Download ROTAVIRUS

Viruses Associated with
Gastroenteritis
Ghazi Jamjoom
VIRAL AGENTS CAUSING
GASTROENTERITIS
Major Viruses
1. Rotavirus
2. Enteric adenoviruses
3. Noroviruses :
a. Norwalk-like viruses
b. Calicivirus
c. Astrovirus
Noroviruses
Norwalk-like
viruses
Caliciviruses
Astroviruses
other
viruses
Viruses associated with
gastroenteritis (cont) :
Other viruses (minor):
• Coronaviruses
• Parvoviruses
• Pestiviruses
• Toroviruses
ROTAVIRUS
Family Reoviridae
Genus Rotavirus
ROTAVIRUS
• First isolated in 1973 from children with
diarrhea
• EM identification from duodenal biopsies
• Human and animal strains
Rotavirus
Rotavirus- EM Structure
ROTAVIRUS
•
60-80nm in size
•
Non-enveloped virus
•
Double capsid
•
EM appearance of a wheel with radiating spokes
•
Icosahedral symmetry
•
double stranded (ds) RNA in 11 segments
(double – double)
ROTAVIRUS- 3D STRUCTURE
Viral Structural Proteins (VP)
• Outer structural proteins - VP7 and VP4
VP7=glycoprotein
VP4=protease-cleaved, P protein, viral hemagglutinin,
and forms spikes from the surface
• Inner core structural proteins VP 1, 2, 3, 6
• VP6 is an important antigenic determinant
• Genome is composed of 11 segments of double-stranded RNA,
six structural
coding for
proteins
five nonstructural
•
Seven serological groups have been identified (A-G), three of
which (groups A, B, and C) infect humans .
STRUCTURE
Gene coding assignment
Classification
•
Groups, subgoups, serotypes based on viral capsid
proteins
•
7 Groups (A through G)
•
Group A is the most common and has 2 subgroups
•
10 human serotypes based on G protein (VP 7)
•
8 P protein serotypes
Classification (contd.)
• Electropherotypes
mobility of RNA segments by PAGE
Used in epidemiologic studies
Rotavirus - Properties
• Virus is stable in the environment
• Relatively resistant to handwashing agents
• Susceptible to disinfection with 95% ethanol,
‘Lysol’, formalin
Pathogenesis
• Targeted host cells- mature enterocytes lining the
tips of intestinal villi
• Intermediate/infective sub-viral particle (ISVP)
produced through proteolysis
• Enter host cell by endocytosis
• Virus replicates in the host cell cytoplasm
Replication
• mRNA transcription with viral RNA polymerase
• Capsid proteins formed
• mRNA segments formed, assembled into immature
capsid
• mRNA replicated to form double stranded RNA
genome
Histopathology
• Mature enterocytes lining the tips of intestinal
villi are affected
• Villous atrophy and blunting
• Death of the mature enterocytes
Histopathology
Epidemiology - Worldwide
• Millions are affected
• 600,000-850,000 deaths/year
• A major cause of diarrhea-associated
hospitalizations
• Seroprevalence studies show that antibody is
present in most by age 3y.
RotavirusWorldwide distribution
(source- centers for disease control and prevention)
Estimated Global Distribution of The 800,000 Annual Deaths
Caused By Rotavirus Diarrhea
Epidemiology : U.S.
•No. of children under 5y. affected ~ 2.7 million
•Physician visits per year ~ 500,000
•Hospitalizations per year ~ 50,000
•Deaths per year ~ 20 - 40
•% cases w/ dehydration ~ 1-2.5%
Epidemiology
• Age- 4mo - 2 years
Protection of younger infants through transplacental
antibody transfer
• Asymptomatic infections are common, especially in
adults
• Nosocomial infections
• Outbreaks
Epidemiology (contd.)
• Seasonality
Winter months (Nov. through May in US)
Gradual spread W to E
Year-round in the tropics
• Incubation period - thought to be <4 days
Epidemiology : U.S.
