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MBCHB3: Blood, Immunity and Infection > Lecture 23: Diarrhoea and acute GI illness > Flashcards

Lecture 23: Diarrhoea and acute GI illness Flashcards

1
Q

Define gastroenteritis, diarrhoea and acute, persistent & chronic:

A

Gasteroenteritis: Sydnrome diarrhoea and/or vomiting

Diarrhoea: 3+ loose stools in 24 hrs

Acute: <14 days
Persistent: 14-30 days
Chronic: >30 days

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2
Q

Write some brief notes on anatomy and function of GI tract:

A

Fluid and nutrient absorption!

  • Villi + Microvilli
  • Crypts
  • Mucous layer
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3
Q

Describe the innate immunity features of the GI tract:

A
  • Intestinal motility -> Helps clear bacteria out (loperamide stops gut motility)
  • Intestinal microflora
  • Gastric acidity (Norovirus and guradia are resistant tho)
  • Changes in Na/glucose/fat absorption can result in loose stools / osmotic diarrhoea (think toxins)
  • M Cells aid dendritic cells sampling in payers patches continuously
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4
Q

Describe the role of the human microbiome in GI health:

7 features

A
  1. Protects against pathogens
  2. Synthesis of vitamins
  3. Immune system development
  4. Promotion of intestinal angiogenesis
  5. Promotion of fat storage
  6. SCFA production by fermentation of dietary fibre
  7. Modulation of central nervous system
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5
Q

Give an overview of the mechanisms of infectious diarrhoea:

A
  • Essentially an altered movement of ions and water (Water following the osmotic gradient)
  • Enteric pathogens alter the balance towards net secretion -> Diarrhoea
  • Occurs either through:

Direct modulation of ion process and function (Non-inflammatory diarrhoea)

Indirectly through inflammation, neuropeptides or loss of absorptive surface (Inflammatory diarrhoea)

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6
Q

What is distinct about non-inflammatory diarrhoea and what causes it?

A
  • Watery diarrhoea WITHOUT blood or pus.
  • Mucosal disruption affecting absorption/secretory processess without causing acute inflammation or mucosal destruction

Causes include:

  • Enterotoxin ingestion
  • Enterotoxin producing organisms
  • Viruses that adhere to mucosa
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7
Q

Describe the mechanisms of inflammatory diarrhoea:

A
  • Predominantly target large bowl (Esp. distal ileum and colon)
  • Acute mucosal inflammation with various degrees of mucosal ulceration
  • Blood, mucus and WCC in stool, pain and fever

Causes include:

  • Secretions of cytotoxins
  • Invasion of intestinal epithelium causing acute inflammatory reaction (Shigella, Campylobacter, salmonella)
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8
Q

What are the diagnostics for diarrhoea?

A

Trying to identify a pathogen within normal flora (Vs sterile i.e CSF)

  • Microscopy
  • Culture
  • Antigen testing
  • Molecular (PCR/multiplex PCR)
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9
Q

Write some notes on using culture for diagnosis:

A
  • Stool: Non-sterile, dont want to grow non-pathogenic bacterial (selective media)
  • Need to grow pathogenic bacteria that may be present in small numbers relative to other bacteria
  • Need to be able to differentiate pathogenic bacteria from non-pathogenic bacteria easily.
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10
Q

Whats the function of chromogenic agar?

A
  • Target specific pathogenic species based on enzyme activity
  • Generally target organism grow as coloured colonies due to metabolism of one or more chromogenic enzyme substrates
  • Reduces the number of colonies that require further identification
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11
Q

Write some notes on syndromic panel molecular testing:

A
  • Utilise multiplex PCR testing to perform molecular testing for variety of viral/bacterial/parasitic pathogens
  • Single sample, single test - multiple different pathogens
  • Rapid and easy to use
  • Only detect what primers bind to
  • No organism for susceptibility testing (Individual and public health implications)
  • Can be difficult to interpret (Detecting DNA not viable organism, remain positive after resolution/treatment) i.e rotavirus post vaccine
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12
Q

Whats the general management of diarrhoea?

A
  • Symptomatic relief
  • Rehydration
  • Prevent transmission
  • Identify those at risk of severe disease which requires treatment i.e those with severe/prolonged diarrhea, invasive disease or risk factors for complications
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13
Q

What aspects of history are you looking for in a patient with diarrhea?

A
  • Assessment of dehydration (Oral vs IV)
  • Co-morbidities and risk factors for severe disease
  • Transmission and public health risk (impact on work)
  • Specific treatment
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14
Q

What are some examples of diarrhea and their causes?

A

Non-inflammatory / small bowel infection

  • > Food poisoning
  • > Viral gastroenteritis

Inflammatory diarrhea / colitis

  • > Campylobacter
  • > Shigella
  • > Salmonella

Giardia (Parasite)
Metronidazole

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15
Q

Write some notes on food poisoning: and an example:

A
  • Acute vomiting (Some forms have diarrhea also)
  • Toxin ingestion (Bacteria multiply outside host, toxins consumed)

Staphylococci Spp or B cereus

  • Multiply at range of temps.
  • Often reproduce in food that is left to cool slowly at room temp

Rapid onset but resolves quickly

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16
Q

What are the five major causes of small bowel / viral gastroenteritis

A

Five major causes

  • Rotavirus
  • Norovirus
  • Enteric adenovirus

Sapovirus and astrovirus (significance unclear)

17
Q

Whats the pathogenesis of small bowel / viral gastroenteritis:

A
  • Infection of small intestine, enterocyte epithelium
  • > Adherence of mucosa and disruption of absorption/secretory processes WITHOUT acute inflammation or mucosal destruction
  • > Viral replication leading to epithelial cells becoming necrotic - loss of enzymes that break down CHO and proteins -> Primary malabsorption
  • Localized responses causing ischemia of villi and villous atrophy -> reduced absorptive capacity
  • Autonomic dysfunction (i.e vomiting), increased motility of small intestine
18
Q

How does norovirus cause disease?

