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Pathology - Y5 > GI Infections > Flashcards

GI Infections Flashcards

1
Q

What is gastroenteritis?

A

A rapid onset diarrheal illness, lasting less than 2 weeks with diarrhoea (loose and unformed stool) three or more times a day or at least 200 g of stool which is either viral or bacterial in aetiology.

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2
Q

What are reportable GI infections?

A

Campylobacter

Salmonella

Shigella

E.Coli 0157

Listeria

Norovirus

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3
Q

What is the incubation period, duration and cause of Campylobacter?

A

Incubation: 1-10 days

Duration: 2-20

Cause: Poultry

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4
Q

What is the incubation period, duration and cause of E.Coli 0157?

A

Incubation: 1-5 days

Duration: 1-4

Causes: HUS, verotoxin

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5
Q

What is the incubation period and duration of Shigella?

A

Incubation period: 12-96hrs

Duration: 5-7

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6
Q

What is the incubation period and duration of Salmonella (non-typhoidal)?

A

Incubation: 8-48h

Duration: 4-7

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7
Q

What is the incubation period and duration of Vibrio parahaemolyticus?

A

Incubation: 24-72h

Duration: 2-10

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8
Q

What are the mechanisms of disease for GI infections?

A

Secretory diarrhoea - toxin production: Cholera toxins and superantigens

Inflammatory diarrhoea vs enteric fever

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9
Q

How do cholera toxins lead to diarrhoea?

A

cAMP: opens Cl channel at the apical membrane of enterocytes.

Leads to efflux of Cl to lumen; loss of H2O and electrolytes.

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10
Q

How do superantigens lead to diarrhoea?

A

Superantigens bind directly to T-cell receptors and MHC molecules outside the peptide binding site.

This leads to massive cytokine production by CD4 cells ie systemic toxicity and suppression of adaptive response.

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11
Q

What is Staph. Aureus food poisoning?

A

1/3 population chronic carriers, 1/3 transient

Spread by skin lesions on food handlers.

Catalase, coagulase positive Gram positive coccus.

Appears in tetrads, clusters on Gram stain

Yellow colonies on blood agar

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12
Q

What is this?

A

Staph. Aureus on blood agar

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13
Q

What is the pathogenesis of Staph. Aureus food poisoning? What is the treatment of Staph. Aureus food poisoning?

A

Produces enterotoxin, an exotoxin that can act as a superantigen in the GI tract, releasing IL1 and IL2, causing prominent vomiting and watery, non bloody diarrhoea.

Don’t treat, self limited.

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14
Q

What is the pathogenesis of Bacillus cereus food poisoning?

A

Gram positive rod-spores

Heat stable emetic toxin: Not destroyed by reheating.

Heat labile diarrhoeal toxin: Food is not cooked to a high enough temperature.

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15
Q

What is this?

A

Bacillus cereus

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16
Q

What are clinical features of Bacillus cereus food poisoning?

A

Watery non bloody diarrhoea; self limited

Rare cause of bacteremia in vulnerable population

Can cause cerebral abscesses

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17
Q

What is clostridia?

A

Gram Positive Anaerobe

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18
Q

What is Clostridium botulinum food poisoning?

A

Botulism

Source: Canned or vacuum packed food (honey/infants)

Ingestion of preformed toxin (inactivated by cooking)

Blocks Ach release from peripheral nerve synapses

Treatment with antitoxin

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19
Q

What is Clostridium pefringens food poisoning?

A

Source: Reheated food (meat)

Normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)

Incubation 8-16hrs

Watery diarrhoea, cramps,little vomiting lasting 24hrs

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20
Q

What is Clostiridium difficile (Pseudomembranous colitis)?

A

3%, 30% of hospitalised patients

Antibiotic related colitis (any but mainly cephalosporins, cipro and clindamycin).

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21
Q

What is the treatment of C.Diff?