(Source- centers for disease control and prevention)
Epidemiology (transmission)
• Mainly person to person via fecal-oral route
• Fomites
• Food and water-borne spread is possible
• Spread via respiratory route is speculated
Epidemiology (spread)
• Contagious from before onset of diarrhea to a few
days after end of diarrhea
• Large amounts of viral particles are shed in
diarrheal stools
• Infective dose is only 10-100 pfu
EPIDEMIOLOGY
Differences in Groups
• Group A infections are most common
• Group B has been associated with outbreaks in
adults in China
• Group C is responsible for sporadic cases of
diarrhea in infants around the world
Clinical Features
• Incubation period - thought to be <4 days
• Fever- can be high grade (>102F in 30%)
• Vomiting, nausea precede diarrhea
• Diarrhea
- usually watery (no blood or leukocytes)
- lasts 3-9 days
- longer in malnourished and immune deficient indiv.
- NEC and hemorrhagic GE seen in neonates
Mechanism of diarrhea
• Watery diarrhea due to net secretion of
intestinal fluid
• Activation of the enteric nervous system possible role of enterotoxin
Clinical Features (contd.)
• Dehydration is the main contributor to
mortality.
• Secondary malabsorption of lactose and fat,
and chronic diarrhea are possible
• Recovery is usually complete.
• However, severe diarrhea without fluid and electrolyte
replacement may result in dehydration and death .
Immunological Aspects
• Immunoglobulin (Ig) A , in the lumen of the gut
immunity
to infection .
• Actively or passively acquired antibodies (including antibodies in
colostrum and mothers milk)
lessen the severity of disease
but does not consistently prevent reinfection .
• Absence of antibody
and diarrhea .
small amounts of virus
infection
Diagnosis
• Antigen detection in stool by ELISA, Latex
Agglutination (for Group A rotavirus)
• EM- non-Group A viruses also
• Culture- Group A rotaviruses can be cultured in
monkey kidney cells
• Serology for epidemiologic studies
Treatment and Prevention
• TreatmentSupportive - oral, IV rehydration
• PreventionHandwashing and disinfection of
surfaces
Vaccine
• Live tetravalent rhesus-human reassortant
vaccine (Rotashield)
• Licensed for use in August 1998
• Removed from the market in October 1999
due to risk of intussusception
• Cases were seen 3-20 days after vaccination
• Approx. 15 cases/1.5 million doses
• New vaccine from bovine rotavirus under
trial
Production of rhesus rotavirus (RRV), human rotavirus (HRV) x rhesus rotavirus
(RRV)reassortant quadrivalent vaccine wit VP7 serotype 1, 2, 3, and 4 specificity
GASTROENTERITIS
DUE TO ENTERIC
ADENOVIRUS
GASTROENTERITIS DUE TO
ADENOVIRUS
• Types 40, 41
• Belong to serogroup F
• Some cases due to types 31, 3, 7
Diarrhea due to
Enteric Adenovirus
• Age <4 years
• Year round
• Spread via fecal-oral route
Clinical features of Enteric
Adenovirus gastroenteritis
• Incubation period 3 -10 days
• Diarrhea lasts for 10 -14 days
• Can also cause intussusception, mesenteric
adenitis, appendicitis
Diagnosis- Enteric adenoviruses
• Isolation requires special media-Graham
293
• ELISA for rapid detection is available
HUMAN
CALICIVIRUSES
HUMAN CALICIVIRUSES
(HuCV)
•
Belong to Family Caliciviridae
•
Non-enveloped RNA viruses
with ss RNA
•
27-35 nm in size
•
Contain a single capsid protein
HUMAN CALICIVIRUSES
•Genomic analysis divides it into 4 groups
•Human caliciviruses belong to 2 genera
CLASSIFICATION OF HuCV
NLV (Norovirus)
Norwalk virus
Hawaii virus
Snow Mountain virus
Montgomery county virus
Taunton (England)
SLV (Sapovirus)
Sapporo virus
Manchester virus
Houston/86
London/92
Morphology of HuCV- typical
• Typical morphology
• 32 cup-like depressions
• EM appearance of “Star of David”
E.g.- Sapporo-like viruses
HUMAN CALICIVIRUSES - SLV
Morphology of HuCV- atypical
• Atypical morphology
• Smooth surface
• Small Round Structured viruses
E.g.- Norwalk-like viruses
SRSV- NORWALK VIRUS
CLINICAL FEATURES
• Adults and Children
• Usual incubation Period is <24 hours
(ranges from 12hrs. to 4 days)
• Short duration of illness <3 days
• Nausea, vomiting, fever, headache
• Abdominal cramping
• Watery diarrhea
Epidemiology-Noroviruses
• Worldwide distribution
• >23 million cases/year in the U.S.
