Case 12- pathology Flashcards
Diarrhoea
The passage of three or more loose or liquid stools per day with loss of fluid & electrolytes (>500ml per day) from the gastrointestinal tract.
Osmotic diarrhoea
Due to poorly absorbed material in the intestinal lumen, water is attracted and lost in stools
Causes of Osmotic diarrhoea
- Laxatives such as magnesium (Mg2+) salts which are poorly absorbed
- Non-absorbed food, e.g. Sorbitol (artificial sweetener used in sugar-free gum etc)
- Congenital/acquired disorders of digestion, e.g. lactase deficiency and glucose-galactose malabsorption
Secretory diarrhoea
The result of imbalance between secretion & absorption in the intestines. Secretion is stimulated and/or absorption of fluid inhibited.
Causes of secretory diarrhoea
- Ion transporter defects (Cl-/HCO3- exchanger deficiency)
- Enterotoxins, e.g. Escherichia Coli and Cholera
- Laxatives, e.g. dioctyl sodium sulfosuccinate, ricinoleic acid, aloe
- Hormone secreting tumours, e.g. VIP, serotonin
- Many medications can cause a secretory diarrhoea
- Allergy (antigen stimulation)
Diarrhoea- motility disturbance
Increased intestinal motility can mean there is insufficient time for absorption of water, so excess fluid is lost in the stool
Inflammatory diarrhoea
Inflammation of the intestinal mucosa can result in diarrhoea with an osmotic component (because the inflammation causes villous atrophy and reduced absorption of nutrients which remain in the lumen), a secretory component (because inflammatory mediators stimulate fluid secretion), and a motility component (because the increase bulk in the lumen due to the osmotic and secretory components triggers increases peristalsis). Inflammation will also increase the permeability of the mucosa enabling more fluid to enter the intestinal lumen.
Differentiating between osmotic and secretory diarrhoea
You look at the osmotic gap. The osmotic gap is the difference between the measured osmolality of the stool and the osmolality of the stool that is due to the presence of electrolytes. There is a large osmotic gap in osmotic compared to secretory diarrhoea. A gap less then 50 suggests secretory diarrhoea, a gap greater then 100 suggests osmotic diarrhoea. Osmotic diarrhoea will also stop on fasting, because you are no longer consuming the poorly absorbed substance, whereas secretory diarrhoea will usually continue.
Why is the osmotic gap important
This tells us that something other than salt, the major electrolytes (Na+, K+, Cl- and HCO3-) is present in the stool, e.g. sorbitol. Secretory diarrhoea is the result of an imbalance/excessive electrolyte loss so the gap is small.
How to work out faecal electrolyte osmolarity
Faecal electrolyte osmolality is estimated by adding together the osmolality of the two major cations, Na+ and K+ and multiplying that figure by two to account for their associated anions, typically Cl- or HCO3-.
Gastroenteritis
Inflammation of the mucosal lining pf the stomach and intestine
Symptoms of gastroenteritis
Nausea, vomiting, diarrhoea, abdominal cramps with or without fever. Symptoms tend to last between 24-72 hours.
Two main causes of gastroenteritis in adults
Norovirus and bacterial food poisoning
Risk factors for gastroenteritis
Unhygienic living conditions, Socioeconomic factors, Poor sanitation, Immunocompromised, unclean/contaminated water, food contamination/hygiene, travel.
Viral gastroenteritis
More common and severe in children. Short incubation of 4-48 hours. Symptoms are short lasting and self-limiting. Dehydration can cause mortality especially in developing countries.
Transmission of viral gastroenteritis
Faecal-oral transmission, including via surfaces and fomites. Virus presents in high concentrations in stool and vomit. Virus’s can be aerosolised during severe vomiting and diarrhoea. Infective for 2 days after symptoms resolve.
Fomites
An inanimate object capable of carrying infectious agents (bacteria, viruses and parasites) and passively enabling their transmission between hosts i.e. door handles
Astrovirus
Affects mainly children
Adeno group F
Affects both adults and children, tends to be longer lasting then other viral causes, up to 7 days
Sappovirus
Affects both adults and children, similar to norovirus. Diarrhoea more prominent then vomiting (opposite to norovirus)
Rotavirus
Highly infectious, spreads via faecal-oral route. You get watery diarrhoea and vomiting, fever and abdominal pain. Lasts 4-8 days.