A

Oral vancomycin

Adjunct: IV Metronidazole

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22
Q

What is Listeria monocytogenes food poisoning?

A

Outbreaks of febrile gastroenteritis.

ß haemolytic, aesculin positive with tumbling motility.

Source: Refrigerated food (“cold enhancement”),i.e. unpasteurised dairy, vegetables.

Grows at 4 ºC GI watery diarrhoea, cramps, headache, fever, little vomiting.

Perinatal infection, immunocompromised patients.

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23
Q

What is the treatment for Listeria monocytogenes food poisoning?

A

Ampicillin

24
Q

What is Enterobacteriacae?

A

Facultative anaerobes

Glucose/lactose fermenters (LF)

Oxidase negative

25
Q

What is Escherichia coli?

A

Traveller’s diarrhoea

Source: Food/water contaminated with human faeces.

26
Q

What are features of E.Coli enterotoxins?

A

Heat labile stimulates adenyl cyclase and cAMP

Heat stable stimulates guanylate cyclase

Act on the jejeunum, ileum not on colon

27
Q

What are E.Coli variations?

A

ETEC: Toxigenic, main cause of traveller’s diarrhoea

EPEC: Pathogenic, infantile diarrhoea

EIEC: Invasive, dysentery

EHEC: Haemorrhagic O157:H7

EHEC: Shiga-like verocytotoxin causes HUS

28
Q

What is Salmonellae food poisoning?

A

Non lactose fermenters,

H2S producers,

TSI agar,

XLD agar, selenite F broth

29
Q

What are Salmonellae antigens?

A

Cell wall O (groups A-I)

Flagellar H

Capsular Vi (virulence, antiphagocytic)

30
Q

What are three species of Salmonellae?

A

S. typhi (and paratyphi)

S.enteritidis

S.cholerasuis

31
Q

What is S.enteritidis?

A

Enterocolitis transmitted from poultry, eggs, meat.

Invasion of epi- and sub-epithelial, tissue of small and large bowel.

Bacteraemia infrequent

Self limited non bloody diarrhoea ,usually no treatment

Stool positivity

32
Q

What is S.typhi?

A

Typhoid (enteric) fever.

  • Transmitted only by humans
  • Multiplies in Payer’s patches
  • Spreads ERS
  • Bacteraemia, 3% carriers

Slow onset, fever and constipation, splenomegaly, rose spots, anaemia, leucopaenia, bradycardia, haemorrhage and perforation.

Blood culture: Positive

Treatment: ceftriaxone

33
Q

What is Shigellae food poisoning?

A

Non lactose fermenters, non H2S producers, non motile.

Antigens:

  • Cell wall O antigens
  • Polysaccharide (groups A-D): S.sonnei, S.dysenteriae, S.flexneri (MSM)

The most effective enteric pathogen (low ID 50)

No animal reservoir

No carrier state

34
Q

How does Shigellae cause dysentry?

A

Invading cells of mucosa of distal ileum and colon

Producing enterotoxin (Shiga toxin)

35
Q

How is Shigellae treated?

A

Avoid antibiotics (ciprofloxacin if required)

36
Q

What is Vibrios food poisoning?

A

Curved, comma shaped, late lactose fermenters, oxidase positive.

37
Q

What is Vibrio Cholerae?

A

Transmitted by contamination of water and food from human faeces ( shellfish, oysters, shrimp).

Colonisation of small bowel and secretion of enterotoxin with A and B subunit, causing persistent stimulation of adenylate cyclase.

Causes massive diarrhoea (rice water stool) without inflammatory cells.

Treat the losses.

38
Q

What is Vibrio parahaemolyticus?

A

Ingestion of raw or undercooked seafood (i.e. oysters)

Major cause of diarrhoea in Japan..or when cruising in the Carribean:

Self limited for 3 days

Cholerae: Grows in salty 8.5% NaCl.

39
Q

What is Vibrio vulnificus?

