ADENOVIRUSES: Properties ofAdenoviruses
• 80-110nm in size with icosahedral (cubic) symmetry
• dsDNA and Non enveloped
• Fibers protrude from vertex capsomers
• 12 pentons and 240 hexons
• Hexons, pentons and fibers are important antigens in
classification and diagnosis of disease
• Pentons are responsible for CPE.
• Fibers are associated with haemagglutinating activity.
2
Genome AV
• Theterminal protein (TP) is covalently attached to each
end of the genome.
5
GENOME
• Non-segmented, linear double-stranded
(ds)DNA of 35-36kb encoding about 40
proteins. The genome has terminally
redundant sequences which have
inverted terminal repetitions (ITR).
6.
Classification
• Classification ofAdenoviridae is complex.
• In humans, there are 57 accepted human
adenovirus types in seven species (Human
adenovirus A to G): (antigenic types)
– The different adenoviruses cause a wide
variety of common and sporadic infections and
there is not a strict one-to-one relationship
between the serotype and disease.
6
GENE EXPRESSION
Transcription isnuclear, in 3 phases; early, intermediate (replication), and
late (virion assembly). All genes are transcribed by host RNA pol II
REPLICATION NUCLEUS
1. Attachment of the viral fibers to the host CAR adhesion receptor. Subsequent binding of
the penton protein to host integrin entry receptors mediates internalization into the host cell
by clathrin-mediated endocytosis of the virus and fiber shedding. Some serotypes also
seem to use macro-pinocytosis.
2. Disruption of host endosomal membrane by lytic protein VI releases the viral capsid in the
cytosol.
3. Microtubular transport toward nucleus of the viral genome still protected by the core
protein VII and a partial capsid mainly composed of hexons and protein IX.
4. Import of the viral genome into host nucleus mediated by core protein VII.
5. Transcription of early genes (E genes) by host RNA pol II: these proteins optimize the
cellular milieu for viral replication, and counteract a variety of antiviral defenses.
6. Intermediate genes activate replication of the DNA genome in the nucleus.
7. Transcription of late genes (L genes) by host RNA pol II, mostly encoding structural
proteins.
8. Host translation shutoff performed by the viral 100K protein.
9. Assembly of new virions in the nucleus.
10. Virions are released by lysis of the cell.
11. Virion maturation by the viral protease.
8
9.
Virus effect oncells
• Growth of virus in tissue culture leads to acid
production due to glycolysis
• CPE are rounding, enlargement, aggregation of
cells into grape like clusters
• Some adenoviruses form intranuclear inclusions.
• Primary human embryonic kidney (HEK
HEK) cells are
the best host for the replication of the human
adenoviruses.
• Cytopathic for human cell cultures like primary
kidney and continuous epithelial cells
9
10.
Virus tropism
• Adenovirusesinfect and replicate in
epithelial cells of the respiratory tract, eye,
gastrointestinal tract, and urinary tract.
10
11.
Gene therapy
• Potentialuse of adenoviruses as gene-delivery
vehicles for gene therapy(because it is easy to
cultivate in culture)
• Delivery of foreign DNA is achieved by coupling
DNA of interest with adenovirus
• Can serve as gene delivery vehicles for cancer
therapy, gene therapy, and genetic immunization
studies.
11
12.
Adenovirus infections inhumans:
Pathogenesis:
• Adenoviruses infect and replicate in epithelial
cells of the respiratory tract, eye, GIT, urinary
bladder and also liver.
• Group – C adenoviruses persists as latent
infections for years in adenoids and tonsils and
are shed in feces for many months after initial
infection.
12
13.
Clinical findings:
• Adenoviruses1-7 are most common types worldwide and
associated with most of illnesses.
• They are responsible for 5% of acute respiratory disease
in children.
• Serotypes 3, 5 and 7: lower respiratory tract infections.
• Serotypes 4 and 7: acute respiratory disease.
• Serotypes 8, 19, and 37: epidemic keratoconjunctivitis.
• Serotypes 40 and 41: gastroenteritis.
• Serotype 14: can cause potentially fatal adenovirus
infections.
13
14.
