GI infections Flashcards
What are the defences of the GI tract?
- Sight, smell, memory
- Saliva (bacteriostatic secretions)
- Gastric acid
- Small intestinal secretions (bile)
- Colonic mucus (protection from commensal bacteria)
- Anaerobic environment
Outline the distribution of the gut microbiome
- Proximal gut is relatively sterile
- Stomach is microaerophilic
- 10^11 bacteria in colon (anaerobic environment)
- More than 20% of faecal mass is bacteria
What are the benefits of the microbiome?
- Harmful bacteria cannot compete for nutrients
- Microbiome produces antimicrobial substances
- Helps to develop newborn’s immune system
- Produce certain nutrients (Vit K)
What substances do the bacteria in the gut produce?
- Butyrate - energy source for colonocytes, helps regulate gut environment
- Acetate - involved in cholesterol metabolism
- Propionate - helps regulate satiety
How does gut microbiota link to health?
- 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
How does diet affect microbiota?
- 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
How are faecal microbiota transplants carried out?
- NG/duodenal tubes (can be done under anaesthetic)
- Upper GI endoscopy
- Colonoscopy
- Transplant can be put in caecum
What do faecal microbiota transplants treat?
- Diarrhoea following C. difficile infection (90% success rate)
- Could also be used to treat IBD
Where do the faeces for FMT come from?
- 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
Which gram negative rods cause infection of the gut?
- Salmonella
- Campylobacter
- Shigella
- Enterotoxigenic E-coli
Which gram positive rods cause infection of the gut?
- Clostridium difficile
What are the symptoms of salmonella infections?
- Nausea
- Vomiting
- Diarrhoea (mostly non-bloody)
- Fever
- Abdominal cramping
How is salmonella spread?
- Spread by ingesting food and water contaminated by salmonella bacteria
- Takes 48 hours for symptoms to develop
- Self-limiting (2-3 days)
How does salmonella infect the gut?
- 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
What shape is campylobacter?
- Spiral or ‘S’ shaped
How is campylobacter spread to humans?
- Faeco-oral route
- Food infection, not food poisoning
How does campylobacter infect humans?
- Micro-aerophilic
- Needs to multiply within host before symptoms appear
- Releases a cytotoxin
- Can last days-weeks
- Self-limiting
What are the symptoms of campylobacter infection?
- Fever
- Abdominal cramping
- Diarrhoea (can be bloody)
How long is the incubation period for campylobacter?
- 1-7 days
How is campylobacter treated?
- Fluid/electrolyte replacement
- Consider antibiotics if diarrhoea is bloody
What does shigella cause?
- Shigellosis
- Dysentery commonly affecting young children
- Doesn’t need a large dose to cause disease
How does shigella spread?
- Spread from infected stools
- Person-person
- Spreads rapidly between family members
- Only small dose needed to cause infection
How does shigella infect people?
- Invades large intestine colonocytes by endocytosis
- Multiplies
- Invades neighbouring cells
- This kills colonocytes
- Abscesses formed in mucosa
What are the symptoms of shigella?
- Bloody diarrhoea
- Mucus
- Abdominal cramping
How long does shigella infection last?
- Usually resolved within a week
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
What is enterotoxigenic E.coli ?
- Commensal of the colon but can also be a pathogen
How is enterotoxigenic E.coli spread?
- Faecal oral route
- By contaminated water
Which gram negative bacteria can lead to haemolytic uremic syndrome?
- Shigella
- Campylobacter
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
How is C. difficile spread?
- Faecal oral route
How does C. difficile infect people?
- Following antibiotic therapy, C. difficile can colonise gut
- Releases toxins
Which toxins are released by C. difficile?
- Toxin A - enterotoxin that results in excessive secretion and inflammation
- Toxin B - cytotoxin that kills colonocytes
What are the symptoms of C. difficile?
- Most people are asymptomatic
- Varying degrees of diarrhoea (rarely bloody)
- Abdominal cramping
What are the potential complications of C. difficile?
- Affects <5% of cases
- Pseudomembranous colitis
- Toxic megacolon
What is pseudomembranous colitis?
- Inflammatory condition
- Elevated yellow plaques join to form a pseudomembrane
How is C. difficile treated?
- Remove offending antibiotic
- Fluid resuscitation
- Metronidazole/vancomycin
- Probiotics
What is rotavirus?
- Very common cause of gastroenteritis in under 5s
- Double stranded RNA virus
How is rotavirus spread?
- Faecal-oral route
- Very small dose required
- Immunity lasts into adulthood
What are the symptoms of rotavirus?
- Vomiting with fever are first symptoms
- Diarrhoea follows (lasts up to 1 week)
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
How is rotavirus treated?
- Manage dehydration
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
What is the incubation for norovirus?
- 1-2 days
- Symptoms last 1-3 days
How does norovirus infect people?
- Infects small intestine
- Damages microvilli
- Brush border enzymes are disrupted
What are the symptoms of norovirus infection?
- Vomiting due to delayed gastric emptying
- Watery diarrhoea due to anion secretion
- Fever
How is norovirus treated?
- Oral rehydration therapy
What protozoa can infect the GI tract?
- Cryptosporidium (sporozoan)
- Giardia lamblia (flagellate)
- Entamoeba (amoeba)
How is Cryptosporidium spread?
- Faecal oral route
- Spread via bodies of water infected by animal faeces
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
What are the symptoms of Cryptosporidium infection?
- Watery diarrhoea that is normally self-limiting
- Due to malabsorption and Cl- secretion
How is Cryptosporidium treated?
- Supportive (fluids)
- Occasionally anti-parasitic treatment for at-risk groups
- AIDS can produce severe symtpoms
How is giardia spread?
- Faecal-oral route
- Water supplies often affected (in developing countries)
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
What is the incubation period for giardia?
- 10-14 days
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
How is giardia treated?
- Antibiotics and fluid rehydration therapy
What is common post-giardia infection?
- Lactase deficiency
What are the symptoms of entamoeba infection?
- 80% of cases are asymptomatic
- Diarrhoea
- Liver abscesses (rare)
How is entamoeba transmitted?
- Faecal-oral route from contaminated food or water
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
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
How is entamoeba treated?
- Anti-protozoals/metronidazole
- Severe colitis/megacolon may require surgery
How is traveller’s diarrhoea defined?
- Passing 3 or more loose/watery stools
- +/- fever, abdominal pain
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
How is traveller’s diarrhoea prevented?
- Good hand hygiene
- Food and water precautions
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