A

Cellulitis in shellfish handlers

Fatal septicaemia with D+V in HIV patients

Treat with doxycycline

40
Q

What is Campylobacter?

A

Curved, comma or S shaped

Microaerophilic

C.jejuni at 42 ºC

Oxidase pos, motile

Self limiting but symptoms can last for weeks (20 days)

Only treat if immunocompromised (macrolide)

41
Q

What is the pathogenesis of Campylobacter?

A

Transmitted via contaminated food and water with animal faeces (poultry, meat,unpast. milk).

Watery, foul smelling diarrhoea, bloody stool, fever and severe abdo pain.

Treat with erythromycin or cipro if in the first 4-5days.

42
Q

What other syndromes is Campylobacter associated with?

A

GBS

Reactive arthritis

Reiter’s

43
Q

What is Yersinia enterocolitica?

A

Non lactose fermenter, prefers 4ºC “cold enrichment”

Transmitted via food contaminated with domestic animal excretion:

  • Enterocolitis
  • Mesenteric adenitis
  • Associated with reactive arthritis, Reiter’s
44
Q

What is Mycobacteria (M.Tuberculosis, M.Avium Intracellulare)?

A

Will appear as Gram variable

Always think of TB

45
Q

What is Entamoeba histolytica?

A

Motile trophozoite in diarrhoea

Non motile cyst in nondiarrhoeal illness

Killed by boiling, removed by water filters

4 nuclei

No animal reservoir

46
Q

What is the pathogenesis of Entamoeba histolytica?

A

Ingestion of cysts leads to trophos in ileum. Colonises cecum, colon leading to “flask shaped” ulcer.

Dysentery, flatulence and tenesmus

Chronic: wt loss,+/- diarrhoea, liver abscess

47
Q

How is Entamoeba histolytica diagnosed?

A

Stool micro (wet mount, iodine and trichrome)

Serology in invasive disease

Treat: metronidazole + paromomycin in luminal disease

48
Q

What is Giardia lamblia?

A

Trophozoite “pear shaped”

2 nuclei, 4 flagellas and a suction disk

Ingestion of cyst from fecally contaminated water and food.

Excystation at duodenum:

  • Tropho attaches
  • No invasion
  • Malabsorption of protein and fat
49
Q

What are the risk factors and clinical features of Giardia lamblia?

A

Travellers, hikers, day care, mental hospitals, MSM.

Foul smelling non-bloody diarrhoea, cramps, flatulence, no fever.

50
Q

What is the diagnosis and treatment of Giardia lamblia?

A

Diagnosis: Stool micro, ELISA, “string test”

Treatment: Metronidazole

51
Q

What is Cryptosporidium parvum?

A

Infects the jejunum

Severe diarrhoea in the immunocomromised

Oocysts seen in stool by modified Kinyoun acid fast stain

Treatment: Reconstitution of immune system

52
Q

What is norovirus?

A

Outbreaks

Low ID (18-1000 viral particles)

Environmental resilience (0-60 ºC)

No long term immunity

GII.4 currently predominant strain

53
Q

What is the pathogenesis of rotavirus?

A

dsRNA “wheel like”

Replicates in mucosa of small intestine

Secretory diarrhoea, no inflammation

Watery diarrhoea caused by stimulation of enteric nervous system

54
Q

What is the epidemiology of rotavirus?

A

By age 6 most children worldwide have antibodies to at least one type.

Exposure to natural infection twice confers lifelong immunity.

Huge economic burden worldwide.

55
Q

What is the pathogenesis of adenoviruses?

A

Types 40, 41 cause non bloody diarrhoea <2yrs of age.

Any type in immunocompromised.

Diagnosis: Stool EM, antigen detection, PCR

56
Q

What are three types of adenoviruses and how are they transmitted?

A
  • Poliovirus
  • Enteroviruses (coxsackie, ECHO)
  • Hepatitis A

Transmitted via faecal-oral route but main presentations from other systems.

Pathology - Y5 (59 decks)

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