Michelle Anne Chua
Maryna Glavatska
MICR 401, Dr. Lee
Fall 2012
Group #12: Case Study and Questions: Herpes Simplex Virus
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. The physician suspects that this is an HSV infection. How would the diagnosis be
confirmed?
To confirm the diagnosis of an HSV infection in the patient, a variety of tests and
observations can be done. Based on visual examination, a physician can determine that
the patient has an HSV infection if multiple vesicular lesions on an erythematous base on
mucocutaneous sites that later progress to pustular lesions, ulcers and crusted lesions, the
location of the lesions and the age of the patient. Upon examination in our patient, the
mucous membranes of the mouth are covered with numerous shallow, pale ulcerations
and a few red papules and blisters are also observed around the border of their lips.
Clinical symptoms presented in our patient that indicate a possible HSV infection are: the
patient has a fever, inability to eat and is irritable. The typical duration of an HSV
infection ranges from 3-14 days and the patient experienced complete healing after two
weeks or 14 days.
There are several laboratory diagnostic tests and methods that can be administered to
confirm the diagnosis of an HSV, ranging from general identification of the family of
viruses the sample collected is from to the specific strain of HSV. Tznack smear, the
staining of scrapings from the base of the lesions, demonstrates giant cells and/or
intranuclear inclusions specific to the Herpesviridae family. The limitation of this
method is that it does not differentiate between HSV and varicella – zoster virus
infections, a subfamily of Herpesviridae. Another method is viral isolation from the
vesicular fluid and inoculation in cell culture. Cytopathogenic effects are apparent by 24
hours and include the formation of round, “balloon” cells, and less commonly,
multinucleated syncytial giant cells, characteristic of the Herpesviridae family. The
limitation for this method is that it only confirms that the virus belongs to the
Herpesviridae family. Polymerase chain reaction (PCR) makes many copies of the
virus’ DNA so that even small amounts of DNA in the sample can be detected, but has
the limitation of being very expensive. Enzyme-linked immunosorbent assay, also
known as ELISA, is a serological test that can identify antibodies that are specific to the
virus and differentiate between HSV-1 and HSV-2. The limitation for this test is that it is
only useful for diagnosing a primary HSV infection because there is no significant rise in
antibody titers in recurrent infections. Direct fluorescent antibody stain for HSV uses the
fluid from the blisters and stain it with specific fluorescently labeled antibodies. The
limitations for this method are that proper specimen collection and transport, critical in
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the detection of etiological agents. A negative result does not rule out viral infection and
has to be confirmed using PCR. The last diagnostic test that can be used to confirm an
HSV infection is Western Blot blood test which can distinguish between type 1 and type
2 herpes simplex antibody with extremely high accuracy of about 99%.
2. How could you determine whether this infection was caused by HSV-1 or HSV-2?
Considering the age of the patient, the location of the ulcerations, papules and blisters,
and the clinical syndromes presented, the infection is caused by HSV-1. HSV-1
infections are usually associated with infections above the waist. To differentiate
between HSV-1 and HSV-2, HSV type-specific probes, specific DNA primers for PCR
and antibodies, are used. The distinction between HSV-1 and HSV-2 and different
strains of either virus can also be made by restriction endonuclease cleavage patterns of
the viral DNA. The cytopathic effect (CPE) caused by HSV-1 and HSV-2 present
differences and can be seen in cell culture. HSV-1 produces CPE throughout the cells’
monolayer and 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; gG1 is only
found on HSV-1 and gG2 is only found on HSV-2. ELISA based tests can be used to to
detect type-specific IgG antibodies with a sensitivity of around 90%. Western blot and
PCR can also be used to differentiate whether the infection was caused by HSV-1 or
HSV-2.
3. What immune responses were most helpful in resolving this infection, and when were
they activated?
