Entero-Rota virus presentation available

Microbiology

1. Lecture 5
RNA-containing viruses –
causative agents of human
enteric infections:
Enteroviruses and
Rotaviruses

4. The Family Reoviridae
The family comprise of diverse
collection of viruses, that infect man,
mammals, birds.
Out of 9 genera, 4 infect man:
-Orthoreovirus (3 types);
-Orbivirus and Coltivirus
(multiple serotypes); and
-Rotavirus –seven
groups ( A-G) and
multiple serotypes within
group A.

5. The Genus Rotavirus
Type:
Rotavirus A-vast majority of human GIT infections (mainly
children)
Main:
Rotavirus B-outbreaks of gastro-enteritis in adults (China,
India, Bangladesh)
Rotavirus C-occasional episodes of gastro-enteritis in
children;
Rotavirus D
Rotavirus E
Rotavirus F
Rotavirus G
Not associated with human diseases

6. Global Estimates of Rotavirus Mortality
in Children <5 Years of Age
Each year, rotavirus causes:
•111 million episodes of gastroenteritis requiring only
home care,
•25 million clinic visits,
•2 million hospitalizations, and
•592,000 deaths.
By age 5, nearly every child will have an episode of
rotavirus gastroenteritis, 1 in 5 will visit a clinic, 1 in 60
will be hospitalized, and
1 in 293 will die. Children in the poorest countries
account for 82% of rotavirus deaths.

9. 6

10. Rotaviruses
Rotaviruses are the single most important
cause of severe diarrheal illness in infants
and young children in both developed and
developing countries worldwide.
Although diarrheal diseases are one of
the most common illnesses in this age
group throughout the world, they assume
a special significance in developing
countries, where they constitute a major
cause of mortality among the young.
The term rotavirus is derived from the
Latin word rota, which means wheel, and
it was suggested because the sharply
defined circular outline of the outer capsid
gives the appearance of the rim of a
wheel.

12. Morphology and Structure of Rotavirus (Rota -
from Latin, “wheel”)
Non enveloped,
icosahedral,
virion with a triple
–layered capsid
structure, about
80 nm in
diameter.
The RNA genome
consists of 11
segments of
double-stranded
RNA.
The double-shelled capsid
surrounds a core

14. Segmented lineardsRNA genome
Contains 11 segments coding for 12 proteins.
Genome total size is 18,550 bp. The viral mRNAs
contain 5’-methylated cap structures but lack polyA
tail. Instead, rotavirus mRNAs have at their 3’ end
a consensus sequence (UGACC) that is conserved
in all 11 viral genes.
Co-infection of cells
with different rotavirus
strains belonging to
the same serogroup
A, B or C undergo
mixing of the genome
segments (genetic
reassortment).

15. The Genus Rotavirus
The outermost viral layer contains the
structural viral proteins VP7 and VP4, which
elicit the production of neutralizing antibodies
in the host and are considered important for
protective immunity. In humans, at least 11
different VP7 antigens (G-types) and 11
different VP4 antigen (P-types) have been
identified. As the combination of G-and P-
types can vary indpendently, a binomial typing
system is used to identify strains.

18. Morphology and Structure of Rotavirus (Rota -
from Latin, “wheel”)
The double-shelled capsid
surrounds a core

20. Rotavirus
replication
-Virus attaches to
integrin or other sialic
acid host receptors
(PoRV) by the
viralVP4protein;
-Enter by endocytosis;
-Particles are partially
uncoated (The dsRNA
genome is never
completely uncoated, to
prevent activation of
antiviral state by the cell
in response of dsRNA)
in endolysosomes (loss
of theVP4-VP7
outermost layer); and
penetrate into the
cytoplasm;

21. Rotavirus
replication
The viral
polymeraseVP1synthe-
sizes a capped mRNA
occurs inside these now
double-layered particles
(DLPs) from each
dsRNA segment. This
capped mRNA is
translocated to the cell
cytoplasm where it is
translated.
Progeny cores with
replicase activity are
produced in
facctoriescalled
viroplasm.

