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Microbiology Exam 2 > GI viruses > Flashcards

GI viruses Flashcards

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1
Q

In select populations, severe gastroenteritis can lead to hospitalization. Name these populations.

A

-very young, elderly, immunocompromised

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2
Q

Acute infectious gastroenteritis (AIG) is especially a concern in which environment?

A
  • hospitals

- especially viruses

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3
Q

AIG accounts for ______ of deaths among children < 5 y.o. worldwide.

A
  • 15%

- one of the leading causes of early childhood death in resource-poor countries

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4
Q

Describe the common infectious causes of AIG between developed and developing countries.

A
  • developed: mainly due to viruses

- developing: mainly due to parasites and bacteria**

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5
Q

For AIG, diarrhea is always a symptom. T/F.

A
  • False; variety of signs and symptoms

- diarrhea, vomiting, fever, cramps, irritability, headache, anorexia, malaise, etc…

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6
Q

Differential diagnosis of AIG is broad. List some epidemiological clues that can help.

A
  • time of year
  • age of patient
  • travel history
  • careful exposure history
  • vaccination history
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7
Q

Enteric pathogens are classically divided into 3 categories based on how they effect host GI physiology. Name these 3 categories.

A
  1. minimally invasive or enterotoxin-secreting causing watery diarrhea
  2. Inflammatory or cytotoxic destruction of mucosa of small bowel or collow leading to diarrhea with leukocytes and blood in stool
  3. penetrate through intact mucosa and access reticuloendothelial system leading to systemic illness (enteric fever syndrome)
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8
Q

Viral GE is caused by many viruses and all present with a similar disease or suddent onset and short duration (1-10 days). Describe the stools.

A
  • water stools without mucous or blood
  • fecal leukocytes absent of minimal
  • often called stomach flu
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9
Q

Viral GE is self-limited in healthy, well-nourished persons with normal immune systems. But what 3 characteristics are seen in the immunocompromised?

A
  1. chronic diarrhea
  2. increased mortality
  3. prolonged fecal shedding
    * *also serious illness in those unable to rehydrate**
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10
Q

List the 5 viruses covered, their families, and their genomes, if they are enveloped or not.

A
  1. Rotavirus; reoviridae; segments dsRNA
  2. Adenovirus; adenoviridae; linear ds DNA
  3. Norovirus; caliciviridae; +ssRNA
  4. Sapovirus; caliciviridae; +ssRNA
  5. Astrovirus; astroviridae; +ssRNA

*ALL NON-ENVELOPED Fecal oral is possibility!!

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11
Q

When does viral GE hit? What age is its peak incidence?

A
  • 70% of admissions occur in winter
  • viruses account for 50-90% of acute GE requiring hospitalization
  • peak incidence in 6-24 months, but can affect all ages and classes worldwide
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12
Q

List the 5 viruses discusses, their peak age of incidence, and when they occur.

A
  1. Rotavirus; 6 months-2 yr. old; Winter in temperate places or year round in tropical
  2. Adenovirus; infants and young children; year round-epidemics
  3. Norovirus; children AND adults; winter peak with year round occurrence
  4. Sapovirus; children (infants and toddlers) mainly and adults; year round
  5. Astrovirus; mainly young children; year round
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13
Q

With the exception of ________, the incubation period is very short for most of these viruses. Vomiting and diarrhea usually lasts for several days or more, with prolonged diarrhea being observed for the ____________ vomiting and diarrhea being of very short duration for _________. Shedding of the virus in stools in affected individual last for 8-10 days for most viruses, with what exception?

A
  • adenovirus
  • adenovirus (12 days) and noro (4-6)
  • norovirus
  • norovirus
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14
Q

Transmission of viruses causing gastroenteritis

A
  • fecal oral route from person to person
  • contaminated fomites
  • contaminated food or water
  • possible respiratory secretions
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15
Q

Heathcare-associated spread is common with viral GE, particularly for which ones?

A
  • rotavirus

- norovirus

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16
Q

What is viral GE transmission so efficient? What is an efficient way to kill these viruses?

A
  • physical hardiness of GI viruses due to no envelope
  • high virus concentration in stools
  • highly contagious; will only 10-20 particles needed for infection
  • resistant to inactivation by various standard cleaning solutions
  • can be inactivated by antiseptic agents that have high concentrations (>40%) of alcohols and by bleach
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17
Q

Pathological changes associated with Viral GE

A
  • usually patchy with intervening areas of apparently normal mucosa
  • shortening of villi, exfoliation, elongation of crypts, increase in mononuclear cells in lamina propria
  • virus multiplies in enterocytes at tips of villi
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18
Q

What has been the leading cause of severe dehydrating diarrhea necessitating hospitalization in infants and young children worldwide?

A

-rotavirus

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19
Q

Describe the structure of rotavirus

A
  • family reoviridae (respiratory enteric orphan)
  • naked
  • triple-layered icosahedral capsid
  • double stranded segmented RNA
  • particles resemble wheels
20
Q

Rotavirus is composed of 11 RNA segments. What do they encode?

A
  • 6 structural proteins (VP1-VP4, VP6, VP7)

- 6 nonstructural proteins (NSP1-6) involved in genome replication

21
Q

How are rotaviruses seriologically classified?

A

-classified into 7 serogroups (A-G) based on VP6 properties

22
Q

Severe GE caused by rotavirus commonly affects what age group?

A

-infants and children 6 months-2 years old

23
Q

Marked seasonality to rotavirus in temperate climates with what conditions promoting spread? Where will outbreaks occur?

