Transcript Rotavirus

Rotavirus


Rota – means wheel-like in greek
Double-stranded, segmented RNA
virus
Rotaviruses

80 nm in diameter.

Also found in other mammals and birds, causing diarrhoea.

Account for 50-80% of all cases of viral gastroenteritis.

Usually endemic, but responsible for occasional outbreaks.

Causes disease in all age groups but most severe symptoms in
neonates and young children.

Asymptomatic infections common in adults and older children.
Symptomatic infections again common in people over 60.

Up to 30% mortality rate in malnourished children





80% of the population have antibody against rotavirus by
the age of 3.
More frequent during the winter.
24-48 hr incubation period followed by an abrupt onset
of vomiting and diarrhoea, a low grade fever may be
present.
Diagnosed by electron microscopy or by the detection of
rotavirus antigens in faeces by ELISA or other assays.
Live attenuated vaccines now available for use in children

Globally, it is estimated that 1.4 billion
episodes of diarrhea occur in children less
than five years of age annually

Annually rotaviruses cause
– 5% of all deaths in children
– 527,000 deaths


80% of deaths are in infancy
> 100,000 in India
– 39% of childhood hospitalisations for
diarrhea




Rotaviruses are transmitted by the fecal-oral route.
Only 10 to 100 infectious virus particles are needed to
cause infection. This amount can readily be acquired
through contact with contaminated hands and
objects.
Large numbers of viruses are shed in fecal matter,
from 100 to 1000 particles per milliliter.
Hand-washing and sanitation does not work due to
the resistant nature of the virus. Similar
hospitalisation rates in countries with high and poor
sanitation


The most effective antiseptics against rotavirus are
alcohols, which have been found to reduce the number
of viruses on the hands by greater than 99%.
Tap water alone, or tap water with regular soap
reduces the titer by only 72-84%. ! Handwashing can
reduce the spread of the virus, but is an ineffective
means of eliminating it.
11 RNA segments

Rotaviruses are usually categorized into seven groups A-G,
with subgroups I and II based on the VP6 protein.



Rotavirus is further categorized into G and P serotypes.
The G serotype is specified by the glycoprotein VP7 of the
outer capsid, which is coded by viral genes 7, 8, and 9.
The P serotype is specified by protein VP4, also on the outer
capsid. It is a protease cleaved protein coded by gene 4 oft
he virus genome.




VERY resistant to
destruction
VP4 antigen: P
serotype;
11 human rotaviruses
VP7 antigen: G
serotype;
10 human rotaviruses
Commonly found
strains:
P[8]G1; P[8]G3;
P[8]G4;
and P[4]G2
VP1
VP1 is part of the inner core of the virus and one of three
proteins comprising the innermost of three viral layers. It is the
RNA-Dependent, RNA Polymerase for rotavirus.
VP2
This protein is the main structural component of the innermost
VP3
The third part of the inner core of the virus, VP3 acts as the
VP4
Along with VP 7, VP4 makes up the outer capsid of virus. It is an
88 kDa protein that dimerizes to create 60 spikes on virus
surface. VP4 is cleaved by the pancreatic enzyme trypsin to form
VP 5 and VP 8. VP4 and its cleavage products are associated
with cell attachment and invasion and cleavage is necessary for
infectivity. VP4 is antigenic and induces neutralizing antibodies.
The specific structure of this protein is used to determine the
rotavirus P serotype, as well as host specificity, virulence and
protective immunity.
layer.
mRNA capping enzyme.
VP5
VP5 is cleaved from the outer capsid protein VP4 in the
presence of trypsin. It remains bound to virion post cleavage,
and can be bound by neutralizing antibodies made to VP4. It is
membrane associated and functions to permeablize host cell
membranes to facilitate cell invasion.
VP6
VP6 is a structural component that comprises the middle capsid.
The specificity of this protein is used to determine the A-G
groupings, and I, II sub-groupings of rotavirus.
VP7
This 37 kD glycoprtein makes up the smooth portion of the
outer capsid. It can induce neutralizing antibodies and
determines the G serotype. It is also a highly variable portion
of the virus capable of reassortment and possible crossover
with animal strains of the virus.
VP8
VP8 is the second cleavage product of VP4; binds sialic acid and
acts the virus hemagglutinin
NS1-6
NS4
acts as an enterotoxin and causes diarrhea
Norovirus, Sapovirus
• Family Caliciviridae
• Non-enveloped RNA viruses
–with ss [+] sense RNA
• 27-35 nm in size
• Contains single capsid protein
Norovirus, Sapovirus
• Family Caliciviridae
• Non-enveloped RNA viruses
–with ss [+] sense RNA
• 27-35 nm in size
• Contains single capsid protein




Norwalk virus and “Norwalk-like”Norovirus
“Sapporo-like” viruses - Sapovirus
Vesivirus
Lagovirus


“winter vomiting disease” 1968,
Norwalk OH
Cause 40% of nonbacterial epidemics
– 45% foodborne, 52% shell fish
associated outbreaks

Explosive epidemics
– camps, cruise ships, nursing homes

Food borne illness
– raw shellfish
Characteristics of Noroviruses
Viruses
are small, capsid viruses distinguishable by capsid
morphology.

Body_ID:
B057003
Viruses
are resistant to environmental pressure:
detergents, drying, and acid.
Viruses
are transmitted by fecal-oral route in
contaminated water and food.
Viruses
Disease
cause outbreaks of gastroenteritis.
resolves after 48 hours, without serious
consequences


Survive on surfaces for several days
Survive in water chlorinated at routine levels
(up to 10 ppm)

Survive freezing, heating up to 60°C

Evidently survive in steamed shellfish

Asymptomatic infections- seroconversion but

asymptomatic shedding of virus

Low infective dose (~10 pfu)

Viral excretion during convalesence (~ 2
wk.)

Protective immunity short-lived

NLV cross protection?

Blood group antigens predilection?
Diagnosis

Specimen- stool, vomitus, food,
environmental swabs (during outbreak
investigations)

RT-PCR

Serology for epidemiologic purposes

Immune EM is less used
EPIDEMIOLOGY : Outbreaks




Cruise ships, schools,
nursing homes,
Can involve infants and
school-age children
Source usually is
contaminated food and
water (E.g. seafood-oyster
and shellfish, salads, cake
icing, raw fruit etc.)
Rapid secondary spread

CDC recommends environmental
disinfection of non-porous
surfaces with 1000 ppm bleach
solution (1 part bleach: 50 parts
water)
HUMAN ASTROVIRUS
Genus Astrovirus
Family Astroviridae
Human serotypes:
HuAstV 1-8

Small ss RNA virus

Non-enveloped

27-32nm in size

Round with an unbroken, smooth surface

EM appearance of a 5 or 6 pointed star within
smooth edge

Contain 3 structural proteins

Genome has been sequenced





Infants and children are most often affected
Elderly and immune compromised persons
also
Short incubation period 1-4 days
Nausea, vomiting, abdominal cramping and
watery diarrhea
Constitutional symptoms-fever, malaise,
headache

Endemic worldwide

True disease burden is not yet clear

Mainly in children <7 years of age

Transmission- person-to-person [fecaloral]

Outbreaks due to fecal contamination of
sea-food or water

EM (virus shed in stool in great
numbers)

EIA

RT-PCR