22. Rotavirus
replication
-Complementary (-RNA)
and initial steps of viral
morphogenesis occurs;
-Late transcription occurs
in these progeny cores.
-At the periphery of virus
factories, these core are
coated withVP6, forming
immature DLPs that bud
across the membrane of
the endoplasmic
reticulum, acquiring a
transient lipid membrane
which is modified with the
ER resident viral
glycoproteinsNSP4,VP7,
andVP4;

23. Rotavirus
replication
As the particles move
towards plasma
membraine, the
transient lipid
membrane and the
nonstructural
proteinNSP4are lost,
while the virus surface
proteinsVP4andVP7
rearrange to form the
outermost virus protein
layer, yielding mature
infectious triple-layered
particles.
Mature virions are
released following cell
death.

24. Pathogenesis
Transmission is primarily by the faecal–oral route, directly
from person to person, or indirectly via contaminated
fomites. A respiratory mode of transmission has also been
proposed.

25. Pathogenesis
At least three factors play a role in the
pathogenesis of rotavirus-induced diarrhea:
-loss of brush border enzymes (inability in babies
to ferment milk lactose),
-the direct effect of the rotavirus enterotoxin
NSP4, and
-activation of the enteric nervous system.

27. The initial cell is infected by luminal virus, with the release of virus and viral
proteins (NSP4). Intracellular NSP4 also induces release of Ca
2+
from the
internal stores. A cell is secondarily infected after virus release from the initial
cell. NSP4 produced by the infection disrupts the tight junctions, allowing
paracellular flow of water and electrolytes .

28. NSP4 binds to a specific receptor on a cell and triggers a signaling cascade
,that results in release of Ca
2+
and an increase in [Ca
2+
]
I, thatacts to disrupt
the microvillar cytoskeleton. It can stimulate the EntNS to increase in [Ca
2+
]
iand
induces Cl
−
secretion.

30. Diagnosis
Specificdiagnosis of
infection
withrotavirus Ais
made by finding the
virus in the
child'sstoolby
ELISa.
A Rapid Immunoassay for the
Detection of Rotavirus Antigen in
Human Stool Specimens.
The ImmunoCardSTAT!®
Rotavirus Immunoassay is a rapidin
vitroqualitative procedure for the
detection of rotavirus antigen in
human stool. The test can be used to
aid in the diagnosis of rotavirus
associated gastroenteritis.

32. Newborn baby
Rotaviruses
vaccine
immunization
Rotavirus is a virus that causes diarrhea, mostly in babies and
young children. The diarrhea can be severe, and lead to
dehydration. Vomiting and fever are also common in babies with
rotavirus.
Two rotavirus live attenuated vaccines are currently licensed for
use in infants in the United States:
RotaTeq® (RV5-pentavalent) is given in 3 doses at ages 2 months,
4 months, and 6 months
Rotarix® (RV1) is given in 2 doses at ages 2 months and 4 months

33. Prevention
-Rotarix is a live attenuated
rotavirus serotypeG1 P1A.
-RotaTeq is a bovine
(WC3)-human reassortant
vaccine composed of five
strains, each containing a
human rotavirus gene
encoding theVP7. The
vaccine is given as 2 doses, 4
weeks apart. at 8 weeks, and
the second dose at 12 weeks.
Both rotavirus vaccines are
given orally. The vaccines
are very effective (85% to
98%) in preventing severe
rotavirus disease in infants.

35. The Family Picornaviridae
The picornaviruses cause a wide range
of infections, that may be asymptomatic or
may cause clinical syndromes, such
as:aseptic meningitides (the most common
acute viral disease of the CNS),encephalitis,
the common cold, febrile rash illnesses,
conjunctivitis, herpangina, myositis,
myocarditis, and hepatitis.
There is a possible link between
enterovirus infections and the onset of
insulin-dependent (type1) diabetes mellitus.

