MICRO - GIT Infections Flashcards
1
Q
gastroenteritis ‘definition’ + Sx
A
- general disease characterised by N/V/D, abdominal discomfort
2
Q
diarrhoea ‘definition’ + Sx
A
- abnormal faecal discharge characterised by frequent and/or liquid stool
- usually small intestine
- usually related to enterotoxin
3
Q
dysentery ‘definition’ + Sx
A
- inflammatory disorder (usually large intestine), usually invasive infection with mucosal obstruction
- blood and pus in faeces
- pain, fever, abdo cramps
4
Q
2 types of salmonella + transmission
A
- enteric fever: typhi and paratyphi (no animal reservoir - only human-human transmission via contaminated food/water), much easier to become systemic
- non-typhoid: mostly acute but self-limiting diarrhoea, can be invasive (sepsis), have large animal reservoirs - transferred via contaminated food, large infectious dose required
5
Q
Dx and Tx of salmonella (non-typhoid)
A
- Dx: culture on selective media or PCR, blood cultures if suspect bacteraemia
- Tx: usually self-limiting, fluid + electrolytes, NO ANTIBIOTICS (doesn’t reduce Sx or illness duration, may prolong excretion of bacteria)
6
Q
salmonella pathogenesis
A
- invades M cells and picked up by macrophages in Peyer’s patches
- multiply in the macrophage and end up in bloodstream = bacteraemia and spread to multiple organs
- can also spill out again once they’ve gone to other organs = secondary bacteraemia
7
Q
enteric fever (typhoid and paratyphoid salmonella) Sx
A
- fever, malaise, aches
- diarrhoea, constipation
- rose spots are characteristic in half of the Pts
8
Q
Dx, Tx, prevention for enteric fever (typhoid salmonella)
A
- Dx: stool AND blood culture
- Tx: immediate antibiotics
- prevention: vaccination
9
Q
- which E. coli strain is the ‘traveller’s diarrhoea’?
- which strain causes dysentery as opposed to diarrhoea?
A
- traveller’s diarrhoea: enterotoxigenic E. coli (ETEC)
- enteroinvasive E. coli (EIEC): dysentery
10
Q
infectious dose required to get E. coli infection
A
- large dose (>10^5)
11
Q
shigella (bacillary dysentery)
- aetiology
- transmission
- how infectious
A
- aetiology: from mild to severe = S. sonnei, S. flexneri, S. boydii, S. dysenteriae
- transmission: faecal-oral route (no animals), primarily paediatric
- VERY infectious (<10 organisms to cause disease)
12
Q
shigella Sx
A
- Sx range from mild to severe gastroenteritis depending on species
- watery diarrhoea at first, later contains mucus and blood
- may have lower abdo cramps
13
Q
shigella pathogenesis
A
- invades colonic mucosa = inflammation and ulceration
- S. dysenteriae = shiga toxin which can damage glomerular endothelium = kidney failure
14
Q
Dx and Tx of shigellosis
A
- Dx: culture or rapid molecular tests
- Tx: rehydration, antibiotics for severe cases
15
Q
campylobacter jejuni
- transmission
- how infectious is it
- pathogenesis
A
- transmission: large animal reservoir, transmitted by contaminated chicken, dairy, water
- highly infectious + microaerophilic (doesn’t need lots of oxygen) and thermophilic (grows well at high temps)
- pathophys: invades mucosal surfaces in jejunum, ileum and colon = ulceration and inflamed bleeding. cytotoxins can cause bacteraemia esp. if immunocompromised
16
Q
Sx and Tx for Campylobacter jejuni
A
- Sx: diarrhoea
- Tx: usually self-limiting, antibiotics if invasive
17
Q
cholera
- transmission
- how infectious is it
- Sx
A
- transmission: spread via contaminated food/water, only human-human transmission (can have asymptomatic carriers)
- high infectious dose needed
- Sx: severe, watery, non-bloody diarrhoea (rice water stool) = massive fluid loss and electrolyte imbalance = high mortality if untreated
18
Q
cholera pathophys + Dx
A
- cholera enterotoxin = not very invasive = tricks intestinal epithelium to have a mass exodus of electrolytes
- Dx: culture (selective + differential media) but can also do PCR
19
Q
cholera Tx
A
- oral or IV fluids
- antibiotics (e.g. tetracycline, azithromycin) to reduce duration of infection and diarrhoea - if moderate to severe dehydration
- killed whole-cell vaccine (only 50% effective and protective for 3-6 months)
20
Q
antibiotic-associated diarrhoea
- aetiology