• Major cause of foodborne outbreaks of GE
• Most people have had infections by age 4
years (by seroprevalence studies)
Spread of Norwalk virus
A. Person-to-person Fecal-oral spread
(stool/vomitus)
B. Fecal contamination of food or water
C. Spread through fomites?
Epidemiology-Noroviruses
• Asymptomatic infections- seroconversion but
asymptomatic shedding of virus
• Low infective dose
• Viral excretion during convalesence
(up to 2 weeks)
• Ability to survive in water chlorination at
routine levels
Epidemiology of Outbreaks
• Cruise ships, schools, nursing homes, etc.
• Can involve infants and school-age children
• Source usually is contaminated food and water
(seafood-oyster and shellfish etc.)
Diagnosis- Human Caliciviruses
• Specimen- stool , vomitus, environmental swabs,
[not yet on foods]
• Immune EM
• RT-PCR in state public health labs.
• Serology for epidemiologic purposes
HUMAN
ASTROVIRUS
ASTROVIRUS
• Described in relation to an outbreak of
gastroenteritis in 1975
• Detected by EM
• Immunologically distinct from Human Caliciviruses
• Belong to family Astroviridae
• 8 human serotypes are known
ASTROVIRUS- structure
• 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
ASTROVIRUS- EM
STRUCTURE
ASTROVIRUS - Epidemiology
• Worldwide
• Mainly in children <7 years of age.
• Transmission person-to-person via
fecal-oral route
• Outbreaks due to fecal contamination of
sea-food or water
ASTROVIRUS - Clinical Features
• Infants and children are most often affected
• Short incubation period 1-4 days
• Nausea, vomiting, abdominal cramping and watery
diarrhea
• Constitutional symptoms-fever, malaise, headache
ASTROVIRUS - Diagnosis
• EM (virus shed in stool in great numbers)
• EIA
• RT-PCR
Rotaviruses
Ghazi Jamjoom
• Twenty-five years ago, little was known
about the causes of diarrhea, which kills an
estimated 3 million infants and children
worldwide every year.
• Scientists knew that bacteria and parasites
were implicated in only approximately 10 to
20 % of all cases of diarrhea..
• In 1973,, researchers in Australia
discovered a virus in infants with severe
diarrhea and named it “rotavirus” for its
wheel-like shape.
• One year later, NIAID researchers were
the first to identify rotavirus in the United
States.
Rotavirus Biology
• Rotaviruses belong to the family Reoviridae ,
genus Rotavirus.
• They have a characteristic wheel-like
appearance when viewed by electron
microscopy.
• Nonenveloped, double-shelled
Group A rotaviruses
•
Endemic worldwide (represents > 95% of
currently identified strains in humans )
• The leading cause of severe diarrhea among
infants and children .
•
Accounts for about half of the cases
requiring hospitalization.
Group B rotavirus,
•
Also called adult diarrhea rotavirus or
ADRV
• Has caused major epidemics of severe
diarrhea affecting thousands of persons
of all ages in China.
Group C rotavirus
•
•
Has been associated with rare and sporadic
cases of diarrhea in children in many
countries.
• First outbreaks were reported from Japan
and England
• Subgroups classification based upon
neutralization epitopes of the outer capsid proteins,
VP4 and VP7
Antigenic specificity of VP7
G serotypes
Antigenic specificity of VP4
P serotypes
Fourteen G serotypes and twenty one P serotypes have
been detected in humans.
Neutralization assays measure reactivity
predominantly to VP7 proteins.
Distribution of Rotavirus Strains From A
Global Collection of 2,748 Strains.
Transmission
•
Rotavirus infection is very contagious .
•
Viral particles pass in the stool of
infected persons before and after they
have symptoms of the illness .
•
Spread is by the oral-fecal route
and tables) and is not killed by standard
fectants... children forget to wash their hands often
gh, especially before eating and after using the toilet.
t
Get infected
d food handlers may contaminate foods that require
ing and no further cooking, such as salads, fruits.
• The infective dose is presumed to be 10-100 infectious viral
particles.
Because a person with rotavirus diarrhea often excretes large
numbers of the virus (108-1010 infectious particles/ml of
feces), infection doses can be readily acquired .
• Asymptomatic rotavirus excretion has been well
documented
may play a role in perpetuating
endemic disease .
N.B some have reported low titers of virus in respiratory
tract secretions and other body fluids..
