Infective Gastro Flashcards
What are the common aetiological causes of travellers diarrhoea?
ETEC, other bac. viruses and protozoa
What diagnotic techniques are commonly used to identify bacteria?
Culture
What are the aetiological agents responsible for dysentery?
Shigella, EIEC and protozoa (Entamoeba histolytica)
What the most common parasitic causes of diarrhoea in the developed world?
Giardia and crytosporidium
What is dysentery characterised by?
Blood, mucus and pus in the stool - more than just severe diarrhoea!
What is the problem with anti-motility agents?
They stop peristalsis which is a defense mechanism for the removal of pathogens.
What type of pathogen is the most common cause of diarrhoea in the developing world?
Bacteria
What diagnostic techniques are most commonly used to identify viruses?
Nucleic acid identification
Antigen detection
(Microscopy)
Why is oral rehydration preferable to intravenous in children?
Doesn’t require a highly skilled paediatrician to insert the needle
How do some mothers in developing countries contribute to gastro malnutrition?
They stop breast feeding as they think the milk might be the cause of the problem.
What type of *E. coli *produce shiga toxin?
EHEC (enterohaemorrhagic E. coli)
EAEC if it acquires a plasmid for it
What does EPEC stand for? What symptoms does it cause?
Enteropathogenic E. coli
Non-specific gastro in children in LDCs
What are the two ways diarrhoea kills people?
Immediate phase due to water and electrolyte imbalance
Delayed: mainly due to malnutrition due to enterocyte damage
What is the limitation with culturing faeces?
Generally only pathogens that are easy to find are looked for…
What happens if more than 4-5L of fluid enters the colon?
The excess is excreted as diarrhoea
What level of invasiveness is EPEC in terms of its diarrhoea causing ability?
Adhesive with brush border damage (destroy microvilli)
What is the function of Tir protein in EPEC infection?
Tir is secreted by the type III secretion sytem into enterocytes cytoplasm where is finds its way to the lumen membrane and acts as a receptor for intimin
How does diarrhoea contribute to malnutrition?
Increased nutrient/energy loss
Reduced energy intake (malabsorption, withholding of food)
Of the 5 variants of pathogenic E. coli that cause GI symptoms, which cause severe disease?
EHEC - bloody diarrhoea
EIEC - dysentery
Shiga toxin is associated with which clinical conditions?
Haemorrhagic colitis
Haemolytic-uremic syndrome
What are three classes of anti-diarrhoeal drugs?
Anti-motility agents
Anti-secretory agents
Binding agents
Why don’t animals infected with EHEC get as sick?
They have shiga toxin receptors that absorb the toxin
How does Salmonella manage to systemically invade?
Remains in macrophages
Of the 5 variants of pathogenic *E. coli *that cause GI symptoms which cause milder disease?
EPEC
EAEC
ETEC
What diagnostic techniques are commonly used to identify parasites?
Microscopy
Antigen detection
(detection of nucleic acids)
What is pathotyping? For what pathogen/s is it important?
Determination of virulence factors
- E. coli*
- Yersinia*
What causes enteric fever?
Salmonella Typhi and S. Paratyphi
What does EAEC stand for? What symptoms does it cause?
Enteroaggregative E. coli
Watery diarrhoea in childrens in LCDs
What is the function of Intimin protein in EPEC infection?
Intimin is an attachment protein EPEC uses to mediate intimate adhesion with enterocytes. It binds to Tir, a receptor also produced by EPEC
T/F Shigella has no animal reservoir
True
For what pathogen is serotyping important?
Salmonella
What are some strategies against traveller’s diarrhoea?
Reduce exposure to infectious agent
Immunisation
(Antimicrobials)
T/F Using antibiotics for cholera infection has no effect
False, it shortens the illness and infectious period
Where is the most fluid absorbed?
Duodenum and jejunum.
What species of Shigella causes the most severe dysentery?
S. dysenteriae
What does ETEC stand for? What symptoms does it cause?
Enterotoxigenic E. coli
Causes watery diarrhoea (in young children and travellers in LDCs)
Apart from cholerae what causes Cholera-like diarrhoea?
ETEC - discovered in soilders
What is haemorrhagic colitis? What causes it?
Blood in the stool (not pus)
EHEC
What percentage of under 5 deaths are due to malnutrition?
33%
How do you treat diarrhoea?
Replace fluids - most important
Reduce fluid loss - less important
How much fluid do we secrete from the GIT each day?
100mL
*Entaemoba histolytica *containing what thing indicates it’s the cause of dysentery?
RBCs
Which diarrhoea causing bacteria invade the submucosa?
Salmonella, Campylobacter
What does seeing trophozoites of *Giardia lamblia *in diarrhoea stool samples indicate?
That *Giardia *isn’t causing the diarrhoea because only the cyst stage is release in stool in normal *Giardia *infection. The presence of trophozoites indicates that there is another cause of diarrhoea that is forcing immature *Giardia *down the GIT prematurely.
What is the principle of binding agents?
Attach a toxin’s receptors to sand so that the toxin is absorbed in the gut
T/F Bacteria is the major cause of diarrhoea in the developed world.
False, viruses are!
What does EIEC stand for? What symptoms does it cause?
Enteroinvasive E. coli
Dysentery, any age, mainly LDCs
*Clostridium difficile *is the major cause of what diarrhoeal syndrome?
Antiboitic-associated colitis
T/F V. Cholerae and Shigellae are both found in the environment
False, only Cholerae is found in the environment
Which of the 5 *E. coli *utilise type III secretion systems?
EPEC and EHEC
Has does glucose increase fluid uptake?
It is co-transported into villus cells with Na creating an osmotic gradient for water to travel down
T/F Type III secretion systems are found in pathogens only
True
What is the pattern of diarrhoea when there is malaborption in the colon?
Frequent events of low volume
The causes of foodborne diarrhoea include…
Staph, Salmonella, Clostridium, Bacillus, Vibrio, Listeria, viruses (eg Norovirus), ciguatoxin
What are 4 virulence factors?
Adhesions factors
Endotoxins
Avoidance of immune responses
Invasive ability
When should antiboitics be used in the treatment of diarrhoea?
Cholera
Systemic spread of infection eg typhoid fever
Immunocompromised patients
Severe shigella infections
Protozoal infections (even if carrier only)
Pseudomembranous colitis if severe
What is the most important ingredient in rehydration salts?
Glucose
How much fluid does the colon usually absorb? What is the maximum it can absorb?
1.4L and 4-5L
Why is the name non-specific gastroenteritis inaccurate?
Because it refers to symptoms of diarrhoea and vomiting only and does not include actual inflammation in the GIT
Which virus’ virion is smaller: Rotavirus, Norovirus or enteric adenovirus?
Norovirus at 30nm
The others are 70nm
T/F bacteria are present in amoebic dysentery
False, the amoebae eat the bacteria
Clostridium is a …
Gram positive rod
Forms endospores
Strictly anaerobic
How many species of dysentery causing *Shigella *are there?
4