37. The Family Picornaviridae
small, non-enveloped, positive-strand RNA
viruses

38. Enteroviruses
Basing on the physical structure of the viruses, the
tissue cultures in which they would grow, and their
pathogenesis in humans and experimental animals,
the enteroviruses were originally classified into four
groups:
-Polioviruses (3 serotypes)-affinity for nervous tissues,
narrow host range;
-coxsackie A (24) -cause paralysis in suckling mice,
-coxsackie B (6) –cause spastic paralysis, and
-Echoviruses (33) –most do not affect lab animals,
antigenic variations are known for some serotypes.

39. Enteroviruses
Another useful way to group enteroviruses is
by the receptors that are used.
All the coxsackieviruses group B use the
"coxsackievirus and adenovirus receptor"
(CAR), but some of the echoviruses use
integrinmolecules.
To some extent, the receptor used affects
disease as it dictates, where in the body the
virus can go.

40. Enteroviruses
Today, they are
classified based on
the virus genomic
structure.
The enterovirus
genus has five
species of human
enteroviruses:
-poliovirus and
-human
enteroviruses A, B,
C, and D.

41. Enteroviruses
Virus serotypes use
their original
name given
before the current
reclassification.
Viruses within a
species can
recombine to
produce viable
hybrids.

42. Morphology and Structure
Non-enveloped, spherical, with icosaehedral
symmetry, about 30 nm in diameter,the
nakedRNAgenome.

43. The enterovirus
capsid consists of
60 capsomers that
each contain four
structural proteins
(VP1 to VP4).
The enterovirus
genome (~7,400
bases) is single-
stranded, linear,
positive RNA, with a
5′-end covalently
linked to VPg
protein.

44. Enteroviruses
replication
The translated region
of the genome
encodes a
polyprotein, which
produces four
structural proteins
and seven
nonstructural
proteins when self
cleaved.

45. The viral particle binds a
specific receptor (1) and
triggers its own
endocytosis (2). The
particle is transported by
endocytic vesicles (3) to
the Golgi apparatus (4),
and then through the
SER (5) and RER (6).
Uncoating occurs and
viral RNA is translated
into a viral polyprotein
autocleaved into
structural and
nonstructural
proteins(7).
Enteroviruses
replication

46. In replication vesicles,
positively and
negatively stranded
viral RNAs are
produced with the help
of nonstructural
proteins (8, 9). Viral
RNA encapsidates with
structural proteins (10)
and new viral particles
are relized by cell lysis
(11).

47. Pathogenesis of Enteroviruses

49. Pathogenesis of Poliovirus
The cell receptor for all three
poliovirus serotypes is
CD155, a glycoprotein that is
a member of the
immunoglobulin superfamily
of proteins.
CD155 is composed of three
extracellular immunoglobulin-
like domains: a membrane-
distal V-type domain that
binds poliovirus, followed by
two C2-type domains.

50. Pathogenesis
of Poliovirus
Ingested virus initially
replicates in the
oropharyngeal and
intestinal mucosa. Virus
replication at these
sites reaches the blood
through the lymph
nodes, resulting in a
primary viremia.
Invasion of virus into
the central nervous
system may occur
either directly from the
blood (BBB), or by
retrograde axonal
transport when virus
enters the
neuromuscular junction.

51. Pathogenesis of Poliovirus
It is believed that invasion of
the brain or spinal cord must be
preceded by viral multiplication
in extraneural tissues, which
leads to a sustained viremia.
These extraneural tissues may
include skeletal muscle and
brown fat. Virus is spread most
frequently by the fecal–oral
route. Shedding of virus from
the nasopharynx may lead to
transmission of infection by the
respiratory route, which occurs
in developed countries with
high standards of sanitation.

