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MD3002 - GI Disease/Pathology > Bacterial and Viral Infections of the GI Tract > Flashcards

Bacterial and Viral Infections of the GI Tract Flashcards

1
Q

How can gastrointestinal pathogens cause damage to the GI tract?

A
  • Local inflammation
  • Ulceration/perforation of mucosal epithelium
  • Disruption of normal microbiota
  • Pharmacological action of bacterial toxins
  • Invasion to blood or lymphatics
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2
Q

What is e.cadherin important for?

A

the intergrity of tight junctions

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3
Q

What are the potential consequences of epithelial perforation?

A
  • ruptured/perforated ulcer
  • lining of mucosa is perforated
  • leaking of food and gastric juices to the peritoneal or abdominal cavities (spreading infection)
  • treatment requires surgery
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4
Q
A

top = normal SI villi

bottom = villous atrophy

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5
Q

What bacteria are likely to cause bloody stools?

A

Campylobacter and Shigella

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6
Q

What bacteria are likely to cause watery stools?

A

EPEC and cholera

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7
Q

What are the main bacterial diarrhoeal pathogens?

A

Gram negative

  • Vibrio cholerae
  • Escherichia coli
  • Campylobacter jejuni
  • Salmonella spp.
  • Shigella spp.

Gram positive

  • Listeria monocytogenes
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8
Q

Describe Vibrio cholerae

A
  • Gram negative
  • Comma-shaped rod
  • Flagellated
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9
Q

What is Vibrio cholerae characterised by?

A

epidemics and pandemics

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10
Q

Where does Vibrio cholerae flourish?

A

communities with no clean drinking water/sewage disposal

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11
Q

What type of pathogen is Vibrio cholerae

A

human-only pathogen

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12
Q

What type of antigens is Vibrio cholerae based on?

A
  • O1 - early pandemics
  • Non-O1 - recent outbreaks
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13
Q

What vaccines are avaliable for Vibrio cholerae?

A
  • parenternal vaccine: low protective efficiency
  • Oral vaccine: effective and suitable for travels
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14
Q

Describe the pathogenesis of Vibrio cholerae

A
  • Only infective in large doses
  • Many organisms killed in stomach
  • Colonisation of small intestine involving flagellar motion, mucinase, attachment to specific receptors
  • Production of multicomponent toxin
  • Loss fluid and electrolytes without damage
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15
Q

What is the building blocks of the cholera toxin (CTx) and what is it responsible for?

A
  • Oligomeric complex of 6 protein subunits:
    • 1 copy of A subunit (enzymatic)
    • 5 copies of B subunit (receptor binding)
  • Responsible for the characteristic, watery cholera diarrhoea
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16
Q

What are the consequences of the cholera infection?

A
  • Fluid loss of up to 1 litre/hour
  • Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalaemia
  • Hypovolaemic shock
  • 40-60% mortality
  • <1% mortality if given fluid/electrolytes (ORT)
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17
Q

Dsecribe the bacteria Escherichia coli

A
  • Gram negative
  • Bacillus
  • Member of normal gastrointestinal microbiota
  • Some strains possess virulence factors enabling them to cause disease
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18
Q

What are the 6 main types of E.coli causing GI infections?

A
  • EPEC - Enteropathogenic
  • ETEC - Enterotoxigenic
  • VTEC/STEC - Verocytotocin-producing
  • EHEC - Enterohaemorrhagic
  • EIEC - Enteroinvasive
  • EAEC - enteroaggregative
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19
Q

When is EPEC common?

A

sporadic cases and outbreaks of infection in under 5s

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20
Q

When is ETEC common?

A

“travellers’ diarrhoea” (occurs in 20-50% of travellers)

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21
Q

When is VTEC/EHEC common?

A

sporadic cases and outbreaks of gastroenteritis

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22
Q

When is EIEC common?

A

food-borne infection in areas of poor hygiene (often persistent diarrhoea)

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23
Q

Where is EAEC common?

A

resource-poor cpountries

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24
Q

What is the mode of action of E.coli enterotoxins?

