GI Tract Viral Infections Flashcards
List the viruses associated with gastroenteritis.
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.
Caliciviruses/Norovirus
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)
Rotaviruses
- • Acute gastroenteritis in kids less than 2 and adults
- Peak incidence = winter (“Winter Diarrhea”)
- 90% people over 4 yrs are seropositive
Adenoviruses
5-15% infections in U.S.
• Primarily in infants and children
• No seasonal outbreaks
• Usually sporadic outbreaks
Astroviruses
20-30% infections in U.S.
• Acute gastroenteritis in kids
• 75% of kids ages 3-4 are seropositive
• Higher incidence in winter
Coronaviruses
~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
Describe the major mechanism for the causation of diarrhea by Rotaviruses and Astroviruses.
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
Describe the mechanisms of transmission for the gastroenteritis agents
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
Name the most important therapeutic measure for gastroenteritis.
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
Coronavirus diarrhea is different from the other gastroenteritis viruses. What does this imply for the pathogenesis of the infection?
- Diarrhea can have blood or mucus
* Appears to cause inflammatory condition
Describe the mechanism of pathogenesis for enteroviruses. What factor is critical for CNS invasion resulting in meningitis or paralysis?
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
Characteristics of polio virus
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
Explain how polio is currently prevented and why the oral polio vaccine is no longer used in the United States.
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.
Describe the Hepatitis A vaccine
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
List the major disease syndromes caused by enteroviruses
Mild self-limiting illness with rash • Exception = polio Colds Aseptic meningitis Pericarditis/myocarditis • Coxsackie viruses Paralysis • Polio = can cause lethal paralysis Hepatitis
