Infection 2: How is infection transmitted Flashcards
How much bacteria do upper airways contain
Saliva 10^8-10^9/ml
How much bacteria does GI tract have
Faeces 10^11-10^12/g
What does endogenous infection cover
Normal gut flora
What is cystitis
Infection of lower urinary tract
Symptoms of cystitis
- lower abdominal pain
- urgency to urinate
- dysuria
Bacteria causing cystitis
E. Coli: gram-negative bacillus
Where do infections come from
- Endogenous infection
- Exogenous infection
- Communicable diseases
Sources of exogenous/communicable infection
- person-to-person
- non-human sources
- environment
What are the routes of transmission
- Endogenous
- Exogenous
What are the endogenous routes of transmission
- migration
- perforation
- blood
What are the exogenous routes of transmission
- contact
- injuries
- airborne
- oral
- blood-borne
- sex
- mother-to-baby
Explain an example of infection due to migration
- bowel flora, E.Coli, contaminates perineum
- access urethra
- local infection
- Spreads to bladder
- UTI
Explain an example of infection due to perforation
- perforation of bowel
- contamination of abdominal cavity with faecal flora
- life-threatening
- sepsis
Explain an example of infection spread due to blood spread
- Endocarditis
- dental work —> mouth flora enters blood stream
- circulation —> organisms read distant sites
- invasion occurs, esp. if tissue is abnormal
- inflammation & structural damage
Explain a direct contact infection
- impetigo
- superficial skin infection, staphylococci
- spreads rapidly
Examples of indirect contact infection
- methicillin-resistant staphylococcus (MRSA)
- norovirus gastroenteritis
Infection due to injury
- tetanus
- clostridium tetani
- in soil
- contaminates wounds
- toxin —> muscle spasm
- prevented by vaccination
Infection due to bites
- malaria
- mosquitoes & humans
- tropics
- severe febrile illness
Airborne infection
- Influenza virus
- coughing & sneezing
- droplets with infectious viruses
- inhaled
Oral (food or water-borne) infections
- poor hygiene
- food poisoning
- vomiting, diarrhoea
Blood-borne infection example
- Hep B
- liver infection
- viruses spill into blood
Transmission by blood exposure
- transfusion
- sharing of needles
- tattoos
How is chlamydia risk increased
- unprotected sex
- new partners
- multiple partners
- partners with high risk
Examples of mother-to-baby transmission
- pregnancy, rubella
- birth, herpes
- breast milk, HIV
- birth canal, syphilis
What ways can HIV be transmitted
- blood borne, injections
- vertical, breast milk
- sexual
How many steps does staphylococcus aureus soft tissues infection take
- 2
- colonisation of of skin: joins skin flora
- penetration of skin: spreads&damages
What is the Ebola infection mechanism
Direct infection and damage of cells
What are virulence factors
- allow invasion of host tissues, streptolysin
What do virulence factors do
- lyses cells - cytolysin
- produced by Group A streptococci
What does cholera cause
- Severe diarrhoea
- massive loss of fluid & electrolytes
- dehydration
- kidney failure
- death
What is cholera toxin mechanism
- toxin enters cells of gut lumen —> binges to it
- activate adenyl cyclase increasing cAMP
- reduces Na+ absorption
- increases Cl- secretion
What gives rise to antibiotic resistance
- readily mutation
- more antibiotics—>more mutations
- failure of antibiotic treatment
Example where antibiotic resistance causes sever infections
Staphylococcus aureus
What are the host factors of infection
- Environment
- Barriers to infection
- Genetics
Environmental factors affecting viral spread
- geography
- climate
- poverty
- public health infrastructure
- distribution of infection hosts
What dengue fever
How is it transmitted
What are symptoms
Viral infection
Aedes mosquito
- fever
- rash
- muscle pain
- bleeding
- shock
- multi-organ failure
What do drugs for stomach ulcer do
Increase pH from 2
What are the disadvantages of taking stomach ulcer drugs
Susceptible to food poisoning
What’s normal gut bacteria count
10^12/g faeces
What does normal gut bacteria do
- prevent colonisation
How do pathogens reproduce in gut despite normal gut bacteria
Taking antibiotics harms useful bacteria too
Give examples of diseases due to overreaction of immune system
Asthma, arthritis, colitis
