses
• inhaled

Question 20

Oral (food or water-borne) infections

Answer 20

• poor hygiene
• food poisoning
• vomiting, diarrhoea

Question 21

Blood-borne infection example

Answer 21

• Hep B
• liver infection
• viruses spill into blood

Question 22

Transmission by blood exposure

Answer 22

• transfusion
• sharing of needles
• tattoos

Question 23

How is chlamydia risk increased

Answer 23

• unprotected sex
• new partners
• multiple partners
• partners with high risk

Question 24

Examples of mother-to-baby transmission

Answer 24

• pregnancy, rubella
• birth, herpes
• breast milk, HIV
• birth canal, syphilis

Question 25

What ways can HIV be transmitted

Answer 25

- blood borne, injections - vertical, breast milk - sexual

Question 26

How many steps does staphylococcus aureus soft tissues infection take

Answer 26

- 2 - colonisation of of skin: joins skin flora - penetration of skin: spreads&damages

Question 27

What is the Ebola infection mechanism

Answer 27

Direct infection and damage of cells

Question 28

What are virulence factors

Answer 28

- allow invasion of host tissues, streptolysin

Question 29

What do virulence factors do

Answer 29

- lyses cells - cytolysin | - produced by Group A streptococci

Question 30

What does cholera cause

Answer 30

- Severe diarrhoea - massive loss of fluid & electrolytes - dehydration - kidney failure - death

Question 31

What is cholera toxin mechanism

Answer 31

- toxin enters cells of gut lumen —> binges to it - activate adenyl cyclase increasing cAMP - reduces Na+ absorption - increases Cl- secretion

Question 32

What gives rise to antibiotic resistance

Answer 32

- readily mutation - more antibiotics—>more mutations - failure of antibiotic treatment

Question 33

Example where antibiotic resistance causes sever infections

Answer 33

Staphylococcus aureus

Question 34

What are the host factors of infection

Answer 34

- Environment - Barriers to infection - Genetics

Question 35

Environmental factors affecting viral spread

Answer 35

- geography - climate - poverty - public health infrastructure - distribution of infection hosts

Question 36

What dengue fever How is it transmitted What are symptoms

Answer 36

Viral infection Aedes mosquito - fever - rash - muscle pain - bleeding - shock - multi-organ failure

Question 37

What do drugs for stomach ulcer do

Answer 37

Increase pH from 2

Question 38

What are the disadvantages of taking stomach ulcer drugs

Answer 38

Susceptible to food poisoning

Question 39

What’s normal gut bacteria count

Answer 39

10^12/g faeces

Question 40

What does normal gut bacteria do

Answer 40

- prevent colonisation

Question 41

How do pathogens reproduce in gut despite normal gut bacteria

Answer 41

Taking antibiotics harms useful bacteria too

Question 42

Give examples of diseases due to overreaction of immune system

Answer 42

Asthma, arthritis, colitis