TABLE .1 Adenovirusinfections associated with disease or persistence
Disease Individuals Most At Risk Principal
Serotypes
Acute febrile pharyngitis Infants, young children 1,3, 5,7
Pharyngoconjunctival fever School-aged children 3, 7, 14
Acute respiratory disease Military recruits 3, 4, 7, 14, 21
Pneumonia Infants, young children 1,3, 7
Pneumonia Military recruits 4, 7
Epidemic keratoconjuncti. Any age group 8, 11, 19, 37
Pertussislike syndrome Infants, young children 5
Acute hemorrhagic cystitis Young children 11, 21
Gastroenteritis Infants, young children 40, 41
Meningoencephalitis Children and immunocomp-ed hosts 7, 12, 32
Hepatitis Infants/children with liver transplants 1, 2, 5
Myocarditis Children ?
Persistence Bone marrow transplant recipients;
patients with AIDS or other
immunosuppression syndromes.
In urinary tract 34, 35
In colon 42, 49
14
Laboratory diagnosis
(Isolation andidentification of virus)
• Stool, urine, throat, conjunctiva or rectal swab
• Primary human embryonic kidney cells, HEp-2,
HeLa
• Virus growth can be identified by CPE and medium
becomes acidic
• Isolates can be identified by IF -tests, Neutralization
test, or haemagglutination test
• Adenovirus can be tested rapidly by using “shell
vial” technique. Viral specimens are centrifuged
directly onto tissue culture cells, then incubated for
1-2 days then tested with monoclonal antibodies.
• PCR, ELISA, E.M can also be employed.
17
18.
Serology
• Complement fixationtest (CFT)
• Neutralization test (Nt)
• Haemagglutination test
Epidemiology
• Adenoviruses are spread by
– fecal - oral route
– Respiratory droplets
– Fomites
Treatment
– None, supportive
18
19.
Prevention & control
•Careful hand washing is the easiest way to prevent
infections.
• Risk of water borne outbreaks of conjunctivitis can be
minimized by chlorination of swimming pools and
waste water
• Strict asepsis during eye examinations is needed for
control of epidemic keratoconjunctivitis.
• Attempts to control adenovirus infections in the military
have focused on vaccines.
• Live adenovirus vaccine containing types 4 and 7 was
introduced in 1971.
19
20.
Parvoviridae
Parvoviridae: PARVOVIRUSES
(Properties)
• Theyare simplest DNA viruses.
• are small, nonenveloped viruses with a linear, ssDNA
genome of about 5 kb size.
• The genome is replicated through rolling-hairpin
mechanism.
• small coding capacity of their genome causes to depend
on helper activity from other viruses (eg. adenovirus, or
herpesviruses) for their replication.
• The only known human pathogenic parvovirus, B19
(Erythrovirus), has a tropism for erythroid progenitor
cells.
20
21.
• Adenoassociated virus(AAV- Dependovirus
genus) is non pathogenic.
• Parvoviruses are icosahedral (cubic),
nonenveloped particles with size of 18-26nm.
• Virions contain two protein coats, and are
resistant to inactivation.
Virion Genome
21
VIRION
22.
REPLICATION NUCLEAR
1. Attachementto host receptors initiates
clathrin-mediated endocytosis of the virion into the host cell .
2. The virion penetrates into the cytoplasm via
permeabilization of host endosomal membrane .
3. Microtubular transport of the virion toward the nucleus.
4. The viral ssDNA genome penetrates into the nucleus.
5. The ssDNA is converted into dsDNA by cellular proteins.
6. dsDNA transcription gives rise to viral mRNAs when host cell enters S
phase and translated to produce viral proteins.
7. Replication occurs through rolling-hairpin mechanism, with NS1
endonuclease binding covalently to the 5' genomic end.
8. Individual ssDNA genomes are excised from replication concatemers by a
process called junction resolution.
9. These newly synthesized ssDNA can either
a) be converted to dsDNA and serve as a template for transcription
/replication
b) be encapsidated to form new virions and released by cell lysis.
22
23.
• Viral replicationcauses cell death, interrupting
red cell production.
• It is the cause of
– erythema infectiosum (“fifth disease”) which is a
common childhood exanthema,
– polyarthralgia arthritis syndrome in normal adults,
– aplastic crisis in hemolytic disorder patients,
– chronic anemia in immunocompromised patients and
fetal death.
23
Laboratory diagnosis
• Detectionof B19 IgM Ab is indicative of recent
infection.
• B19 IgG antibody persists for years.
• Viral DNA can be detected by PCR,
• dot - blot hybridization of serum or tissue extract.
• B-19 DNA can be detected in serum, blood,
tissues and respiratory secretions.
• The virus is difficult to grow.
26
27.
Epidemiology
• The B19has worldwide spread.
• Infections are transmitted via respiratory
tract.
• Infections can occur all round the year in
all age groups, as outbreaks or as
sporadic cases.
