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GI infections Flashcards

1
Q

What are the defences of the GI tract?

A
  • Sight, smell, memory
  • Saliva (bacteriostatic secretions)
  • Gastric acid
  • Small intestinal secretions (bile)
  • Colonic mucus (protection from commensal bacteria)
  • Anaerobic environment
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2
Q

Outline the distribution of the gut microbiome

A
  • Proximal gut is relatively sterile
  • Stomach is microaerophilic
  • 10^11 bacteria in colon (anaerobic environment)
  • More than 20% of faecal mass is bacteria
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3
Q

What are the benefits of the microbiome?

A
  • Harmful bacteria cannot compete for nutrients
  • Microbiome produces antimicrobial substances
  • Helps to develop newborn’s immune system
  • Produce certain nutrients (Vit K)
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4
Q

What substances do the bacteria in the gut produce?

A
  • Butyrate - energy source for colonocytes, helps regulate gut environment
  • Acetate - involved in cholesterol metabolism
  • Propionate - helps regulate satiety
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5
Q

How does gut microbiota link to health?

A
  • Obesity - seems to be less diverse population of bacteria
  • Inflammatory bowel disease
  • Microbiome composition affects response to chemotherapy
  • Microbiome composition affects insulin response to food
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6
Q

How does diet affect microbiota?

A
  • High fibre diets influence composition of microbiota
  • Sweeteners disrupt diversity of gut microbiota
  • Gluten free diet leads to lower number of key species
  • Proton pump inhibitors lead to increased GI infections
  • Probiotics/prebiotics good for microbiota
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7
Q

How are faecal microbiota transplants carried out?

A
  • NG/duodenal tubes (can be done under anaesthetic)
  • Upper GI endoscopy
  • Colonoscopy
  • Transplant can be put in caecum
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8
Q

What do faecal microbiota transplants treat?

A
  • Diarrhoea following C. difficile infection (90% success rate)
  • Could also be used to treat IBD
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9
Q

Where do the faeces for FMT come from?

A
  • 10-25 year olds
  • Have not used antibiotics, laxatives or diet pills in past 3 months
  • Do not have GI disease
  • Completely screened
  • Stool must be centrifuged, filtered and diluted
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10
Q

Which gram negative rods cause infection of the gut?

A
  • Salmonella
  • Campylobacter
  • Shigella
  • Enterotoxigenic E-coli
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11
Q

Which gram positive rods cause infection of the gut?

A
  • Clostridium difficile
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12
Q

What are the symptoms of salmonella infections?

A
  • Nausea
  • Vomiting
  • Diarrhoea (mostly non-bloody)
  • Fever
  • Abdominal cramping
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13
Q

How is salmonella spread?

A
  • Spread by ingesting food and water contaminated by salmonella bacteria
  • Takes 48 hours for symptoms to develop
  • Self-limiting (2-3 days)
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14
Q

How does salmonella infect the gut?

A
  • Gains access to enterocytes by endocytosis
  • Move to sub-mucosa
  • Encounters macrophages
  • Macrophages transfer salmonella to reticuloendothelial system where they multiply inside cells
  • Causes lymphoid hyperplasia
  • Re-enter gut from liver
  • Occurs in 5% of infections
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15
Q

What shape is campylobacter?

A
  • Spiral or ‘S’ shaped
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16
Q

How is campylobacter spread to humans?

A
  • Faeco-oral route
  • Food infection, not food poisoning
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17
Q

How does campylobacter infect humans?

A
  • Micro-aerophilic
  • Needs to multiply within host before symptoms appear
  • Releases a cytotoxin
  • Can last days-weeks
  • Self-limiting
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18
Q

What are the symptoms of campylobacter infection?

A
  • Fever
  • Abdominal cramping
  • Diarrhoea (can be bloody)
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19
Q

How long is the incubation period for campylobacter?

A
  • 1-7 days
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20
Q

How is campylobacter treated?