- pathogenesis
- 2 toxins involved
A
- C. difficile
- pathogenesis: antibiotics disrupts normal flora = C. difficile can multiply
- toxin A (enterotoxin) = increased intestinal permeability and fluid secretion
- toxin B (cytotoxin) = colonic inflammation, haemostasis and colon necrosis
21
Q
Sx, Dx, Tx of C. difficile infection
A
- Sx: diarrhoea, abdo pain, fever (after antibiotic Tx)
- Dx: detection of toxin in stool
- Tx: anti-anaerobic (e.g. metronidazole) or oral vancomycin, can also do faecal microbiota transplant (FMT)
22
Q
food poisoning vs food-borne infections
A
- food poisoning = consumption of food containing pre-formed toxins, fast onset
- food-borne infections = food is a vehicle for a pathogen to multiply in our bodies once the food is eaten
23
Q
S. aureus food poisoning pathophys + Sx
A
- up to 50% of S. aureus produces enterotoxin = heating kills bacteria but not toxin (many ppl carry bacteria on skin and nose)
- Sx: fast onset (<6 hrs) and usually self-limiting vomiting (no diarrhoea)
24
Q
bacillus cerus food poisoning
- pathogenesis
- 2 forms
- common cause
A
- produces spores (found in soil and food) which survive cooking and germinate further on cooling
- emetic form: rapid onset vomiting due to preformed toxin in food
- diarrhoeal form: watery diarrhoea due to enterotoxin production in gut
- commonly occurs due to rice not properly stored after cooking
25
botulism food poisoning pathophys
- toxin ingested in food (usually canned food) and absorbed into bloodstream
- reaches peripheral nerve synapses and causes symmetrical descending flaccid muscle paralysis
26
C. perfringens food poisoning pathophys + Sx
- pathophys: enterotoxin sits in spore-contaminated or inadequately cooked food
- Sx: abdominal pain, diarrhoea (usually self-limiting), necrotising disease of small bowel (if severe)
27
H. pylori
- transmission
- Sx
- complication
- spread from person-person via contaminated food or water (50% of ppl have in normal flora)
- Sx: usually asymptomatic but can cause dyspepsia, upper abdo pain, nausea, burping, bloating
- can cause gastric ulcers and cancers
28
H. pylori Dx and Tx
- Dx: urea breath test, faecal antigen testing, endoscopy with biopsies, PCR
- Tx: PPIs and antibiotics
29
H. pylori pathophys
- urease enzyme breaks down urea into NH3 and CO2 = increased stomach pH = protects itself against gastric acid
- also stomach mucus becomes much thinner so H. pylori can use flagella to swim to epithelium
30
norovirus
- transmission
- how infectious is it
- Sx
- Dx
- is there a vaccine?
- transmission: persists on surfaces and food or water-borne, contaminated shellfish e.g. cruise ships, aged care homes
- highly infectious
- Sx: N/V/D, abdo pain, projectile vomiting (1-2 day recovery)
- Dx: PCR, electron microscopy, ELISA
- no vaccine
31
rotavirus
- transmission
- pathophys
- who is likely to get it
- Sx
- transmission: faecal-oral route
- pathophys: damages transport mechanisms in the gut = diarrhoea (no inflammation or blood loss)
- most common in kids <2 yrs (IgA antibodies protect them for the first 6 months)
- Sx: fever, vomiting and diarrhoea, can have cough and coryza
32
rotavirus
- Dx
- Tx
- is there a vaccine
- Dx: PCR or antigen detection
- Tx: no antivirals
- oral vaccine exists
33
which hepatitis can only occur in patients already infected with Hep B?
- hep D
34
which hepatitis viruses are faecal-oral
- A, E
35
3 hep B antigens + serology tests
- surface antigen (HPsAg): +ve = hep B infection (h/w contained in vaccine)
- E antigen (HBeAg): released during replication (e for escape) = acute hep B infection. increased E antigen = increased infectivity b/c increased replication
- core antigen (HBcAg) = not in blood so will always be negative in blood
36
3 antibodies against hep B
- surface antibody (HBsAb): response to HBsAg (can indicate vaccination or infection)
- E antibody (HBeAb): response to HBeAg (indicates they've previously been through an active infection)
- core antibody (HBcAb): show response to HBcAg. IgM = Middle of an acute infection. IgG = past infection (Gone)
37
how to test for viral load of hep B
- HBV DNA = direct count of viral copies in bloodstream