27
28.
Treatment:
• There isno antiviral drugs.
• Fifth disease and transient aplastic crisis are
treated symptomatically.
• Immunoglobulin preparations with neutralizing
antibodies can be used to cure persistent B19
infections in immuno-compromised patients.
TRANSMISSION
• Respiratory, oral droplets.
28
29.
Prevention & control
•There is no vaccine against human parvovirus.
• Standard infection control practices should be
followed to prevent transmission of this virus to
health care workers from patients with aplastic
crisis, etc.
29
30.
PAPOVAVIRUSES…………. Older name
Classification
•The Papovaviruses Family is formally split the
two viruses into their own families,
Polyomaviridae
Polyomaviridae and Papillomaviridae
Papillomaviridae .
• However, the family name is more indicative of
the history of the virus, than of its component
subsets. Papova is derived from the letters:
– PApilloma virus
– POlyoma virus
– VAcuolating virus
30
31.
POLYOMAVIRIDAE
Classification
• Members ofthe genus Polyomavirus share physical and
biological characteristics that place them into separate family.
• Polyomaviruses are 40 to 45 nm particles consisting of 3 capsid
proteins; a ds-, covalently closed circular DNA genome
• Nonenveloped capsid with cubic (icosahedral) symmetry DNA
viruses that replicate in the nucleus of squamous epithelial
cells.
• multiply most efficiently in cells of their host, resulting in a lytic
cell death.
• In other host cells, many of the viruses do not multiply,
producing only the early gene products that may result in a
transforming or oncogenic infection.
31
32.
Classification …cont’d
• Family:Polyomaviridae
• Genus:
• Alphapolyomavirus
• Betapolyomavirus
• Deltapolyomavirus
• Gammapolyomavirus
• GENOME
– It is about 5 kb in size, associated with cellular histones in a
chromatin-like complex. Encodes for 5-9 proteins.
– On rare non-specific recombination, the viral genome can be
integrated in host chromosome. This inactivates the integrated virus
but can give the host cell a replicative advantage sometimes leading
to malignant tumours.
32
33.
REPLICATION NUCLEAR
1. Attachementof the viral proteins to host receptors triggers
endocytosis of the virus into the host cell.
2. Virion transits through endoplasmic reticulum where host
protein rearrange its capsid structure
3. Loss of VP1 in the low-calcium conditions of the cytosol
4. Import of genomic DNA into host nucleus.
5. Transcription of early genes (LT and sT genes)
6. Replication of the DNA genome in the nucleus.
7. Transcription of late genes encoding for structural proteins
(VP1, VP2 and VP3).
8. Assembly of new virions in nuclear viral factories.
9. Virions are released by lysis of the cell.
33
34.
Polyomaviruses
• Polyomaviruses areimportant model tumor viruses.
• SV40 from monkeys, BK virus and JC virus from
humans are polyomaviruses causing tumors.
• SV40 contaminated early lots of live and killed
poliovirus vaccines that had been grown in monkey
cells unknowingly infected with SV40.
• Millions of people worldwide received such SV40
contaminated vaccines between 1955 and 1963.
• Recently SV40 DNA has been detected in several
types of human tumors like brain tumors,
mesotheliomas (lung) and bone tumors.
34
35.
Polyomaviruses of human
HumanBK virus
(BKV)
Common infection of childhood;
persists in kidney epithelium and
possibly lymphocytes
JC virus
(JCV)
Common infection of childhood;
persists in kidney epithelium,
lymphocytes, and bone marrow;
produces Progressive multifocal
leukoencephalopathy (PMLE) in
immuno-compromised hosts
35
36.
• The humanpolyomaviruses (BK and JC) have been
isolated from immuno-compromised pts.
• BK virus causes cystitis, nephropathy and severe renal
allograft dysfunction
• JC virus is the cause of progressive multifocal
encephalopathy, a fatal disease in immune compromised
persons.
• The two viruses are antigenically distinct but induce tumor
antigen.
• Both viruses may persist in kidneys of healthy persons
after primary infection and can be reactivated after
immunity is impaired.
• Currently, no effective antiviral agents are available to treat
these opportunistic infections.
36
37.
Papillomaviruses: from Papillomaviridae
Papillomaviridae
•Papillomaviruses are slightly larger with larger genome
and more important to human disease than
polyomaviruses .
• The PV particles are 52 -55 nm in diameter.
• There are more than 100 distinct human papillomavirus
(HPV) types have been recovered.
