GI Tract Viral Infections Flashcards

1
Q

List the viruses associated with gastroenteritis.

A

Enteroviruses (Picornaviridae) = not major cause of diarrhea:
o Poliovirus
o Coxsackie viruses
o Echoviruses (Enteric Cytopathic Human Orphan virus)
o Enterovirus

Gastroenteritis agents = primary symptom is diarrhea
o Caliciviruses/Norovirus = 20-30% infections in U.S.
o Rotaviruses
o Adenoviruses = 5-15% infections in U.S.
o Astroviruses = 20-30% infections in U.S.
o Coronaviruses = ~10% infections in U.S.

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2
Q

Caliciviruses/Norovirus

A

20-30% infections in U.S.
• Acute gastroenteritis in kids and adults
• No seasonal variation
• Usually seen as explosive outbreaks in institutions/communities (very infectious)

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3
Q

Rotaviruses

A
  • • Acute gastroenteritis in kids less than 2 and adults
  • Peak incidence = winter (“Winter Diarrhea”)
  • 90% people over 4 yrs are seropositive
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4
Q

Adenoviruses

A

5-15% infections in U.S.
• Primarily in infants and children
• No seasonal outbreaks
• Usually sporadic outbreaks

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5
Q

Astroviruses

A

20-30% infections in U.S.
• Acute gastroenteritis in kids
• 75% of kids ages 3-4 are seropositive
• Higher incidence in winter

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6
Q

Coronaviruses

A

~10% infections in U.S.
• Most frequent in kids <1 year
• Diarrhea can be associated with respiratory coronavirus infection
• SARS CoV or colds in children and adults
• Diarrhea = often has blood, less watery, and mucoid

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7
Q

Describe the major mechanism for the causation of diarrhea by Rotaviruses and Astroviruses.

A

Overall = gastroenteritis agents:
o Little to none intestinal inflammation or cell death
o Some shortening of microvilli → maladsorption

Rotavirus
o Viral toxin = NS4 protein
o Activates adenylate cyclase

Astrovirus
o Viral toxin = capsid
o Alters actin cytoskeleton → opens cell-cell junctions
• Note: for both rotavirus and astrovirus = can detect virus systemically, but symptoms are restricted to GI tract

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8
Q

Describe the mechanisms of transmission for the gastroenteritis agents

A

Primary mode of spread = fecal-oral
• Shed in large amounts from GI tract
• Shedding can last for weeks after symptoms

o Noroviruses = also have airbourne transmission
o Astroviruses = can be spread by vomitus
o Resistant to low pH

Incubation period = usually 1-3 days

Symptoms:
• Abrupt onset: vomiting, diarrhea, intestinal cramping
• May also have headache, myalgia, and low grade fever
• Watery diarrhea; usually no blood or mucus
• Exception = Coronaviruses

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9
Q

Name the most important therapeutic measure for gastroenteritis.

A

Prevention
o Hand washing
o Clean water; non-contaminated food

Supportive
o Maintain proper hydration
o Do not use agents that reduce peristalsis of gut (because infectious diarrhea)

Vaccine for Rotavirus
Part of routine infant immunizations
•	Given at 2, 4, and 6 months
•	Minimum age of 1st dose = 6 weeks
•	1st dose should be given at 6-12 weeks (until age 13 weeks)
•	Do NOT initiate series after 12 weeks
Do NOT give if:
•	Altered immunocompetence
•	Recent blood product recipient 
•	Acute, moderate to severe gastroenteritis or other acute illness 
•	Pre-existing chronic GI disease 
•	Infants with history of intussusception
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10
Q

Coronavirus diarrhea is different from the other gastroenteritis viruses. What does this imply for the pathogenesis of the infection?

A
  • Diarrhea can have blood or mucus

* Appears to cause inflammatory condition

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11
Q

Describe the mechanism of pathogenesis for enteroviruses. What factor is critical for CNS invasion resulting in meningitis or paralysis?

A

Multiply to high titers in GI tract
o Shed in feces even after symptoms gone
o Fecal-oral route

Cause disseminated infections in host
o Frequently = mild or asymptomatc

Stable at pH 3.0

Very hardy = can survive 70% ethanol, 5% Lysol, 1% detergents

Sensitive to 0.3% formaldehyde; 0.3-0.5 ppm chlorine

Inactivated at 50°C

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12
Q

Characteristics of polio virus

A

o Typical disseminated pattern
o About 2 week incubation

Usually causes aseptic meningitis or subclinical infection
• Invades CNS in 1-2% of infections
• Replicates in motor neurons (in anterior horn of spinal column, brain stem, motor cortex)
• Death of neurons → paralysis
• Occurs more frequently when primary infection occurs as teen or young adult

Patient death = usually due to paralysis of diaphragm and respiratory muscles → suffocation

Surviving patients usually regain some function in affected limb
• “Post-polio syndrome” = masks mild paralysis

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13
Q

Explain how polio is currently prevented and why the oral polio vaccine is no longer used in the United States.

A

Vaccines:
Salk vaccine
• Inactivated virus (contains all 3 serotypes)
• Currently recommended

Sabin vaccine
• Live attenuated virus (contains all 3 serotypes)
• Can revert to virulence = most common with Type 3 strain → cause infection
• Currently not recommended in U.S.

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14
Q

Describe the Hepatitis A vaccine

A

o Inactivated whole virus
o Pediatric and adult formulations
• Approved for patients ≥12 months

Recommended for:
•	International travelers
•	Men who have sex with men
•	Persons who use illegal drugs
•	Persons with occupational risk
•	Persons with chronic liver disease
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15
Q

List the major disease syndromes caused by enteroviruses

A
Mild self-limiting illness with rash
•	Exception = polio
Colds
Aseptic meningitis 
Pericarditis/myocarditis
•	Coxsackie viruses
Paralysis
•	Polio = can cause lethal paralysis 
Hepatitis
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