Types of Rotavirus
Six serological groups have been identifies, three of which (A,B,C) infect humans
• Group A (90% of infections)- leading cause of diarrhoea among infants and children.
• Group B epidemics of severe diarrhoea in China
• Group C-rare
Rotavirus epidemiology
Most cases between 0-4. Peaks in winter
Rotavirus prevention
A live vaccine, biologically active but cant cause symptoms. Oral administration of vaccine. The 2 vaccines are Rotarix and Rotateq.
Norovirus
Most common cause of infectious intestinal disease resulting in vomiting and diarrhoea
Norovirus disease
Highly infectious. Can spread through aerosols from vomit. Incubation period of 1-2 days. Lasts 1-2 days. No specific treatment you just have to sit it out and rehydration therapy. Sudden onset. Main symptoms are vomiting and diarrhoea
Where do you get Norovirus
Peaks at winter. Spreads in packed area like hospitals and cruise ships. Outbreaks in hospitals mean people cant visit and extended stays in hospitals.
How is Norovirus spread
Spread through faecal oral route i.e. shaking hands, changing nappies, touching surfaces and looking after the ill.
Spread of bacterial gastroenteritis
Uncooked meat or if you do not properly was surfaces uncooked meat has been on
Coliform bacteria
E.coli, Shigella and Salmonella
Mechanism of action of bacterial gastroenteritis- toxins
Bacteria can secrete toxins in to food
Therefore you become unwell once ingested the toxins through food
Onset from ingestion is 1-2 hours
Bacteria with this mechanism include bacillus cereus, clostridium botulinum, staph aureus
Mechanism of action of bacterial gastroenteritis- growth
Bacteria grow in the gut once ingested
Evade immune responses in the gut
Onset from ingestion is around 24 hours, as bacteria need time to grow
Bacteria with this mechanism include campylobacter, salmonella, listeria, shigella, vibrio cholerae
Staph aureus in bacterial gastroenteritis
Grows in contaminated food and releases enterotoxins
These are superantigens - making you sick by causing a full cytokine storm
Mainly staphylococcal enterotoxins A and B. Staphylococcal Enterotoxin A and B (SEA and SEB) are the major causes of food poisoning as they are heat stable superantigens.
Bacillus cereus in bacterial gastroenteritis
Commonly linked to rice, and food sat out for too long
This bacteria forms heat resistant spores
They germinate in food and grow
Diarrhoeal form of the disease - caused by non-haemolytic enterotoxins
Emetic form - caused by emetic toxins
Compylobacter in bacterial gastroenteritis
Most common cause of infective diarrhoea in the developed world
Causes 280,000 cases of food poisoning annually in the UK
Mainly found in raw meat, untreated water and unpasteurised milk
Bacteria spread from contaminated food to uncontaminated food.
Main species are C. Jejuni and C. Coli
E.coli in bacterial gastroenteritis
6 species associated with it
Normally in the gut of animals and humans, contaminates meat at slaughter
Get exposure to it through contaminated food and water contact with animals
Can be serious in young children and elderly
Enterohaemorrhagic E.coli
Produces a toxin which causes food poisoning
Can be shiga toxin / veryocytotoxin
Causes haemorrhagic colitis in children - presenting with bloody diarrhoea, cramping
Haemorrhagic colitis can lead to haemolytic uraemic syndrome (HUS) or thrombocytopenic purpura (TTP). Antibiotics are avoided as they have been associated with HUS
Salmonella in bacterial gastroenteritis
Bacteria which grows on contaminated eggs/poultry/meat/fruit juice
Symptoms include diarrhoea, fever, vomiting, cramps
Duration is 4-7 days
There are 6 subspecies. The major causes are Salmonella enteritidis and Salmonella typhimurium.
Shigella in bacterial gastroenteritis
Cause of bacillary dysentery i.e. inflammatory disease of the intestine
Death through dehydration
Destroys mucosa of the large intestine causing diarrhoea and bloody stool
69% of episodes, and 61% of deaths involve those under 5
Types of shigella
Sh.flexneri = globally widespread Sh.sonni = most cases in the developing world, self limiting Sh.dysenteriae = deadly outbreaks in the developing world