• The virion particles consist of a single molecule of ds
circular DNA ≈8,000 bp in size, and nonenveloped,
icosahedral .
• These viruses are difficult to grow in vitro.
• The virus has high tropic for epithelial cells of the skin
and mucous membranes.
37
GENOME
• Circular dsDNA,about 8 kb in size, associated with
cellular histones in a chromatin-like complex.
• On rare non-specific recombination, the viral genome can
be integrated in host chromosome. This inactivates the
integrated virus but can gives the host cell a replicative
advantage sometimes leading to malignant tumours.
GENE EXPRESSION
• Only one strand of the genome is transcribed and yield
two classes of proteins expressed by alternative splicing :
40
A. Early Proteins: non-structural regulatory
proteins (E1-E7).
B. Late Proteins: the structural proteins L1
and L2. E7 can be expressed from
the E6 mRNA.
41.
REPLICATION NUCLEAR
1. Replicationis divided in two distinct steps that are linked to the
differentiation state of the host epithelial cell:
a) The plasmid replication takes place in the basal squamous epithelial
cells. It corresponds to viral DNA replication in synchrony with the host
cell chromosome in order to ensures an average of one viral genome
per basal cell.
1. Attachment of the viral proteins to host receptors mediates endocytosis into vesicles
in the basal squamous epithelial cell.
2. Transport to the nucleus and uncoating of the viral DNA.
3. Early-region transcription and translation of the early proteins.
4. Steady-state viral DNA nuclear replication. Requires the origin of DNA replication in
cis and the viral E1 and E2 proteins in trans.
b) The vegetative replication, which occurs in differentiated keratinocytes.
In these cells, which no longer undergo cellular DNA synthesis, there is
a burst of viral DNA synthesis with active production of virions.
1. Vegetative viral DNA synthesis.
2. Transcription of the late region.
3. Capsid proteins L1 and L2 synthesis.
4. Nuclear capsid assembly and release of viruses.
41
42.
• Viral nucleicacid can be found in basal stem
cells, but capsid proteins are present in
uppermost layer of differentiated keratinocytes.
• The HPV capsid consists of two structural
proteins. The major capsid protein (L1)
represents ≈80% of the total viral protein. A
minor protein (L2) are virally encoded.
• HPV – causes warts (papilloma) like skin warts,
plantar warts, flat warts, malignant tumours,
genital condylomas and laryngeal papillomas.
42
43.
• TRANSMISSION Sexual,indirect and direct contact, auto-
inoculation (scratching).
• HPV is associated with genital lesions , Cervical cancer;
Anogenital cancer and genital warts.
– HPV 16, 18, 31, 45 are mostly found.
– Types 16 and 18 are at high risk of causing cancer.
– Types 6 and 11 are classified at low risk.
• Many HPV types are considered benign.
• Warts tend to disappear spontaneously with time (but not
in immunoccompromised patients).
43
Laboratory diagnosis
• Serologicmethods (ELISA), Viral DNA can be
detected by PCR
Treatment:
• Phenol therapy on wart, Cryotherapy
• cervical dysplasia for surgical, via loop
electrosurgical excision repair, or by laser.
• Cervical cancer is treated by surgery,
radiotherapy, and chemotherapy, with early stage
tumors having a better prognosis than more
advanced tumors.
49
50.
Prevention
• Interruption ofTransmission
• Pap smear screening can prevent most cervical
cancers (the most serious consequence of HPV
infection).
• To decrease sexual promiscuity.
• condom use may reduce the incidence of genital HPV
infection (Although HPV can infect genital areas that
are not covered by condoms)
• Vaccines is going to be most cost-effective (to young
adolescents who are not yet sexually active and Even
in sexually active individuals).
• Vaccine against HPV types 6, 11, 16 and 18.
50
Editor's Notes
#15 Adenoviruses (B group)—particularly types 3, 7, and 21—are thought to be responsible for about 10–20% of pneumonias in childhood.
#20 Linear, ssDNA genome of about 4 to 6 kb in size.
#31 =POLYOMA VIRUSES
Table 61.1 lis
These viruses demonstrate a restricted cellular host range in nature that is reflected in cell cultures as well. Its the members of the family Polyomaviridae, genus Polyomavirus (1).
#37 Papillomaviruses are small, nonenveloped, icosahedral DNA viruses that replicate in the nucleus of squamous epithelial cells. The PV particles have a sedimentation coefficient (S20,W) of 300. The PV particles are 52 to 55 nanometers in diameter
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