Viral gastroenteritis Flashcards
Signs and symptoms of viral gastroenteritis
Acute onset watery diarrhea (no mucus or blood) +/- vomiting
Short incubation period
Short duration
Highly transmissible
Acute gastroenteritis in the US compared to world
US:
2nd only to common cold in frequency
1-2 episodes/year
Worldwide:
6-7 episodes/year
Lots of deaths
Pathophysiology of viral gastroenteritis
Local infection of intestinal epithelial cells
Malabsorption due to virus killing mature enterocytes
Local villus ischemia leading to diarrhea
Viral enterotoxin changing the transepithelial fluid balance
How do diagnose viral gastroenteritis
Usually clinical
PCR (mutiplex Stool real time PCR)
Treatment for viral gastroenteritis
Oral rehydration
Prevention of viral gastroenteritis
Hygiene: handwashing, food preparation
Sanitation: toilets, water supply, diaper changing
Environmental cleaning
Isolation of patients
Vaccines: rotavirus available, norovirus in development
Caliciviruses: Phylogeny
Sapovirus (humans)
Norovirus
Many human serotypes:
GII.4 Sydney: first detected 2012 in Australia
Principal cause of outbreaks in US
Variants arise by mutation or recombination
Norovirus structure
Small round ssRNA virus, 27nm in diameter, with cup shaped indentations
Naked, non-enveloped
Viral-encoded protease cleaves viral polyproteins:
Difficult to grow in culture
Symptoms of norovirus
1/3 asymptomatic but shedding virus
Vomiting, watery diarrhea, nausea, cramping
Malaise, headache, myalgia, low-grade fever
Occasionally dehydration
Spread of norovirus
Person-to-person (fecal-oral spread)
Contaminated surfaces
Foodborne (esp shellfish)
Waterborne
Shedding after symptoms resolve
Incubation and duration of norovirus infection
FAST!
Incubation: 15 hrs to 2 days
Duration of symptoms: 1-2 days
Epidemiology of norovirus
“Cruiseship virus”
Has replaced rotavirus as #1 in areas where rotavirus vaccine in use
Most common cause of diarrheal outbreaks in older children and adults
Rotavirus
Huge problem in developing world
Vaccine avaialble
Rotavirus structure
11 double stranded RNA genome segments
Each segment encodes one viral protein (VP)
Non-enveloped, but three protein shells
Outer capsid layer: acid stability
Composed of VP7 with VP4 spikes: induce neutralizing antibody
Inner capsid layer
Contains VP6: major rotavirus group antigen
Innermost core: VP2
Reassortment
Reassortment allows introduction of segments from animal
rotavirus into human rotavirus, causing epidemics
Rotavirus Pathogenesis
Affects small intestine
Replicates in villus epithelial cells
Mononuclear inflammation
Villus shortening, stunting
Mechanism causing diarrhea is unclear
? Decreased absorptive properties of denuded villi
? NSP4 enterotoxin
High viral titers shed in stool (>10¹¹ viral particles/mL)
Rotavirus Enterotoxin: NSP4
Maybe neurotoxin?
Causes diarrhea in animal studies
Clinical manifestations of rotavirus
Up to 50% infections are asymptomatic
Symptomatic infection: abrupt onset fever and vomiting, followed by diarrhea
Stools are explosive, watery, nonbloody
Frequently leads to dehydration in children
Incubation and Duration of rotavirus
Symptoms last 4-8 days, self-limited
Incubation period: 1-3 days
Peak viral shedding on day 3, can be prolonged (> 3 weeks)
Rotavirus: Burden of Disease and epidemiology
Rotavirus is the single most important cause of severe infantile gastroenteritis worldwide
Before rotavirus vaccines in US: Up to 180,000 hospitalization/yr 20-40 deaths/yr In developing countries: 500,000 deaths/yr
Common disease of infants and young children
Treatment and prevention of rotavirus
Treatable by oral/IV rehdration
Preventable by available rotavirus vaccines
Spread of rotavirus
Fecal-oral
Remain infective for long periods on surfaces
Water, food, respiratory transmission less frequent
SEASONAL
Rotavirus: Current Vaccines
RotaTeq (RV5): Pentavalent live bovine rotavirus vaccine
Contains outer capsid proteins of 5 human RV strains made by reassortment with bovine RV genome segments
75% protective against disease, 98% protective against severe disease
Oral, 3 doses (2, 4, 6 months)
Rotarix (RV1): Monovalent live human rotavirus vaccine
Provides cross-protection against other strains
85% protective against severe disease
Oral, 2 doses (2, 4 months)
Interesting that the monovalent still offers good protection
US: # children hospitalized for rotavirus reduced by ~85%
What are the adenovirus serotypes that can cause gastroenteritis
40 and 41
In immunocompromised pts we think about it
Duration of adenovirus
5-12 days
Astroviruses
Small non-enveloped single stranded RNA virus, star-shaped capsomers
Trypsin necessary to activate infectivity
2-8% of diarrheal ds in children
Excreted for prolonged periods in immunocompromised
Person-to-person and foodborne spread
Outbreaks in daycares, nursing homes, school cafeterias, nursing homes