Epidemiology
Rotavirus is the single most important cause of
life-threatening diarrhea in children younger
than 2 years.
•
• Affects approximately 130 million infants and
children worldwide.
In the United States alone, rotavirus causes
more than 3 million cases of childhood
diarrhea each year, leading to an estimated
55,000 to 100,000 hospitalizations and 20 to
100 deaths.
•
Who catch the infection ?
• Humans of all ages are susceptible to rotavirus infection,
although Children , premature infants, the elderly,
and the immunocompromised are prone to more severe
symptoms caused by infection with group A rotavirus.
•
An infant’s first bout of diarrhea from
rotavirus is the most severe ,
subsequent reinfections decrease in
severity.
These findings indicated that infants
gradually develop partial immunity to the
virus and that a vaccine might prevent
the disease.
• Temporary lactose intolerance may occur.
• NSP4 protein may act in a toxin-like manner
Neuronal
alteration in
water absorption
Release of neuronal
activators
• Loss of the ability to absorb water
of water and loss of ions
Calcium ion influx
into enterocytes
net secretion
watery diarrhea
Watery diarrhea
isotonic) and may lead to
death .
dehydration (most commonly
metabolic acidosis and
Symptoms and Signs
• The incubation period ranges from 1-3 days .
• Symptoms often start with vomiting followed by 4-8 days of
diarrhea.
• Some may have a slight rise in temperature .
Immunological Aspects
• Immunoglobulin (Ig) A , in the lumen of the gut
immunity
to infection .
• Actively or passively acquired antibodies (including antibodies in
colostrum and mothers milk)
lessen the severity of disease
but does not consistently prevent reinfection .
• Absence of antibody
and diarrhea .
small amounts of virus
infection
• Infection in infants and small children is generally symptomatic .
• In adults infection is usually asymptomatic .
• Asymptomatic rotavirus infections are common in neonates
because of passively acquired maternal immunity , breast
feeding , and possible infection with less virulent strains
Diagnosis
(EIA)
1) Identification of the viral antigen in the patient's stool
latex agglutination
most widely used screening test for clinical specimens .
2) Electron microscopy (EM)
3) polyacrylamide gel electrophoresis (PAGE) is used in some laboratories for RNA
typing.
4) A reverse transcription-polymerase chain reaction (RT-PCR) has been developed to
detect and identify all three groups of human rotaviruses.
• Serotypes can be identified using monoclonal antibodies
against VP7 and VP4.
• Neutralization is detected on tissue cultures as a CPE
Antigenic specificity of VP7
G serotypes
Antigenic specificity of VP4
P serotypes
Treatment
• Treatment is nonspecific and consists of :
1) Oral rehydration therapy to prevent dehydration.
2) About one in 40 children with rotavirus gastroenteritis will
require hospitalization for intravenous fluids .
• For persons with healthy immune systems, rotavirus gastroenteritis is
a self-limited illness, lasting for only a few days.
prevention
• Even in the cleanest environments with the best hygiene, most children
still become infected with rotavirus before age 4 or 5.
• Total prevention of the spread of rotavirus is virtually impossible.
• In hospitals health officials control rotavirus outbreaks by isolating
infected patients and by ordering strict hand-washing procedures.
Rotavirus
Vaccine
Rotavirus vaccine
• Scientists knew that although many strains of rotavirus exist, only four
cause the majority of diarrhea cases in young children in the United
States.
• Aiming for prevention : NIAID researchers developed a vaccine
(RRV-TV) designed to protect against the four strains of rotavirus .
•
During the 1970s, NIAID scientists analyzed the genetic material of
rotavirus, Identified two important proteins , VP4 and VP7 produced
by the genes , and determined the function of these proteins.
• Proteins on the surface of the virus were found to be critical for triggering
an immune response in the body against rotavirus.
• NIAID researchers focused on these proteins to develop a vaccine.
Tetravalent Oral Live-Attenuated Vaccine
• The oral vaccine contains four different, live attenuated viral strains,
serotypes ( 1,2,3,4) .
• One strain (serotype 3) is an unmodified rhesus monkey rotavirus
(RRV) which does not cause disease in humans
• The other three are made by reassortment (genetic recombination)
of that monkey RRV with three human rotaviruses of serotypes
1,2,4.
