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Clinical Micro > Viral GI infections and C. difficile > Flashcards

Viral GI infections and C. difficile Flashcards

1
Q

What warning signs are usually absent for viral GI infections that can help distinguish them from bacterial ones?

A

No high fever, bloody diarrhea, or severe abdominal pain

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2
Q

Which symptom is often most prominent for viral GI infections?

A

vomiting

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3
Q

What is the typical duration of a viral GI infection?

A

usually self limiting and over in 72 hours

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4
Q

What are the #1 and #2 causes of viral GI infections worldwide?

A
  1. rotavirus

2. norovirus

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5
Q

What family of virus does norovirus belong to?

A

Caliciviridae

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6
Q

What kind of genome do the Caliciviridae (norovirus) viruses have? what structure?

A

ssRNA (+) and non-enveloped

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7
Q

What is the clinical presentation for someone with acute gastroenteritis brought on by norovirus?

A

Explosive diarrhea and vomiting

- either both or just one of them

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8
Q

What is the approximate incubation period for Norovirus?

A

24-48 hours

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9
Q

What are 4 clinical criteria to diagnose someone with norovirus?

A
  1. short incubation period (1-2 days)
  2. short illness (1-3 days)
  3. high frequency of vomiting
  4. absence of bacterial pathogens
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10
Q

How infectious is norovirus? what is the infectious dose?

A

highly infectious! 1-10 particles only

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11
Q

what is the mode(s) of transmission for norovirus?

A
  1. fecal oral
  2. fomites
  3. airborne (emesis of vomit)
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12
Q

Once the symptoms of norovirus clear, do patients still shed virus?

A

Yes for a couple weeks or months (immunocompromised)

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13
Q

What types of foods are often contaminated with norovirus?

A

shellfish that filter water and concentrate the virus

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14
Q

How many generogroups and subsequent genotypes are there for norovirus?

A

5 genero groups (GI-GV)

34 genotypes

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15
Q

Which two generogroups of norovirus are the primary cause of human disease

A

GI and GII

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16
Q

What generogroup/strain of norovirus is most often responsible for outbreaks? How often do new strains of it emerge?

A

GII.4

New ones every 2-3 years

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17
Q

Can you culture norovirus?

A

no

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18
Q

How can you test for the presence of norovirus?

A

antigen detection or molecular detection with RT-PCR

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19
Q

What are two different genetic targets for RT-PCR with norovirus and when would you want to use either one?

A

Viral RNA dep. RNA pol is good to determine that you HAVE norovirus because they will all have it

Want to look at sequences in more variable regions in order to differentiate between strains of norovirus

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20
Q

What family of viruses does Rotavirus belong to?

A

Reoviridae family

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21
Q

What is interesting about the structure of rotavirus? (3)

A
  1. 11 dsRNA segments
  2. non-enveloped
  3. 3 capsids: outer, intermediate, and inner capsid
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22
Q

How many rotavirus particles are required for infection?

A

as few as 100

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23
Q

How long after a rotavirus infection can you still detect the virus particles?

A

57 days

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24
Q

What is the mode of transmission for rotavirus?

A
  1. fecal oral route

2. food and water borne

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25
Q

What two lab tests are used to detect rotavirus?

A
  1. Antigen testing

2. RT-PCR

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26
Q

What is the clinical presentation of rotavirus in children?

A
  1. low grade fever
  2. vomiting (2-4 days)
  3. Explosive non-bloody diarrhea thats very frequent
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27
Q

What is often the most dangerous result of a rotavirus infection?

A

Severe dehydration due to repetitive diarrheal episodes

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28
Q

What % of severe gastroenteritis in children is caused by rotavirus?

A

~25-65%

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29
Q

What % of deaths for children under 5 are caused by rotavirus?

A

5%

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30
Q

Why was the RotaShield vaccine taken off the market?

A

Some link to to increase in intussusception of the small intestine

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31
Q

What are the two currently prescribed rotavirus vaccines?

A

Rotarix™ (GlaxoSmithKline Inc.) and RotaTeq® (Merck Canada, Inc.)

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32
Q

How do the Rotarix and RotaTeq vaccines differ? which is better?

A

Rotarix: intravenous and monovalent
RotaTeq: oral and pentavalent
- better one

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33
Q

What kind of genome/structure does enteric adenovirus have?

A

linear dsDNA and non-enveloped

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34
Q

What serogroup of adenovirus causes gastroenteritis? what types?

A

Serogroup F: types 40 and 41

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35
Q

What is the incubation period of enteric adenovirus ?

A

3-10 days

36
Q

What is the duration of illness with enteric adenovirus? is it shorter or longer than rotavirus/norovirus?

A

longer: 6-9 days

37
Q

Who is more likely to get infected with enteric adenoviurs?

A

kids, same as rota

38
Q

What are the symptoms of an enteric adenovirus infection?

A

Diarrhea and or vomiting

39
Q

What is the mode of transmission for enteric adenovirus?

A

fecal oral route

40
Q

How is enteric adenovirus detected in the lab?

A

PCR or antigen testing

41
Q

What is the genome type/structure of Astrovirus?

A

ssRNA (+) and non enveloped

42
Q

What is similar/different between Astrovirus and Rotavirus?

A

Symptoms are similar but less vomiting, nausea, and fever

Less infectious than rotavirus

43
Q

How is Astrovirus spread?

A

fecal-oral route

44
Q

Where do outbreaks/when do infections usually occur for astrovirus

A

Mainly kids get it

outbreaks in daycares etc.

45
Q

How is astrovirus detected?

A

with RT-PCR

46
Q

Which of the Hepatitis viruses are bloodborne? Which are water borne?

A

Hepatitis B, C, and D are bloodborne

Hepatitis A and E are waterborne

47
Q

What kind of genome do HAV and HEV have?