A
  • 1/5th of all gastro
  • Transmission is feacal-oral, human-human or environmental
  • Short incubation
  • Low infectious dose = spreads rapidly
  • Delayed gastric emptying common therefore vomiting a feature

= Strict hand hygiene
= Doesnt culture therefore PCR needed

19
Q

Write some notes on rotavirus:

A
  • Mostly children
  • Severe disease in 3 months to two years
  • Fever and vomiting followed by diarrhoea
  • Now have oral vaccine 6 weeks and 3 months.
20
Q

What sort of diarrhoea does shigella cause?

A

Inflammatory diarrhoea

21
Q

How is shigella transmitted and describe its pathogenesis:

A
  • Feacal oral and sexual transmission
  • Can withstand low pH and low infectious dose.
  • Invasion of large intestine mucosa causing ulceration and inflammation however usually only superficial not penetrating beyond lamina propria
  • Incubation 1-4 days, shed for weeks after illness
22
Q

Describe shigella presentation and treatment:

A

Presentation:
- Watery diarrhoea with fever and abdo pain followed diarrhoea with blood, mucus and pus.

Treatment

  • Antimicrobials useful for reducing shedding
  • Usually self limiting but antibiotics shorten duration, transmission and severity
  • Widespread and increasing antibiotic resistance
23
Q

Describe the spread of campylobacter jejuni:

A

Feacal oral spread predominantly through contaminated food/water or contact with animals although human-human sprad can occur

Susceptible to gastric acid, drying, freezing, pasteurization or chlorination

24
Q

Describe how campylobacter jejuni causes disease:

A
  • Causes inflammatory colitis of D,J,I
  • Bacteria enter intestinal epithelium through M-cells and spread to adjacent cells -> Local inflammatory response and toxin induced cell damage -> Inflammatory diarrhoea
25
Q

Describe the treatment of campylobacter jejuni:

A
  • Generally self limiting
  • Antibiotics reduce duration of symptoms by <2 days and do eradicate stool carriage. Person-person spread is rare
  • Use antibiotics in those with severe or prolonged symptoms, high risk complications or high risk transmission
26
Q

Write some notes on salmonella pathogenesis:

A
  • Disease in ilium and to a lesser extent colon
  • Low infectious dose, long and variable incubation period.
  • Person-person spread or via contaminated food and water
27
Q

Describe salmonella resistance to antibiotics

A
  • Intrinsically resistant to first and second gen cephalosporins and aminoglycosides
  • Increasing resistant due to plasmids
28
Q

What are the two syndromes seen with salmonella:

A
  • Typhoid salmonella generally presenting with high fever and headache typically without diarrhoea, with bacteremia; require antibiotic treatment
  • Non-typhoidal salmonella causing intestinal infection presenting with fever and diarrhoea and occasionally extraintestinal infections including bacteraemia, osteomyelitis and endovascular infection
29
Q

Describe treatment for salmonella:

A

Adults - Antibiotics unnecessary and may prolong excretion

  • Consider in those with severe disease, immunocompromised, or with prosthetic vascular grafts
  • Infants <3months usually require treatment
30
Q

How can giardia be transmitted?

A
  • Feacal oral via ingestion of cysts in contaminated food or water
  • Low infectious doses
31
Q

Describe giardia:

A

Non invasive: Trophozoites (Active form) adhere to the epithelium of upper small intestine and damage mucosal brush border without invasion

32
Q

How doe giardia cause disase?

A

Loos of brush border -> Loss of absorptive surface and diffuse shortening of villi

Often slow onset can be present for months and cause acute/chronic diarrhoea, abdo pain and malabsorption

33
Q

How is giardia diagnosed and treated?

A
  • Diagnosis via stool examination for cysts/trophozoites and increasingly antigen detection or PCR
  • Treatment with metronidazole
34
Q

Write some notes on the function of metronidazole:

A
  • Inert - antimicrobial activity depends on activation after entering the organisms cell via passive diffusion (Aerobic bacteria cant activate prodrugs, thus inefective)
  • Activated drugs inhibits DNA synthesis and induces DNA damage -> DNA degradation and cell death
  • Near 100% bioavail
  • LOw protein binding = large VoD
  • Well tolerated, peripheral neuropathy with prolonged use tho
  • If alcohol also used then can cause nausea, diarrhoea etc
35
Q

Describe the differential approach to diarrhoea:

A
  • Intra-abdo infection or systemic infection
  • Non-infectious causes of diarrhoea
  • > Inflammatory bowel disease
  • > Coeliac disease
  • > Meds
  • > IBS

MBCHB3: Blood, Immunity and Infection (41 decks)

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