Gastroenteritis Viruses2

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gastroenteritis viruses




-Gut: both entry route and the target tissue. Replicate + Remain + Induce
symptoms in the gut.
-Rapid spread via feacal-oral route due to lack of hygiene.
-the third most common killer disease is the gastroenteritis associated diarrhoea
disease. 200 million people suffering from diarhoea
-Gastroenteritis viruses: rotaviruses, astroviruses, adenoviruses, caliciviruses
(norovirus + sapovirus)
-Detection and Diagnosis: gold standard is culturing but most enteric viruses
grow poorly in culture.The main are: electron microscopy, PCR, ELISA
Electron microscopy: rapid and catch-all method.
BUT low sensitivity,
trained operator required,
clear and distinctive virus morphology required,
good sample preservation required.
PCR and ELISA: Cheap, convenient and rapid
Must know what virus to search for.
Can only detect characterized virus
Requires antisera for ELISA
Sequence knowledge for PCR
Food Safety: Enteric viruses infect at very low doses.
Rarely detecable levels in food
Routine food screening not possible
-Infant diarrhoea
-Occur in places having water supply
-Transmission via feacal-oral route
-From asymptomatic health care staff to
-Chronic infection in immunedeficient

-outbreaks in instutions; nursery and hospital. (virus resistant to chemical
-member of Reoviruses  reo= respiratory enteric orphan; icosohedral with
dsRNA genome isolated from respiratory tract and enteric tract of human but
cause no diseases.
-dsRNA, 11 segments
-segmentation allows reassortment between different strains. 6 serotypes
-each segment encodes one protein, only one encodes 2 proteins
-6SP + 6NSP
-VP1/VP3: associated with genome, found in the core. VP1: RNA dependent RNA
polymerase. VP3: guanylyl and methyl transferase.
-Triple Layer:
First Layer: smooth core mainly of VP2, with some VP1 and VP3
Second Layer: rough surface with VP6
Third Layer: smooth coat of VP7 perforated with channels
Outer surface: spikes of VP4
-Attack enterocytes; columnar epithelium at the apices of the villi in duodenum
and upper ileum.
-Loss of villi apices leads to mal absrorption. Reduced absorption of
salt/water/sugar from the gut but rapid regeneration after attack. Damage to
tight junctions allows fluid leakage;secretion of water by secretory cells leads to
diarrhoea and dehydration.
-VP4 and VP7 for attachment – entry by direct penetration or endocytosis.
-Upon entry, outer layer removed. Only inner and middle layers remained.
-Entry of rNTPs via channels.
- VP1 synthesize 11 (+)mRNA – capped by VP3.
-newly sythesized mRNA is exported without poly(A) through channels.
-cytoplasmic translation
-core assembled and +RNA enters – recognition of unique sequences of segments
-VP1 synthesize (-)RNA to yield dsRNA in the core.
-late transcription to produce SPs.
-virion buds through ER. temporary envelope cleaved by viral protease.
-virion released by exocytosis/lysis.
Symptoms: vomitting, diarrhoea, fever, dehydration
NsP4 rotavirus endotoxin: assists virus maturation – budding through ER; alters
plasma membrane permeability and destablizes them promoting cell death. It
also increases chloride secretion.
it has no effect on cAMP level but mobilizes Ca+2 in ER.
alone induces diarrhoea
symptom severity is dependent on age
Ab to NsP4 is protective
Peptides from NsP4 are immunologically active
NsP4 in ER memberabe: hydrophobic sections anchor NsP4 in the

oligamerisation domain mediates intermolecular
association – NSP4 aa95-137. Forms tetrameric coiled coil on which calcium binds
internally. This region contains pathogenic region.
cell lysis allows proteolysis of extended regions.
-80% seropositivity by 3yr old – 100% by 5. Immunity acquired by primary
infection. Sequential infections boost immunity. Reinfections may be symptom
-6 serotypes : A-F
-diagnosis : identifiable partcicles + large numbers for EM detection. By PAGE,
ELISA and Agglutination methods
-no specific therap. vaccines in trial.
-Infect wide range of hosts: mammals, birds, fish, reptiles
-2 infect humans: Noroviruses and Sapoviruses. Number of strains infect humans
(named after places of discovery): Norwalk virus,Hawai virus, Taunton and Snow
mountain viruses
-Study problems: do not replicate in lab conditions.
knowledge derived from non-human caliciviruses replicating in
cell culture
studies relied on volunteers: sequencing of Norovirus genome
from rt-PCR of
stools of infected volunteers
- 32 cup-like indentations on the surface
-NON-enveloped, icosohedral symetry
- (+)ssRNA with VPg protein linked to 5’ and poly(A) tail linked to 3’. 3 ORF.
-Translation produces a large polyprotein processed into SP and NSPs.
-RNA replicates in cytoplasm. Only one subgenomic RNA – translated into
structural proteins
ORF1: 2CATPase , 3Dpol , 3Cpro

processed by 3Cpro

- Transmission via feacal-oral route or through inhalation of aerosols from
vomitting. Outbreaks from contaminated food/water
-Sudden onset with abdominal pain and fever
-Vomitting, projecticle vomitting, diarrhoea
-incubation period 18-48hr.

-Diagnosis: EM: difficult; fewer in number, less distinctive in appearance, small
and hard to distinguish from the background. RT-PCR
-2002 Norovirus Outbreaks:
many hospitals forced to close in whole or in part (UK, Ireland, Canada)
waterborne outbreaks in Canada
outbreak in armed forced in Afganistan
cruise ship outbreaks UK – USA – New Zealand
 childhood infection
 Ab+ by age 12.
 outbreaks in institutional settings
 foodborne transmission rare


peak incidence in teens/young adults
low infectious dose
seasonal preference : winter vomitting disease
foodborne transmission (20-40%) common (water, shellfish, salads and
fruits) + aerosol transmission
43% of intestinal disease is caused by Norovirus
single major cause of nonbacterial gastroenteritis

-star like distinct morphology
-outbreaks of diarrhoea in children (vomitting is not dominant feature)
-peak incidence in winter
-8 serotypes in human astrovirus. type 1: the most common (7%), type 4; second
most common. Exposure of adults to type 4 is via sea-water. Type 6: foodborne
-50%seropositivity by the age 7, 75% by age 10
-Diagnosis: ELISA
-generally short-mild lived diarrhoea
-Large DNA virus
-Found universally in water
-Used to monitor feacal contaminations

-waterborne transmission: -rarely foodborne
-releationship between respiratory and eye infections
-diagnosis : EM
-grow well in the gut
-seropositivity: 20% by 6 months old, 50% 40months old
- intake of water up to 2litres/day. net secretion into gut is 7litres/daily. Must be
reabsorbed to prevent dehydration.
-virus targets the top of villus – containing differentiated cells and ion pump
actively absorbing water. Below are undefirrentiated cells which are
nonfunctional. So when apices of villi are destroyed, only nonfunctinal cells
remain which cannot absorb water.
When apices are targeted, easier to generate. But calicivirus and astrovirus
target basal part which are difficult to regenerate.
Infction generates a wave of virus replication passing along the intestine.

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