9. GI Infections Flashcards
What are the GI defences to infection?
Sight, smell, memory Saliva (bacteriostatic secretions) Gastric acid Small intestinal secretions (bile) Colonic mucus Anaerobic environment
What are the benefits of gut microbiome?
Harmful bacteria cannot compete for nutrients
Microbiome produces antimicrobial substances
Helps to develop newborns immune system
Produce certain nutrients (vit K)
How can less gut microbiota affect our health?
Obesity - seems to be less diverse population of bacteria
IBD - less diversity
Microbiome composition affects response to chemotherapy
Microbiome composition affects insulin response to food
What do bacteria in colon produce?
SCFAs - acetate, propionate, butyrate
What is the role of butyrate?
Energy source for colonocytes, helps regulate gut environment
What is the role of acetate?
Involved in cholesterol metabolism
What is the role of propionate?
Helps regulate satiety
What is a faecal microbiota transplant?
Faecal transfer from healthy donors to the sick in order to treat disease
Used to treat pseudomembranous colitis (C.diff)
Via NG tube, upper GI endoscopy, colonoscopy, put into caecum
What are gram negative rods that can cause infections of gut?
Salmonella
Campylobacter
Shigella
Enterotoxigenic E.coli
What is a gram positive bacteria that can cause GI infection?
Clostridium difficile
What are the symptoms of salmonella infection?
Nausea, vomiting, watery diarrhoea, fever, abdominal cramping
How does salmonella affect the body?
-Ingested salmonella enter small intestinal cells by endocytosis
In 5%:
-Salmonella pass through endothelial cells to submucosa, where they are taken up by macrophages
-macrophages carry salmonella to reticuloendothelial system, causing lymphoid hyperplasia and hypertrophy
How is salmonella spread?
Ingesting contaminated food or water
How s campylobacter spread to humans?
Present in chicken GI system, spread via faeco-oral route
What are the symptoms of campylobacter infection?
Fever, abdominal cramping, perfuse diarrhoea (can be bloody)
How long does campylobacter usually last?
Incubation period 1-7 days
Can last days to weeks, generally self limiting
What is the treatment for campylobacter infection?
Fluid/electrolyte replacement
Consider antibiotics if bloody diarrhoea
How is shigella spread?
Spread from infected stools, person to person
Only needs a small dose to cause infection
How does shigella affect the body?
Invades large intestine colonocytes, multiplies in cells and invades neighbouring cells
This kills colonocytes and forms abscesses in the mucosa
Gives bloody diarrhoea with mucus and abdominal cramping
How is enterotoxigenic E.coli spread?
Spread by faecal oral route by contaminated water
Common cause of travellers diarrhoea
How does enterotoxigenic E.coli affect the body?
Adheres to enterocytes, produces enterotoxins
These cause the hypersecretion of chloride ions
Water leaves cells into the gut lumen
Gives watery diarrhoea
Following antibiotic therapy, what happens with C.diff?
Can colonise gut and release toxins Toxins A (enterotoxigenic resulting in excessive secretion and inflammation) and B (cytotoxin)
What are the symptoms of C.diff?
Most asymptomatic
Varying degrees of diarrhoea (rarely bloody)
Abdominal cramping
In a few cases - pseudomembranous colitis, toxic megacolon (surgery)
What is pseudomembranous colitis?
Inflammatory condition
Elevated yellow plaques join to form pseudomembrane
What is the treatment for C.diff?
Remove offending antibiotic
Fluid resuscitation
Metronidazole/vancomycin
What is rotavirus?
Very common cause of gastroenteritis in the under 5’s
Double stranded RNA virus
What are the symptoms of rotavirus?
Vomiting with a fever
Diarrhoea - lasts up to a week
What is the treatment for rotavirus?
Managing dehydration
How does rotavirus affect the body?
Chloride secretion - gradient for Na, then water moves into gut
SGLT1 disruption - reduced movement of Na/glucose into enterocyte, higher osmotic load in gut, water moves into gut
Brush border dysfunction - general malabsorption
What is norovirus?
Most common cause of non-bacterial gastroenteritis in world, affects any age
Only requires small dose
Incubation 1-2 days and symptoms last 1-3 days
What are the symptoms of norovirus?
Vomiting, water diarrhoea, fever
How does norovirus affect the body?
Infects small intestine and damages microvilli
Anion secretion, so movement of water into gut lumen
Vomiting is due to delayed gastric emptying
What is the treatment for norovirus?
Oral rehydration
What are 3 parasitic causes of gastroenteritis?
Cryptosporidium - sporozoan (non-motile)
Giardia lamblia - flagellate
Entamoeba - amoeba
How is cryptosporidium spread?
Transmitted by faecal-oral route but can also survive and spread via bodies of wate (infected by animal faeces)
What is cryptosporidium?
Disease caused by ingestion of oocyst - reproduces inside epithelial cells of distal small intestine
What are the symptoms of cryptosporidium?
Water diarrhoea that is normally self limiting
- malabsorption and chloride secretion
What is the treatment for cryptosporidium?
Fluids
Occasionally anti-parasitic treatment in at risk groups - AIDS
How is giardia spread?
Faecal oral route with water supplies often affected in developing countries
What are the symptoms of giardia?
Most are asymptomatic but symptoms are more common in children
Diarrhoea, abdominal cramping
Common cause of persistent diarrhoea
What are the 2 stages in giardias life cycle?
Cyst is ingested - stomach acid/pancreatic enzymes release parasite from cyst, damages proximal small intestine causing symptoms, villus atrophy occurs
Parasite then goes back into cyst stage in colon
What is the treatment for giardia?
Antibiotics and fluid rehydration therapy
What is common post giardia infection?
Lactase deficiency is common - lactose intolerance
What are the symptoms of entamoeba histolytica?
Most cases are asymptomatic
Diarrhoea, liver abscesses (rare)
How is entamoeba histolytica spread?
Faecal-oral route from contaminated food or water
Who does entamoeba histolytica most commonly affect?
People who have travelled to tropical places that have poor sanitary conditions
People who live in institutions that have poor sanitary conditions
Men who have sex with men
How does entamoeba histolytica affect the body?
Infection follows ingestion of cysts
Excystation occurs in colon where trophozoites invade mucosa
Infection can also spread to live
Can cause bloody diarrhoea and inflammatory changes
What is the treatment for entamoeba histolytica?
Anti-protozoals/metronidazole
Severe colitis/toxic megacolon may require surgery