A

LT =. Heat-labile toxin

Sta = heat-stable toxin

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25
Q

Describe Campylobacter jejuni bacteria

A
  • Gram negative
  • Helical bacillus
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26
Q

What is the resovoir for C. jejuni

A

large animal resovoir

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27
Q

What type of diarrhoea does C.jejuni

A

food-associated diarrhoea

Commonest case of diarrhoea in developed world

28
Q

What is the mode of transmission of C.jejuni?

A

Transmission through consumption of raw/undercooked meat, contaminated milk

29
Q

Describe the pathogenesis and histological appearance of C. jejuni

A
  • Mucosal inflammation and fluid secretion
  • Inflammation involves entire mucosa
  • Villous atrophy
  • Necrotic debris in crypts
  • Thickening of basement membrane
30
Q

Describe Salmonella spp.

A
  • gram negative
  • bacilli
  • > 200 serotypes of salmonella spp.
31
Q

What type of diarrhoea does salmonella spp. cause?

A

food-associated diarrhoea

32
Q

What is the mode of transmission of Salmonella spp.

A
  • Transmission through consumption of raw/undercooked meat, contaminated eggs and milk
  • Secondary spread can be human-human
33
Q

What are the most important species of salmonella spp.

A
  • S. typhi
  • S. paratyphi
  • S. enteritidis
34
Q

What is the pathogenesis of salmonella spp.

A
  • Ingestion of large numbers of bacteria
  • Absorption to epithelial cells in terminal section of small intestine
  • Penetration of cells and migration to lamina propria
  • Multiplication in lymphoid follicles inflammatory response mediates release of prostaglandins
  • Stimulation of cyclic AMP
  • Release of fluid and electrolytes causing diarrhoea
35
Q

What can s.thyphi and s.paratyphi cause?

A
  • Cause enteric fevers: typhoid and paratyphoid
  • Systemic infections initiated in gastrointestinal tract
36
Q

Describe the consequences for a patient who gets thyphoid fever

A
  • Patient can excrete S. typhi in faeces for several weeks after recovery
  • 1-3% become chronic carriers, most common in women and the elderly
  • Public health concern
  • It’s a notifiable disease
37
Q

What are the vaccinations avaliable for thyoid?

A
  • Oral; live attenuated
    • Booster after 5 years
  • Parenteral; capsular polysaccharide
    • Booster after 2 years
  • 50-80% effective
  • Recommended for travellers to endemic areas
38
Q

Describe the shigella spp. bacteria

A
  • Bacillus
  • Cause shigellosis (bacillary dysentery)
  • Human-only pathogen
39
Q

What are the 4 species of Shigella spp.?

A
  • S. dysenteriae: most serious
  • S. flexneri: severe disease
  • S. boydii: severe disease
  • S. sonnei: mild infections
40
Q

Describe the pathogenesis of shigella infection

A
  • Attaches to mucosal epithelium of distal ileum and colon
  • Causes inflammation and ulceration
  • Rarely invasive
  • Produces Shiga toxin (STx)
  • Diarrhoea watery initially, later can contain blood and mucus
  • Disease usually self-limiting
41
Q

Describe Listeria monocytogenes

A
  • Coccobacillus
  • Causes listeriosis
  • Food-borne pathogen associated with pâté, soft cheese, unpasteurised milk
  • < 1000 organisms may cause disease
42
Q

What population are at risk of listeria?

A
  • Pregnant women (with possibility of infection of the baby in utero or at birth)
  • Immunosuppressed individuals (e.g. those with AIDS or on cancer/immunosuppressive drugs)
  • The elderly
43
Q

What does listeria usually present as?

A

meningitis

44
Q

What are the 3 main viral diarrhoeal pathogens?

A
  • Rota virus
  • Norovirus
  • Enteric Adenovirus
45
Q

Describe the rotavirus

A
  • “rota” – wheel
  • 11 separate segments of double-stranded RNA
  • Infects many mammals
  • Infection commonest in children <2 years old
  • As few as 10 ingested particles can causes disease
  • Seasonal occurrence (commonest in cooler months)
46
Q

What is the transmission mode of rotavirus?

A

Transmission is faeco-oral, but may also be faecal-respiratory

47
Q

Describe the pathogenesis of rotavirus

A
  • Incubation period of 1-2 days
  • Replication of virus in small intestinal epithelial cells at tips of villi
  • Results in callous atrophy
  • Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes
  • Onset of vomiting, diarrhoea lasting 4-7 days
  • Up to 1010-1011 virus particles/gram faeces released
48
Q

What is the vaccination for rotavirus?

