1 GI tract Flashcards
viruses infecting via the GI tract
(Primarily) Non-enteropathogenic viruses
- Enteroviruses (e.g. polioviruses)
- Hepatitis A virus
- Hepatitis E virus
Viruses associated with gastroenteritis
- Rotaviruses (group A)
- Enteric adenoviruses (type 40/41)
- Norovirus (NV)
- Astrovirus
- Calicivirus
- Aichi virus – new picornavirus
- Putative agents (e.g. pestiviruses)
Food or water borne viral disease clinical features
- 1-10 days watery diarrhoea (some viruses are very short, others can last a week or more)
- vomiting (aerosols contain virus which could contaminate food)
- abdominal discomfort
- fever
causes of food/water borne diseases
rotavirus
NV
enteric adenovirus
astrovirus
Acute Viral Gastroenteritis: 3 settings
- Epidemic gastroenteritis
- Sporatic gastroenteritis
- Sporadic Acute gastroenteritis
Epidemic gastroenteritis
semi-closed communities-food/water borne-NV
Sporatic gastroenteritis
in very young <2-normally caused by rotavirus but also enteric adenovirus
Sporadic Acute gastroenteritis
calicivirus
rotavirus
astrovirus
adenovirus
virus gastroenteritis resistance
All look similar with hard capsid shell to protect against outside world – resistant to lots, so can transmit
adenovirus symptoms
diarrhoea
adenovirus occurence
sporadic
adenovirus immunity
longterm
rotavirus symptoms
diarrhoea and vomiting
rotavirus occurence
sporadic
rotavirus immunity
longterm
astrovirus symptoms
nonspecific GI
astrovirus occurence
sporadic
astrovirus immunity
longterm
calicivirus symptoms
D+V
calicivirus occurence
sporadic
norovirus symptoms
D+V
calicivirus immunity
longterm
norovirus occurence
outbreak
norovirus immunity
shortlived
modes of transmission
faecel-oral
indirect
direct
faecel-oral transmission
ingestion then replication in intestine then excreted is then ingested again
indirect transmission
- from contaminated food/water source (ingested orally by new host, from food or water -food borne)
- transferred to food/water via ill worker (food-borne)
direct transmission
person to person
Infected/ill person can infect another person directly
Vomit (aerosol/indirect)
Direct contact (person to person)
infectious dose amount
normally low 10-100 particles
clinically important Gastroenteritis Viruses
norovirus
rotavirus
both are transmitted faecally
outbreaks of norovirus
2013 Oyster outbreak (US), 2007 School sandwiches
projectile vomiting
another mechanism of transmission
Aerosols spread by projectile vomiting contaminate food and also can transmit virus directly though person to person spread
Molluscan Shellfish e.g. oysters
- The foodstuff most commonly linked with NV-associated gastroenteritis
- Filter-feed
- Concentrate virus from sewage-contaminated waters
- Eaten raw or steamed
Clinically important Gastroenteritis Viruses
foods associated
food-borne viruses
- Fresh fruit, salad items, sandwiches, eggs, frosting on baked goods
how is food contaminated
- handling by an ill food worker
- washing of food using contaminated water
- items that followed the cooking process
rotavirus findings
- Causes severe diarrhoea among infants
- Transmitted though faecal-oral route through infected hand, utensils possibly through respiratory route
- Single most important cause of diarrhoeal illness worldwide.
- Cause severe dehydration
- Some Vaccines available
rotavirus morphology
- a genus within the family reoviridae:
- 60 spikes extend from the smooth surface of the outer shell (hard capsid shell)
- Resemble a wheel hence rota
- Non-enveloped – can propagate in the environment
Rotavirus – Genome
- 11 segments of double-stranded RNA
- structural viral proteins (VP):
1. outer capsids: VP4 and VP7 (antigens we make vaccines against)
2. core: VP2, VP6, VP1, VP3 - nonstructural proteins (NSP): NSP1-5
Rotavirus – Classification
group A group B group C group D, E and F serotypes within these groups
group A
Significant diarrhoeal illness in the young, most important, vaccines are made to serotypes within this group
group B
Annual epidemics in adults especially in China
group C
Sporadic child cases, also in outbreaks
group D, E and F
In animals thus far
Serotypes within rotavirus group A - vaccines
- defined by cross-neutralization with polyclonal antibodies of antigenic specificities (glycoproteins)
- VP4 antigen: P antigen (protease-cleaved protein)
- serotype; 8 human rotaviruses
- VP7 antigen: G antigen (glycoprotein)
Rotavirus – Epidemiology
primary trasmission
fecal-oral
rotavirus transmission
ingestion of contaminated food or water and contact with contaminated surfaces
rotavirus high rates illness
among infants and children below 2 years old, but mild among adults
where does Rotavirus effect in body
Infects upper two-third of duodenal epithelial cell
how does rotavirus effect body
Viruses released into lumen and undergo further replication in distal areas –> enterocyte death
effects of rotavirus on body
Malabsorption
NSP4 toxin = Epithelial permeability ↑
rotavirus pathogenesis – malabsorption
Reduced absorptive surface, water passes through and end up with diarrhoea
Denudation of microvilli; shortening, flattening and atrophy of villi; invasion of villi by rotavirus causing ischaemia and shortening
rotavirus diagnosis
- Antigen Enzyme Immunoassay (EIA) of stool specimens
- RT-PCR (RT – reverse transcription step because it is RNA, to get back to DNA)
rotavirus treatment
- Non-specific treatment: oral rehydration therapy to prevent dehydration- problem in the developing world-cause of death
- Intravenous fluid is required in severe infant cases
- Immunization by vaccines
Rotashield effectiveness
Very effective vaccine but was taken off because of the intussusception
5-10X die from rotavirus then the side effect, but was banned
noroviruses causes
gasteroenteritis nausea vomiting, diarrhoea abdominal pain
norovirus transmitted by
Fecal-oral or person to person, projectile vomiting
norovirus source
water often from wells
recreational lakes
swimming pools
water stored aboard cruise ships
norovirus treatment
No vaccine
norovirus immunity
short lived
norovirus culturing
non-culturable (can’t grow it in tissue culture cells)
norovirus symptoms
- disease is self-limiting
- characterized by nausea, vomiting, diarrhoea, and abdominal pain
- Headache and low-grade fever may occur
norovirus detection
Detected by electron microscopy or Antibody production or PCR
norovirus infectious dose
unknown but presumed to be low
Criteria for suspecting an outbreak due to NV
- Stool cultures > Negative for bacterial pathogens > No viral culture - Duration of illness > mean 12-60 hours - Vomiting in >50% of cases
NVs Epidemiology – incidence
NVs (Small Round Structured Viruses) are the most common agent responsible for outbreaks of infectious intestinal disease, responsible for approximately 1/3 of adult outbreaks
where do norovirus outbreaks occur
places of high population density
prevention of norovirus
- Handwashing
- Proper sanitation
- Safe drinking water and food