A

ssRNA (+)

48
Q

What type of genome(s) do the bloodborne hepatitis types have?

A

B&D are dsDNA, HCV is ssRNA(+)

49
Q

Which of the Hepatitis types are enveloped? which are non-enveloped?

A

HAV and HEV are non-enveloped

HBV, HDV, and HCV are enveloped

50
Q

Which two types of Hepatitis are there vaccines against?

A

HAV and HBV

51
Q

What family of viruses do HAV and HEV belong to ?

A

Picornaviridae

52
Q

What is the incubation period for Hepatitis A?

A

2-6 weeks

53
Q

Whats the prognosis of an infection with HAV?

A

usually self limiting, no chronic disease

54
Q

What’s the difference between kids and adults in terms of symptom presentation for HAV?

A

Children (90% asymptomatic)

Adults (0.9% asymptomatic)

55
Q

How long to symptoms typically last without treatment?

A

2-6 months

56
Q

What symptoms are common for an HAV infection?

A

Fatigue, nausea and vomiting, abdominal pain
Jaundice (yellow skin and eyes)
Dark amber urine (bilirubin excreted in urine)
- can get liver inflammation

57
Q

Why can you only use PCR early on in disease progression for HAV?

A

Early in disease, HAV excreted in stool – PCR possible

As it progresses, antibodies are made and you won’t find it in the feces anymore
- usually this it the point at which people are presenting with symptoms

58
Q

How is a diagnosis with HAV usually made? what is an important differentiation to make in terms of antibodies?

A

using serology

IgM = acute infection vs. IgG = immunity

59
Q

What is the route of transmission for HAV and HEV?

A

fecal oral route

60
Q

What are the two vaccines available for Hep A and E and how do they differ?

A

Havrix (A only) and Twinrix (A&B)

61
Q

How long does it take post-vaccination to establish protection against Hepatitis? How long does it last?

A

Efficacy 95%, lasts 20 years

Protection in 2-4 weeks

62
Q

Antigen detection (EIA) can be used for all enteric viruses we discussed (excluding Hepatitis) except for…

A

astrovirus

63
Q

What are 4 ways to prevent gastroenteritis?

A
  1. Wash hands
  2. Limit person to person contact
  3. Remove source of infection
  4. Decontamination with bleach of environment
64
Q

What kind of bacteria is C. difficile?

A

An anaerobic, spore-forming, Gram positive rod

65
Q

What is C. difficile the major cause of?

A

Nosocomial infectious diarrhea

66
Q

What are the 6 stages in development of disease from C. difficile?

A
  1. Colonization
  2. Antibiotic exposure
  3. Disruption of intestinal microflora
  4. Proliferation and toxin production
  5. Damage to intestinal epithelium
  6. Diarrhea and other diseases
67
Q

What two genes are required for C. difficile to produce toxin and therefore be virulent?

A

TcdA and TcdB

68
Q

How does C. diff colonize the small intestine?

A
  1. You ingest bacteria and spores
  2. the bacteria die in the stomach but the spores survive and make it to the SI
  3. There they will germinate and attach to the mucosal epithelia
  4. Multiplication
69
Q

What is the #1 cause of increased risk to developing C. difficile?

A

Disruption of normal intestinal microflora by antibiotic use

70
Q

What does the toxin released by C. difficile do to the epithelial cells of the SI? What does it inhibit specifically? What is the result?

A

Binds to unknown receptor and is brought in by endocytosis

Inhibits small GTPases

Leads to cytopathic effect of cell rounding which disrupts tight junctions = fluid secretion = diarrhoea

71
Q

How does the immune response influence the pathogenesis of C. difficile?

A

Increased inflammation due to neutrophil infiltration which leads to:
Intestinal damage
Impaired permeability
Fluid secretion

72
Q

What is a common symptom not always caused BY but often occurs with C. difficile infections?

A

Pseudomembranous colitis

73
Q

What is Pseudomembranous colitis?

A

Build up of cell debris and fibrin forming membranous “blisters” throughout the intestine

74
Q

What is the spectrum of disease for C. difficile associated diseases?

A 
Asymptomatic (colonization)
Antibiotic-associated diarrhea (AAD)
Pseudomembranous colitis (PMC)
Toxic megacolon 
Death
75
Q

What is the new, emerging hypervirulent strain of C. difficile called?

A

NAP-1

- north american pulse field gel type 1

76
Q

What makes NAP-1 hypervirulent?

A

a mutation in the regulator gene for the toxin = upregulation of the toxin

77
Q

What antibiotic is used to treat a non-severe presentation of C. difficile?

A

Metronidazole

78
Q

What antibiotic is used to treat a severe presentation of C. difficile?

A

Oral vancomycin

79
Q

What has been shown to be a more effective treatment than even some antibiotics?

A

Fecal transplant

80
Q

What are two lab techniques that can be used to detect C. difficile?

A
  1. culture on selective media

2. Enzyme immunoassays (EIA)

81
Q

What 3 lab techniques can be used to detect the production of C. difficile toxin (ie. a virulent strain)

A
  1. Enzyme immunoassays
  2. Cell Culture Cytotoxicity neutralization assay (CCCNA)
  3. Nucleic acid amplification tests (NAATs)
82
Q

What media/agar is used to culture C. difficile?

A

Cefoxitin cycloserine fructose agar (CCFA)

83
Q

What smell is associated with C. diff growing in culture

A

Barn yard

84
Q

What “common antigen” is being tested for in an EIA for C. diff?

A

Glutamate dehydrogenase

85
Q

What needs to be done after confirming that the sample does contain C. difficile?

A

Need to do a toxin confirmation test to tell if its the virulent kind

Clinical Micro (28 decks)

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