Case 12- pathology

Question 1

Diarrhoea

Answer 1

The passage of three or more loose or liquid stools per day with loss of fluid & electrolytes (>500ml per day) from the gastrointestinal tract.

Question 2

Osmotic diarrhoea

Answer 2

Due to poorly absorbed material in the intestinal lumen, water is attracted and lost in stools

Question 3

Causes of Osmotic diarrhoea

Answer 3

• 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

Question 4

Secretory diarrhoea

Answer 4

The result of imbalance between secretion & absorption in the intestines. Secretion is stimulated and/or absorption of fluid inhibited.

Question 5

Causes of secretory diarrhoea

Answer 5

• 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)

Question 6

Diarrhoea- motility disturbance

Answer 6

Increased intestinal motility can mean there is insufficient time for absorption of water, so excess fluid is lost in the stool

Question 7

Inflammatory diarrhoea

Answer 7

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.

Question 8

Differentiating between osmotic and secretory diarrhoea

Answer 8

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.

Question 9

Why is the osmotic gap important

Answer 9

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.

Question 10

How to work out faecal electrolyte osmolarity

Answer 10

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-.

Question 11

Gastroenteritis

Answer 11

Inflammation of the mucosal lining pf the stomach and intestine

Question 12

Symptoms of gastroenteritis

Answer 12

Nausea, vomiting, diarrhoea, abdominal cramps with or without fever. Symptoms tend to last between 24-72 hours.

Question 13

Two main causes of gastroenteritis in adults

Answer 13

Norovirus and bacterial food poisoning

Question 14

Risk factors for gastroenteritis

Answer 14

Unhygienic living conditions, Socioeconomic factors, Poor sanitation, Immunocompromised, unclean/contaminated water, food contamination/hygiene, travel.

Question 15

Viral gastroenteritis

Answer 15

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.

Question 16

Transmission of viral gastroenteritis

Answer 16

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.

Question 17

Fomites

Answer 17

An inanimate object capable of carrying infectious agents (bacteria, viruses and parasites) and passively enabling their transmission between hosts i.e. door handles

Question 18

Astrovirus

Answer 18

Affects mainly children

Question 19

Adeno group F

Answer 19

Affects both adults and children, tends to be longer lasting then other viral causes, up to 7 days

Question 20

Sappovirus

Answer 20

Affects both adults and children, similar to norovirus. Diarrhoea more prominent then vomiting (opposite to norovirus)

Question 21

Rotavirus

Answer 21

Highly infectious, spreads via faecal-oral route. You get watery diarrhoea and vomiting, fever and abdominal pain. Lasts 4-8 days.

Question 22

Types of Rotavirus

Answer 22

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

Question 23

Rotavirus epidemiology

Answer 23

Most cases between 0-4. Peaks in winter

Question 24

Rotavirus prevention

Answer 24

A live vaccine, biologically active but cant cause symptoms. Oral administration of vaccine. The 2 vaccines are Rotarix and Rotateq.

Question 25

Norovirus

Answer 25

Most common cause of infectious intestinal disease resulting in vomiting and diarrhoea

Question 26

Norovirus disease

Answer 26

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

Question 27

Where do you get Norovirus

Answer 27

Peaks at winter. Spreads in packed area like hospitals and cruise ships. Outbreaks in hospitals mean people cant visit and extended stays in hospitals.

Question 28

How is Norovirus spread

Answer 28

Spread through faecal oral route i.e. shaking hands, changing nappies, touching surfaces and looking after the ill.

Question 29

Spread of bacterial gastroenteritis

Answer 29

Uncooked meat or if you do not properly was surfaces uncooked meat has been on

Question 30

Coliform bacteria

Answer 30

E.coli, Shigella and Salmonella

Question 31

Mechanism of action of bacterial gastroenteritis- toxins

Answer 31

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

Question 32

Mechanism of action of bacterial gastroenteritis- growth

Answer 32

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

Question 33

Staph aureus in bacterial gastroenteritis

Answer 33

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.

Question 34

Bacillus cereus in bacterial gastroenteritis

Answer 34

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

Question 35

Compylobacter in bacterial gastroenteritis

Answer 35

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

Question 36

E.coli in bacterial gastroenteritis

Answer 36

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

Question 37

Enterohaemorrhagic E.coli

Answer 37

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

Question 38

Salmonella in bacterial gastroenteritis

Answer 38

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.

Question 39

Shigella in bacterial gastroenteritis

Answer 39

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

Question 40

Types of shigella

Answer 40

Sh.flexneri = globally widespread
Sh.sonni = most cases in the developing world, self limiting
Sh.dysenteriae = deadly outbreaks in the developing world