CS12 Herpes Simplex Virus_Presentation

Report
Herpes Simplex Virus
Case Study # 12
Maryna Glavatska
Michelle Chua
Background
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There are 2 types of HSV: HSV-1 and HSV-2.
Family Herpesviridae, subfamily Alphaherpesvirinae.
Baltimore classification- group I.
Large ds, linear DNA genome.
Enveloped viruses.
HSV has icosahedral nucleocapsid that contains 162
capsomeres.
• The HSV genome encodes approximately 80 proteins
and at least 10 glycoproteins.
• HSV-1 and HSV-2 establish lifelong infections, they
persist in the body by becoming latent and hiding from
the immune system in the cell bodies of neurons.
Similarities of HSV-1 and HSV-2
Similarities:
Under the electronic microscope HSV-1 and HSV-2 look identical;
Share more than 50% of their DNA;
Both infect body mucosal surfaces (usually the mouth or genitals);
Both establish latency in the nervous system;
Both types can recur
A 2-year-old child with fever for 2 days has not
been eating and has been crying often. On
examination, the physician notes that the
mucous membranes of the mouth are covered
with numerous shallow, pale ulcerations. A few
red papules and blisters are also observed
around the border of the lips. The symptoms
worsen over the next 5 days and then slowly
resolve, with complete healing after 2 weeks.
1. HSV infection was suspected. How would
the diagnosis be confirmed?
• Visual examination: multiple vesicular lesions on an
erythematous base on mucocutaneous sites that later
progress to pustular lesions, ulcers, and crusted
lesions;
• Location of lesions (anatomic site );
• Age;
• Clinical symptoms:
- Fever
- Malaise
- Inability to eat
- Irritability;
• Duration of symptoms (3-14 days).
Laboratory confirmation:
Tzanck smear- staining of scrapings
from the base of the lesions, which
demonstrates giant cells or intranuclear
inclusions.
Limitation- does not differentiate between HSV
and varicella –zoster virus infections.
Viral isolation -from vesicular fluid and
inoculation in cell culture.
Cytopathogenic effects apparent by 24
hours and include the formation of large,
round, “balloon” cells and, less commonly,
multinucleated syncytial giant cells.
Limitation-confirms Herpesviridae family.
Laboratory confirmation (cont…)
PCR- can make many copies of the virus’
DNA so that even small amounts of DNA
in the sample can be detected.
Limitation- very expensive.
ELISA – serologic test that can identify
antibodies that are specific to the virus
and its type, HSV-1 or HSV-2.
Limitation- useful only for diagnosing a
primary HSV infection, because there is no
significant rise in antibody titers in recurrent
disease
Laboratory confirmation (cont…)
Direct fluorescent antibody stain for
HSV- The fluid from blisters is
processed and stained with specific
fluorescently-labeled antibodies.
Limitations-Proper specimen collection and
transport are critical in the detection of
etiological agents. A negative result does not
rule out a viral infection and has to be
supported by PCR.
Western Blot blood test - can
distinguish between type 1 and type 2
herpes simplex antibody with
extremely high accuracy approaching
99%
2. How could you determine whether this
infection was caused by HSV-1 or HSV-2?
• Oral herpes in children commonly caused by HSV-1.
• Genital herpes can be caused by either the HSV-1 or
HSV-2 and commonly found in adolescents and adults.
• Congenital herpes simplex can be found in newborns
and is transmitted from mother to baby in utero or
during vaginal delivery. Most often caused by HSV-2.
2. How could you determine whether this
infection was caused by HSV-1 or HSV-2?
(cont…)
• There is some difference between the cytopathic effect
caused by HSV-1 and HSV-2 in the cell culture. HSV-1
produces CPE throughout the cells’ monolayer,
whereas HSV-2 CPE tend to be focal.
• Although HSV-1 and HSV-2 have many antigens in
common, the glycoprotein G (gG) antigen is unique to
each type; thus, gG1 is found only on HSV-1, and gG2 is
found only on HSV-2.
• ELISA based test can be used to detect type-specific IgG
antibodies (sensitivity around 90%).