A
  • RotaRix; RotaTeq
    • Oral administration (2-3 doses)
    • First dose at 6-10 weeks of age
    • Live, attenuated virus
49
Q

What is norovirus known as?

A

A.k.a “winter vomiting disease”

Accounts for most non-bacterial outbreaks worldwide

50
Q

What type of pathogen is norovirus?

A

human-only pathogen

51
Q

What is the mode of transmission of norovirus?

A
  • Transmission is faeco-oral, contaminated water/shellfish, fomites
  • <100 virions can establish infection
52
Q

What is the vaccine for the norovirus?

A
  • None yet
  • Still approx. 4-5 years away
  • No vaccine is ever 100% effective
  • Hand washing
53
Q

Describe enteric adenovirus

A
  • Accounts for 10% of community-acquired diarrhoeas in young children
  • No seasonal incidence
  • Asymptomatic infections common
  • Mild, but prolonged diarrhoea
54
Q

What are the other diarrhoeal viruses outside the 3 most common ones?

A

Calicivirus

Coronavirus

Astrovirus

55
Q

Desccribe anti-biotic associated diarrhoea

A
  • Does NOT involve ingestion of pathogen or toxin
  • Can arise from disruption of gut microbiota following antibiotic therapy
56
Q

Give the consequences of some antibiotics on the gut microbiota

A
  • Tetracycline – allows colonisation by Staphylococcus aureus and Candida spp.
  • Clindamycin suppresses gut microbiota and allows Clostridium difficile to multiply
  • C. difficile infection is now associated with resistance to vancomycin
57
Q

Describe the C.difficile infection

A
  • Produces spores for survival
  • Produces an enterotoxin and a cytotoxin
58
Q

Describe Helicobacter pylori

A
  • Gram negative
  • Spiral
  • Flagellated
  • Microaerophilic
  • >80% infected individuals are asymptomatic
59
Q

What diseases is H.pylori associated with?

A
  • Duodenal ulcers
  • Gastric ulcers
  • Gastro-oesophageal reflux disease
  • Non-ulcer dyspepsia
60
Q

What are the key features of H.pylori?

A
  • Acid-inhibiting protein – survival in stomach
  • Urease – neutralisation of acid pH
  • Adhesins – binding to gastric epithelium
  • Cytotoxin – damage to gastric epithelium
  • Flagellum – movement through gastric mucus layer
61
Q

What is the first-line treatment of H.pylori?

A

1 week (7 days) triple therapy

Either:

  • Proton pump inhibitor (PPI), Clarithromycin and Amoxicillin

OR

  • Proton pump inhibitor (PPI), Clarithromycin and Metronidazole
62
Q

What is food poisoning?

A

Syndrome is restricted to diseases caused by toxins elaborated by contaminating bacteria in food before it is consumed

63
Q

Give 3 examples of food poisoning toxins

A
  • Emetic toxins of Bacillus cereus
  • Enterotoxin of staphylococcus aureus
  • Neurotoxin Clostridium botulinum
64
Q

Describe food-associated GI infection of Clostridium perfrigens

A
  • Usually caused by type A strains from animal guts and soil
  • Contamination of raw meat products
  • Spores survives cooking and germination takes place
  • Multiplication in large intestine, production of spores and enterotoxin
  • Damage to intestinal epithelium
  • Diarrhoea
65
Q

What is Oral Rehydration therapy?

A
  • Involves the replacement of fluids and electrolytes lost during diarrheal illness
  • 90-95% of cases of acute, watery diarrhoea can be successfully treated with an oral rehydration solution (ORS)
  • ORS increases the resorption of fluids and salts into the intestinal wall
66
Q

What are the ingredients of ORT?

A
  • Glucose (anhydrous): 13.6g/L
  • Sodium chloride: 2.6g/L
  • Potassium chloride: 1.5g/L
  • Trisodium citrate dihydrate: 2.9g/L
  • In addition, fruit juices, coconut water, and other indigenous solutions can adequately approximate ORS

MD3002 - GI Disease/Pathology (11 decks)

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