• Each reassortant vaccine strain contains 10 monkey RRV genes and
the VP7 gene for one serotype of the human rotavirus envelope
proteins:
VP-7 (serotype 1) , VP-7 (serotype 2) , VP-7 (serotype 4)
• The combined vaccine provided comprehensive protection
against the four serotypes (1,2,3,4)
• Studies showed that high doses of the RRV-TV vaccine, designed to
protect against four strains of rotavirus, were very effective in
preventing severe, dehydrating rotavirus disease.
• Breast-feeding did not interfere with the effectiveness of
the rotavirus vaccine
ensuring good nutrition in infants
• In August 1998, the first live attenuated rotavirus vaccine
(Rotashield{registered} {Wyeth Lederle Vaccines and Pediatrics}) was
approved for use in infants by the Food and Drug Administration. The
Advisory Committee on Immunization Practices has recommended that
this vaccine be given as a three-dose schedule to infants aged 2, 4, and 6
months.
•However, on July 15, 1999, the US Centers for Disease Control and
Prevention (CDC) recommended that doctors stop giving the
rotavirus vaccine to infants.
• On October 22, 1999, the Advisory Committee on Immunization
Practices voted to stop recommending the vaccine
Why?
• Centers for Disease Control and Prevention (CDC) advisory committee
received an overwhelming amount of data
all indicating a strong
association between ( rotavirus vaccine ) and bowel obstruction among
some infants during the first one to two weeks following vaccination.
• Apparently, many infants who received the rotavirus vaccine developed
Intussception of the bowel within one to three weeks after receiving
a dose or two of the vaccine.
• The risk of intussusception was increased 19-fold in the first 3 to 7
days after vaccination and almost fourfold (3.6) in the 8 to 14 days
after vaccination (P<0.0002).
• Children who have already received the vaccine and have not had
problems do not appear to be at risk now.
• In the meantime, research on better vaccines for rotavirus
continues.
708 males
(54.76%)
1293
585 females ( 45.24%)
All were tested using enzyme linked immunosorbent
assay (ELISA).
73 males (53.68%)
Number of infected patients 136
63 females (46.32%)
5.65% males
% of infected patients 10.52
4.87% females
% of infected males =
10.31 %
% of infected females = 10.77 %
Numbers of Infected Males to Females in Different Age Groups
40
30
30
20
21
22
17
10
SEX
Count
7
6
6
7
3
0
neonates
0-28
AGE
infants
28d-1y
toddlers
1-3
preschool
3-6
4
school
6-18
male
3
adults
>18
female
Infections Among Males : Females (saudies : non
saudies)
47
sex
45
male
female
Bars show counts
19
7
Infections in( Males : Females ) in Different
Seasons
sex
27
24
15
13
10
12
12
10
male
female
Bars show counts
Duration of Illness
80
76
60
40
20
22
Std. Dev = 1.77
0
4
0.0
2.0
4.0
7
7
6.0
8.0
DURATION (days)
Mean = 3.3
N = 118.00
10.0
Number of Patients in Different Seasons (Males : Females )
30
27
24
20
15
12
10
12
10
13
10
Count
SEX
male
0
female
winter
SEASON
spring
summer
automn
Number of Patients in Different Seasons (Males : Females )
30
27
24
20
15
12
10
12
10
13
10
Count
SEX
male
0
female
winter
SEASON
spring
summer
automn
male
SEX
10
IG
RD
U
D
N
I
IA
N
A
D
SO L
A
M N
S O TA
S
KI
P A INO
IP
IL
PH O N
TI
YP
EG A N
RI
YT
ER
I
M
YE
N N
IA
D N
I N S TI
LA
PA A N
I
ER
N
JO
SA
ALL NATIONALITIES
female
0
Count
Number of Infected Males & Females in Each Nationality
50
40
30
20
Infections Among Different Nationalities in Each Season
40
30
SEASON
20
winter
spring
summer
IG
N
I
IA
D
N
A
D
SO L
A
M AN
SO ST
KI O
P A IN
IP
IL
P H IO N
T
YP
E G IA N
R
YT
ER
I
M
YE
N N
IA
D IN
IN S T
LA N
P A IA
ER
N
U
RD
SA
0
JO
Count
10
ALL NATIONALITIES
automn
Distribution of Different Durations of Illness
80
76
60
40
20
22
Std. Dev = 1.77
0
4
0.0
2.0
4.0
7
7
6.0
8.0
DURATION (days)
Mean = 3.3
N = 118.00
10.0