• Western Blot
• PCR
3. What immune responses were most helpful in
resolving this infection, and when were they
activated?
INNATE
Immediate
ADAPTIVE
Late , after 96 h
IFN α, IFNβ
NK cells- kill
virally
infected cells
Dendritic cells
- produce IFN
I type
Complement
system
CD8+ T cells
-recognize viral
peptides by MHC
class I molecules on
the infected cell
surface and kill the
cell + produce IFN γ
How HSV escapes complete immune resolution?
• HSV-1 expresses an immediate-early protein, ICP 47,
that effectively blocks the MHC class I antigen
presentation pathway. ICP 47 binds with high affinity to
the human transporter associated with antigen
presentation (TAP) and blocks the binding of antigenic
peptides.
• Some HSV surface glycoproteins (gC, gE and gI) also
help the virus to escape from the immune response.
• gC binds complement C3 protein and thus depletes it
from the host's serum and inhibits complementmediated reactions.
• The virus gE and gI proteins can also bind IgG via the Fc
portion of the immunoglobulin. This coats the virus
with immunoglobulin and hides it from the immune
system.
How HSV escapes complete immune
resolution?
Why sensory neuron
remains infected?
The virus is quiescent and generates few virus
derived peptides to present on MHC class I
molecules
Neurons carry very low levels of MHC class I
molecules, which makes it harder for CD8
cytotoxic T cells to recognize infected
neurons and attack them.
4. Sites of latency
HSV-1 - usually establishes latency in the
trigeminal ganglion, a collection of nerve cells
near the ear. From there, it tends to recur on the
lower lip or face.
So, the site of latency in our patient was
trigeminal ganglion.
4. Sites of latency (cont…)
HSV-2 - usually sets up residence in the sacral
ganglion at the base of the spine. From there, it
recurs in the genital area.
4. What might promote future
recurrences?
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sunlight
wind
fever
physical injury
surgery
menstruation
suppression of the immune system
emotional stress
Oral herpes can be provoked within about 3 days of
intense dental work, particularly root canal or tooth
extraction.
5. What were the most probable means by
which the child was infected with HSV?
Oral HSV-1, is typically spread simply by the kind
of social kiss that a relative gives a child or
sharing utensils. Because children have no prior
infection with any HSV type, they have no
immune defense against the virus.
6. Which antiviral drugs are available for the
treatment of HSV infection? What are the
targets?
• Acyclovir - This is the drug of choice. Acyclovir
require the presence of a HSV-encoded
thymidine kinase in order to be converted into
its active acyclovir triphosphate form.
Acyclovir triphosphate is a potent selective
inhibitor of HSV DNA polymerase and causes
premature chain termination when it
competes with guanine triphosphate for
incorporation into newly synthesized viral
DNA. Very safe to use.
6. Which antiviral drugs are available
for the treatment of HSV infection?
What are the targets? (cont…)
• Ganciclovir, famciclovir, valacyclovir- have
similar mechanism of action; however,
ganciclovir is more toxic.
• Topical treatment- penciclovir cream or
acyclovir cream are generally not highly
effective.
• These drugs act against the replicating virus
and therefore they are ineffective against
latent virus.
Bibliography
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Murray, P., Rosental, K., Pfaller, M. Medical microbiology. Fifth
edition. 2005.
Braunwald, F., Wilson, I., Kasper, M., Longo, H. Harrison’s principles
of internal medicine. Fourteenth edition. Volume 1. 1998.
Murphy, K. Janeway’s immunobiology. Eight edition. 2012.
Slonczewski, J., Foster, J. Microbiology an evolving science. Second
edition. 2009.
Wagner, E., Hewlett, M., Bloom, D., Camerini, D. Basic virology.
Third edition. 2008.
http://pathmicro.med.sc.edu/virol/herpes.htm
http://www.herpes.com/hsv1-2.html
http://health.nytimes.com/health/guides/disease/herpessimplex/diagnosis.html
http://www.zeusscientific.com/fileadmin/media/pdfs/inserts/elisa/
infectious/R2206E.PDF

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