52. Clinical features of poliomyelitis
Most patients (95%) with poliomyelitis virus infections are asymptomatic or have
only mild systemic symptoms, such as pharyngitis or gastroenteritis. These
cases are referred to as minor illness or abortive poliomyelitis. The mild
symptoms are related to viremia and immune response against dissemination of
the virus.
Only 5% of patients exhibit different severities of nervous system involvement
from nonparalytic poliomyelitis to the most severe form of paralytic poliomyelitis.
Nonparalytic poliomyelitis.
The prodromal symptoms include generalized, nonthrobbing headache; fever of
38-40 º C; sore throat; anorexia; nausea; vomiting; and muscle aches. These
symptoms may or may not subside in 1-2 weeks.
Headache and fever, as well as signs and symptoms of nervous system
involvement (eg, irritability, restlessness, apprehensiveness, emotional
instability, stiffness of the neck and back).

53. Clinical features of poliomyelitis
Paralytic poliomyelitis:
Severe muscle pain and spasms, followed by weakness,
develop. Weakness is asymmetric, with the lower limbs affected
more than upper limbs.
Paralysis remains for days or weeks before slow recovery occurs
over months or years.

55. Clinical features of poliomyelitis
•Paralytic poliomyelitis with bulbar
involvement
•When paralysis of diaphragmatic and
intercostal musculature also occurs, patients
need immediate respiratory assistance and
intensive care because of life-threatening
respiratory failure. Cranial nerve and bulbar
involvement can cause obstruction, due to
decreased respiratory drive. The loss of
vasomotor control with circulatory collapse
also contributes to high mortality.

56. History of polio
Bobby Hill, three months old, is the
youngest polio victim ever treated in an
Iron Lung at Cincinnati General Hospital.
(1954)
At its peak in 1952, more than
21,000 Americans contracted a
paralyzing form of polio, and
3,000 died from it.
Unable to breathe, patients
entered iron lungs, which made
use of negative pressure
ventilation --a continual
displacing and replacing the air
inside of the machine --to
compress and depress the
chest, simulating respiration.

57. History of polio
Franklin Delano
Roosevelt(1933-45)
In August 1921,budding
statesman Franklin Delano
Roosevelt fell ill
withpolioduring a visit to his
family’s summer retreat in
Canada. His legs remained
paralyzed and he had to use
a wheelchair for the rest of
his life (he refused to be
photographed in his
paralyzed state to avoid
rumors of weakness and
debility).
.

58. History of polio
In 1938, Roosevelt gathered
money to fund the National
Foundation for Infantile
Paralysis.The fruit of theese
efforts was Jonas Salk’s
inactivated poliovirus vaccine,
tested in 1954 on 2 million
children or “polio pioneers,” and
Sabin’s oral polio vaccine,
licensed in 1962.

60. Hepatitis A (HAV)and E (HEV)viruses
Hepatitis A virus(HAV)Hepatitis E virus(HEV)
genome is ssRNA genome is ssRNA,
family Picornaviridae,
genusHeparnavirus
family Caliciviridae
genus is unnamed
noenvelope, no envelope
The virionis
icosahedral, 27 nm
The virion is
icosahedral, 30-32 nm
The virus is heat and
acid-stable
The virus is heat-stable
Prevalence is high Prevalence is regional

61. Hepatitis A and E
HAV-infectious hepatitisHEV–epidemic hepatitis
Fecal-oral route Fecal-oral route
Incubationperiod15-50
days
Incubationperiod15-50
days
Contagious period
extendsfrombeforeto
aftersymptoms
Contagious period
extends from before to
after symptoms
Onsetisabrupt Onset is abrupt
Mild
Vaccine is available
Normal patients, mild;
pregnant women, severe
No chronicity, no carrier
state, no oncogenesis
No chronicity, no carrier
state, no oncogenesis

62. Hepatitis A
virus(HAV) is a
picornavirus
Its capsid is more
stable than
other
picornaviruses
to acid and
other
treatments.

64. HAV: Replication

65. HAV: Replication
HAVreplicateslikeotherpicornaviruses.
ItinteractswithaHAVcellularreceptor1
(HAVCR1)toinfectcells.HAVCR1isa
class1integralmembraneglycoprotein
thatcontainstwoextracellulardomains:
avirus-bindingimmunoglobulin-like
(IgV)domainandamucin-likedomain
thatextendstheIgVfromthecell
membrane.