A
  • Fluid/electrolyte replacement
  • Consider antibiotics if diarrhoea is bloody
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21
Q

What does shigella cause?

A
  • Shigellosis
  • Dysentery commonly affecting young children
  • Doesn’t need a large dose to cause disease
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22
Q

How does shigella spread?

A
  • Spread from infected stools
  • Person-person
  • Spreads rapidly between family members
  • Only small dose needed to cause infection
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23
Q

How does shigella infect people?

A
  • Invades large intestine colonocytes by endocytosis
  • Multiplies
  • Invades neighbouring cells
  • This kills colonocytes
  • Abscesses formed in mucosa
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24
Q

What are the symptoms of shigella?

A
  • Bloody diarrhoea
  • Mucus
  • Abdominal cramping
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25
Q

How long does shigella infection last?

A
  • Usually resolved within a week
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26
Q

How does enterotoxigenic E.coli cause infection?

A
  • Adheres to enterocytes
  • Produces enterotoxins
  • Cause hypersecretion of Cl- ions
  • Na+ follows
  • Water leaves cells into gut lumen
  • Common cause of traveller’s diarrhoea
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27
Q

What is enterotoxigenic E.coli ?

A
  • Commensal of the colon but can also be a pathogen
28
Q

How is enterotoxigenic E.coli spread?

A
  • Faecal oral route
  • By contaminated water
29
Q

Which gram negative bacteria can lead to haemolytic uremic syndrome?

A
  • Shigella
  • Campylobacter
30
Q

Outline the properties of C. difficile

A
  • Gram positive
  • Anaerobic
  • Spore forming
  • Minor component of GI tract
  • Spores are very difficult to remove from a hospital environment
31
Q

How is C. difficile spread?

A
  • Faecal oral route
32
Q

How does C. difficile infect people?

A
  • Following antibiotic therapy, C. difficile can colonise gut
  • Releases toxins
33
Q

Which toxins are released by C. difficile?

A
  • Toxin A - enterotoxin that results in excessive secretion and inflammation
  • Toxin B - cytotoxin that kills colonocytes
34
Q

What are the symptoms of C. difficile?

A
  • Most people are asymptomatic
  • Varying degrees of diarrhoea (rarely bloody)
  • Abdominal cramping
35
Q

What are the potential complications of C. difficile?

A
  • Affects <5% of cases
  • Pseudomembranous colitis
  • Toxic megacolon
36
Q

What is pseudomembranous colitis?

A
  • Inflammatory condition
  • Elevated yellow plaques join to form a pseudomembrane
37
Q

How is C. difficile treated?

A
  • Remove offending antibiotic
  • Fluid resuscitation
  • Metronidazole/vancomycin
  • Probiotics
38
Q

What is rotavirus?

A
  • Very common cause of gastroenteritis in under 5s
  • Double stranded RNA virus
39
Q

How is rotavirus spread?

A
  • Faecal-oral route
  • Very small dose required
  • Immunity lasts into adulthood
40
Q

What are the symptoms of rotavirus?

A
  • Vomiting with fever are first symptoms
  • Diarrhoea follows (lasts up to 1 week)
41
Q

How does rotavirus cause diarrhoea?

A
  • Cl- secretion - more Na+ moves into lumen and water follows
  • SGLT1 disruption - reduced movement of Na+/glucose into enterocyte leads to higher osmotic load in gut
  • Reduced brush border enzyme function causing malabsorption
42
Q

How is rotavirus treated?

A
  • Manage dehydration
43
Q

What is norovirus?

A
  • RNA virus
  • Most common cause of non-bacterial gastroenteritis
  • Can affect any ages
  • Huge number of strains so immunity doesn’t develop
  • Only requires small dose
  • Highly contagious
  • Resistant to cleansing
44
Q

What is the incubation for norovirus?

A
  • 1-2 days
  • Symptoms last 1-3 days
45
Q

How does norovirus infect people?

