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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
How long does shigella infection last?
- Usually resolved within a week
26
How does enterotoxigenic E.coli cause infection?
- Adheres to enterocytes - Produces enterotoxins - Cause hypersecretion of Cl- ions - Na+ follows - Water leaves cells into gut lumen - Common cause of traveller's diarrhoea
27
What is enterotoxigenic E.coli ?
- Commensal of the colon but can also be a pathogen
28
How is enterotoxigenic E.coli spread?
- Faecal oral route - By contaminated water
29
Which gram negative bacteria can lead to haemolytic uremic syndrome?
- Shigella - Campylobacter
30
Outline the properties of C. difficile
- Gram positive - Anaerobic - Spore forming - Minor component of GI tract - Spores are very difficult to remove from a hospital environment
31
How is C. difficile spread?
- Faecal oral route
32
How does C. difficile infect people?
- Following antibiotic therapy, C. difficile can colonise gut - Releases toxins
33
Which toxins are released by C. difficile?
- Toxin A - enterotoxin that results in excessive secretion and inflammation - Toxin B - cytotoxin that kills colonocytes
34
What are the symptoms of C. difficile?
- Most people are asymptomatic - Varying degrees of diarrhoea (rarely bloody) - Abdominal cramping
35
What are the potential complications of C. difficile?
- Affects <5% of cases - Pseudomembranous colitis - Toxic megacolon
36
What is pseudomembranous colitis?
- Inflammatory condition - Elevated yellow plaques join to form a pseudomembrane
37
How is C. difficile treated?
- Remove offending antibiotic - Fluid resuscitation - Metronidazole/vancomycin - Probiotics
38
What is rotavirus?
- Very common cause of gastroenteritis in under 5s - Double stranded RNA virus
39
How is rotavirus spread?
- Faecal-oral route - Very small dose required - Immunity lasts into adulthood
40
What are the symptoms of rotavirus?
- Vomiting with fever are first symptoms - Diarrhoea follows (lasts up to 1 week)
41
How does rotavirus cause diarrhoea?
- 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
How is rotavirus treated?
- Manage dehydration
43
What is norovirus?
- 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
What is the incubation for norovirus?
- 1-2 days - Symptoms last 1-3 days
45
How does norovirus infect people?
- Infects small intestine - Damages microvilli - Brush border enzymes are disrupted
46
What are the symptoms of norovirus infection?
- Vomiting due to delayed gastric emptying - Watery diarrhoea due to anion secretion - Fever
47
How is norovirus treated?
- Oral rehydration therapy
48
What protozoa can infect the GI tract?
- Cryptosporidium (sporozoan) - Giardia lamblia (flagellate) - Entamoeba (amoeba)
49
How is Cryptosporidium spread?
- Faecal oral route - Spread via bodies of water infected by animal faeces
50
How does Cryptosporidium cause disease?
- Ingestion of oocyst (cyst containing parasite) - This reproduces inside epithelial cells of distal small intestine - Oocytes are excreted in faeces to continue cycle
51
What are the symptoms of Cryptosporidium infection?
- Watery diarrhoea that is normally self-limiting - Due to malabsorption and Cl- secretion
52
How is Cryptosporidium treated?
- Supportive (fluids) - Occasionally anti-parasitic treatment for at-risk groups - AIDS can produce severe symtpoms
53
How is giardia spread?
- Faecal-oral route - Water supplies often affected (in developing countries)
54
What are the symptoms of giardia?
- Most infections are asymptomatic - Symptoms are more common in children - Diarrhoea - Abdominal cramping - Lasts up to 6 weeks - Common cause of persistent diarrhoea
55
What is the incubation period for giardia?
- 10-14 days
56
Outline the life cycle of giardia
- 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
How is giardia treated?
- Antibiotics and fluid rehydration therapy
58
What is common post-giardia infection?
- Lactase deficiency
59
What are the symptoms of entamoeba infection?
- 80% of cases are asymptomatic - Diarrhoea - Liver abscesses (rare)
60
How is entamoeba transmitted?
- Faecal-oral route from contaminated food or water
61
Who does entamoeba affect?
- 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
How does entamoeba infect people?
- 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
How is entamoeba treated?
- Anti-protozoals/metronidazole - Severe colitis/megacolon may require surgery
64
How is traveller's diarrhoea defined?
- Passing 3 or more loose/watery stools - +/- fever, abdominal pain
65
What increases the risk of getting traveller's diarrhoea?
- 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
How is traveller's diarrhoea prevented?
- Good hand hygiene - Food and water precautions
67
How is traveller's diarrhoea treated?
- 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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