66. HAV: Replication
HAVisnotcytolyticandisreleasedby
exocytosis.
Thevirusreplicatesslowlywithout
producingcytopathologicaleffect(CPE).
ClinicalisolatesofHAVareverydifficultto
growincellculture.Thehumandiploid
cellsandprimatescellsareusedfor
culture.

67. Hepatitis A: Pathogenesis
(1)HAVisingestedandentersthebloodstream
throughtheoropharynxortheepithelialliningof
theintestines.
(2)ThenHAVreachesitstarget,theparenchymal
cellsoftheliver(hepatocytesandKupffer’scells).
(3)Thevirusisproducedinthesecellsandis
releasedintothebileandthenintothestool.
1 2
3

68. Hepatitis A: Pathogenesis
Crosses intestines
Blood
Bile
Stool
-An incubation period is of approximately 1 month
-HAV is shedinto the stoolapproximately 10 days
before symptomsappear
-HAV does notproduceCPE,a persistent
infectionor cancerdisease

69. Hepatitis A: Immunopathology
Natural killer(NK) cells and cytotoxic Tcells
(CTL) lyze infected cells.
Interferon, antibody, complement, and
antibody-dependent cellular cytotoxicity
are also involved in the process.
Damageto the liver results in icterus.
Icterus occurs when antibody
and cell-mediated immune
responses are detected.
Antibody protectionagainst
reinfection islifelong.

70. Hepatitis A: Epidemiology
HAVcauses40%oftheacutecasesofhepatitis.
Factors responsible for high incidence:
(1)infected individuals are contagious before
symptoms occur
(2)many (25-90%) infected people have inapparent
infection
(3)HAV is resistant to detergents, acid and T°
(4)poor hygienic conditions and overcrowding.
In developing countries, most people infected with
HAV are children. They have mild illness.
In developed countries, infection occurs later in
life.

71. Common sources of HAV
outbreaks
(1)Watersupplycanbetaintedbyrawor
improperlytreatedsewage.Thevirussurvives
formanymonthsinfreshwaterandsaltwater.
(2)Restaurant-shellfish(eg,clams,oysters,and
mussels)areimportantsourceofthevirus
becausetheyareveryefficientfilterfeedersand
canconcentratethevirionsfromcontaminated
water.
(3)Day-carecentersareamajorsourceofthe
virusspreadingamongclassmatesandtotheir
parents.

72. Hepatitis A:Clinical Syndromes
The symptoms (1) occur abruptly
15 to 50 days after exposure,
(2) intensify for 4 to 6 days before
the jaundice, icteric phase of
the disease.
Initial symptoms: fever, fatigue, nausea, loss of
appetite, and abdominal pain. Jaundice is
observed in some patients. Symptoms wane
during the jaundice period.
Immune complex-related symptoms (arthritis, rash)
rarely occur in these patients.
HAV rarely causes fatal illness.

73. Time
course
of
HAV
infection

74. HAV: Laboratory diagnosis
Serology:
-anti-HAVimmunoglobulinM(IgM)orIgG
byELISAorradioimmunoassay(RIA).
Virusisolationisnotroutinelyperformed
(efficienttissueculturesystemfor
growingthevirusisnotavailable).

75. Icteric Hepatitis
Ayellowdiscoloringof
theskin,mucous
membranes, and
eyes,causedbytoo
muchbilirubininthe
blood.
Personswithjaundice
may alsohave
nausea, vomiting,
andstomachpain
andmaypassdark
urineandpailstool.

76. Hepatitis A: Prevention & Control
HAV has no specific treatment.
Prevention:
(1)avoidanceofpotentiallycontaminatedwater
orfood
(2)properhandwashing
(3)chlorinetreatment
Control:
(1)Immuneserumglobuliniseffectivein
preventingclinicalillness
(2)Aformaldehyde-inactivated(killed)vaccine
foruseinchildrenandadultsathighriskfor
infection