A
  • cool, dry weather

- readily spread in day-care centers, neonatal units, and families

24
Q

Why does rotavirus not infect infants right after birth?

A

-infants less than 3 months old are protected by passive maternal antibody

25
Q

Clinical symptoms of rotavirus

A
  • fever, explosive, watery diarrhea and vomiting (up to 40 times/day)
  • rapidly dehydrating
  • systemic spread with viremia and spread to extraintestinal tissues has been documented, particularly in immunocompromised children
26
Q

Describe the Rotavirus vaccines; how do they work?

A
  • RotaTeq: live, oral
  • Rotarix: live, oral
  • must induce mucosal immune response to be protective, intestinal antibodies (but not serum antibodies) correlate with protection; IgA
  • herd immunity is possible
27
Q

Effects of Rotavirus vaccine

A
  • 2-4 month delay in onset

- 50% reduced magnitude in incidence

28
Q

Describe the calciviridae family; why they have the name, and which human genera infect humans.

A
  • genetically diverse group of small, round viruses
  • naked
    • ssRNA
  • Norovirus and Sapovirus infect humans
  • cup-like indentations on surface
29
Q

Compare Noroviruses to Sapoviruses in affected age groups, clinical symptoms, outbreak potential, and modes of transmission

A
  • Noro: all ages; vomiting and diarrhea; high outbreak potential; fecal oral, contaminated food, water, or fomites, droplets from vomit
  • Sapo: mainly children; mild GE with less vomiting; low outbreak potential; fecal oral, direct person to person spread
30
Q

What is currently considered to be the most widely recognized agents of infectious GE in adults and older children in both developed and developing countries?

A
  • Noroviruses

- leading cause of GE in adults, second leading cause of severe diarrheal disease in young children

31
Q

Norovirus clinical Syndrome and differences in age

A
  • 1-2 day incubation and 1-3 day illness
  • Prominent features: nausea, vomiting, nonblood diarrhea, abdominal cramps
  • children vomit; adults get diarrhea
  • shedding may last for more than 3 weeks, especially with chronic diarrhea in immunocompromised
32
Q

If you had to guess what caused an outbreak of viral GE what would you guess?

A
  • Norovirus

- common source that occurs year round with peak in winter

33
Q

Major places of Norovirus outbreaks

A
  • defined populations and diverse settings

- nursing homes, schools, cruise ships**, restaurants

34
Q

One of the reasons Norovirus is so key in outbreaks, is its high rate of transmission. Give the 4 ways with examples of how it is transmitted.

A
  • Food: shellfish, salad, frosting, celery, cakes; things that need handling and no subsequent cooking
  • Water: groundwater supplies, community water systems, pools, lakes, ICE
  • Aerosolization: of vomit; people vomit violently without warning
  • Direct contact with infected people and fomites; secondary transmission
35
Q

List reasons why norovirus infections are so common

A
  • low infectious dose
  • resistant to disinfection
  • large human reservoir with prolonged shedding
  • strain-specific immunity is not longterm or cross-protective
  • many routes of transmission
  • genetic plasticity
36
Q

Host susceptibility to norovirus involves both acquired immunity and genetic resistance; some people are repeatedly susceptible with others are resistant. Susceptibility is based on what?

A
  • An individual’s ABH histo- blood group antigens expressed on gut epithelium
  • missing H type 1 epitope= resistant
  • O blood group is most susceptible
37
Q

Describe the structure of adenoviruses

A
  • nonenveloped
  • dsDNA
  • icosahedral capsid with 3 major proteins: hexons (serotypes), pentons, and fibers (subgroups)
38
Q

Describe the classification of Adenoviruses and which infect humans

A
  • divided into 7 subgroups (A-G) based on hemagglutination characteristics due to fiber proteins; different tropism
  • 57 human serotypes characterized by resistance to neutralization by antibodies to other known adenoviruses
  • Subgroup F, serotype 40 and 41 associated with GE in infants
39
Q

What is unique about culturing serotypes 40 and 41 andenoviruses?

A

-they are uncultivatable compared to other serotypes

40
Q

Clinical Pearls of Enteric Adenovirus

A
  • longer incubation time than others (8-10 days vs. 1-2 in others)
  • diarrhea lasts long on average (8-12 days)
  • occur year roung as epidemics
  • less likely to be febrile or dehydrating, and unlike other adenovirus types, respiratory symptoms are not prominent
41
Q

Astrovirus structural description

A
  • small round viruses
  • distinct start like appearance with 5 or 6 points
  • +ssRNA
  • naked
42
Q

Astrovirus classification

A
  • 2 genera: mamastroviruses (mammals) and avastroviruses (birds)
  • each genus with many species named after host: 8 serotypes of human astrovirus
43
Q

Astrovirus clinical pearls

A
  • detected in stools of children w. diarrhea in variety of settings: hospital, community, outbreaks
  • winter peak like rota in temperate climates (seasonality less clear in tropical areas)
  • most disease detected in young children, with clinical presentation like rotavirus but milder
44
Q

Best way to diagnose enteriv viruses?

A
  • NAAT

- GI viruses do not grow well in cell culture, and antigen detection is limited to rota and AdV40/41

45
Q

Treatment for viral GE

A
  • generally self-limited and no specific antiviral therapy

- supportive care to replace fluids

46
Q

How to prevent and control viral GE

A
  • live, oral vaccine for rotavirus
  • hand washing and good hygiene
  • identify and eliminate common source
  • employ infection control procedures
  • clean soiled surfaces and laundry
  • stop renewal of susceptible population

Microbiology Exam 2 (11 decks)

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