A
  • Infects small intestine
  • Damages microvilli
  • Brush border enzymes are disrupted
46
Q

What are the symptoms of norovirus infection?

A
  • Vomiting due to delayed gastric emptying
  • Watery diarrhoea due to anion secretion
  • Fever
47
Q

How is norovirus treated?

A
  • Oral rehydration therapy
48
Q

What protozoa can infect the GI tract?

A
  • Cryptosporidium (sporozoan)
  • Giardia lamblia (flagellate)
  • Entamoeba (amoeba)
49
Q

How is Cryptosporidium spread?

A
  • Faecal oral route
  • Spread via bodies of water infected by animal faeces
50
Q

How does Cryptosporidium cause disease?

A
  • Ingestion of oocyst (cyst containing parasite)
  • This reproduces inside epithelial cells of distal small intestine
  • Oocytes are excreted in faeces to continue cycle
51
Q

What are the symptoms of Cryptosporidium infection?

A
  • Watery diarrhoea that is normally self-limiting
  • Due to malabsorption and Cl- secretion
52
Q

How is Cryptosporidium treated?

A
  • Supportive (fluids)
  • Occasionally anti-parasitic treatment for at-risk groups
  • AIDS can produce severe symtpoms
53
Q

How is giardia spread?

A
  • Faecal-oral route
  • Water supplies often affected (in developing countries)
54
Q

What are the symptoms of giardia?

A
  • Most infections are asymptomatic
  • Symptoms are more common in children
  • Diarrhoea
  • Abdominal cramping
  • Lasts up to 6 weeks
  • Common cause of persistent diarrhoea
55
Q

What is the incubation period for giardia?

A
  • 10-14 days
56
Q

Outline the life cycle of giardia

A
  • Occurs in 2 stages
    1. Cyst is ingested
  • Stomach acid/pancreatic enzymes release parasite from cyst which then multiplies in small intestine
  • Damages proximal small intestine and causes symptoms
  • Villous atrophy occurs
    2. Parasite goes back to cyst stage in colon
  • Can then be excreted to repeat cycle
57
Q

How is giardia treated?

A
  • Antibiotics and fluid rehydration therapy
58
Q

What is common post-giardia infection?

A
  • Lactase deficiency
59
Q

What are the symptoms of entamoeba infection?

A
  • 80% of cases are asymptomatic
  • Diarrhoea
  • Liver abscesses (rare)
60
Q

How is entamoeba transmitted?

A
  • Faecal-oral route from contaminated food or water
61
Q

Who does entamoeba affect?

A
  • People who have travelled to tropical places that have poor sanitary conditions
  • People who have lived in institutions that have poor sanitary conditions
  • Men who have sex with men
62
Q

How does entamoeba infect people?

A
  • Infection follows ingestion of cysts
  • Excystation occurs in colon where trophozoites invade mucosa
  • Causes bloody diarrhoea and inflammatory changes
  • Infection can spread to liver (abscesses form)
  • Cysts then pass out with faeces
  • Causes further infection
63
Q

How is entamoeba treated?

A
  • Anti-protozoals/metronidazole
  • Severe colitis/megacolon may require surgery
64
Q

How is traveller’s diarrhoea defined?

A
  • Passing 3 or more loose/watery stools
  • +/- fever, abdominal pain
65
Q

What increases the risk of getting traveller’s diarrhoea?

A
  • Place visited (south and east Asia, central America, west and north Africa)
  • Dietary exposure
  • Less than 6 years old
  • Proton pump inhibitors
  • Blood group O
66
Q

How is traveller’s diarrhoea prevented?

A
  • Good hand hygiene
  • Food and water precautions
67
Q

How is traveller’s diarrhoea treated?

A
  • Mild/moderate is treated with hydration (oral rehydration solutions/safe water) and anti-diarrhoeal agents
  • Severe is treated with IV fluids and antibiotics if appropriate

GI tract (23 decks)

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