In a primary infection, interferon and natural killer cells serve important roles in limiting
the progression of the infection. Interferon activates the natural killer cells, which
recognize HSV-infected targets and lyse the cells. Macrophages phagocytize viral
antigens and present them to CD4 helper T cells and B cells to activate antigen-specific
immunity. Mononuclear cells travel to the site of infection and infiltrate the infected
tissue. Delayed hypersensitivity and cytotoxic T killer responses assist the natural killer
cell and activated macrophages in killing the infected cells. In addition to assisting in the
resolution of the infection, immunopathologic changes caused by the cellular immune
and inflammatory responses can exacerbate the symptoms.
Both the innate (immediate) and adaptive (late, after 96 hours) arms of the immune
response are involved. The humoral arm of the response, usually antibodies against
surface glycoproteins, leads to neutralization. However, the virus can escape the immune
system by coating itself with IgG via the Fc receptors and complement receptors. The
virus can also spread from one cell to another without entering the extracellular space and
coming in contact with humoral antibodies. This means that the cell-mediated responses
are vital in controlling herpes infections. The adaptive immune response is important in
disease progression, latency and control of virus spread. CD8+T cells recognize viral
peptides by MHC class I molecules on the infected cell surface and kill the cell and play
an important role in the production of IFN (interferon) γ. IFN γ controls the spread of the
virus, keeping it localized.
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4. HSV escapes complete immune resolution by causing latent and recurrent infections.
What was the site of latency in this child and what might promote future recurrences?
The site of latency in the patient is the trigeminal ganglion. HSV-1 infections usually
establish latency in the trigeminal ganglion, a collection of nerve cells near the ear.
Recurrent infections tend to be seen on the lower lip or face. HSV-2 infections tend to
reside in the sacral ganglia at the base of the spine where it recurs in the genital area.
Recurrent infections are usually caused by the reactivation of the virus despite the
presence of an antibody. The trigger is usually stress, which may have a dual effect: 1)
promote the replication of the virus in the nerve and 2) to depress cell-mediated immunity
transiently. Other triggers that might promote future recurrences include sunlight, fever,
wind, cold, physical injury, upset stomach, surgery, menstruation, suppression of the
immune system and emotional stress. Oral herpes can also be provoked within 3 days of
intense dental work, particularly root canal or tooth extraction.
5. What were the most probably means by which the child was infected with HSV?
The probably means by which the child was infected with HSV can be due to a number
of scenarios. Since the child is fairly young, HSV-1 is typically contracted by receiving a
social kiss from a relative or by sharing of utensils. Another scenario could be being in
direct contact with a playmate that has a prior HSV infection. As long as the child is in
direct contact with others, there is a possibility of contracting HSV. Since children have
no prior infection to any HSV type, they have no immune defense against the virus.
6. Which antiviral drugs are available for treatment of HSV infection? What are the
targets? Were they indicated for this child? Why or why not?
Acyclovir (ACV) is the most effective anti-HSV drug. It targets viral DNA polymerase
after it has been phosphorylated by viral thymidine kinase to acyclovir monophosphate.
Host cell enzymes further the phosphorylation to acyclovir triphosphate and the
compound then binds viral DNA polymerase and may also be incorporated into viral
DNA, terminating synthesis. Acyclovir would be recommended for the child to use
because it is very safe to use and it is highly effective in treating HSV infections.
Other antivirals on the market are ganciclovir, famciclovir and valacyclovir, which have a
similar mechanism of action as acyclovir of inhibiting viral DNA replication, however
ganciclovir is more toxic. Valacyclovir is an analog of acyclovir and is quickly
converted to acyclovir in the tissues. Famciclovir is converted to the active antiviral
penciclovir Topical antivirals used to treat HSV infections are penciclovir cream and
acyclovir cream but neither are highly effective. The target the replicating virus so they
are ineffective against the latent virus. None are recommended for the child since
ganciclovir has a high toxicity, famciclovir and valacyclovir have to be converted to an
active form before therapeutic effects are noticeable and are usually used to treat HSV-2
infections.
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References:
1. Murray, P., Rosental, K., Pfaller, M. Medical microbiology. Fifth edition. 2005.
2. Braunwald, F., Wilson, I., Kasper, M., Longo, H. Harrison’s Principles of Internal
Medicine. Fourteenth editions. Volume 1. 1998.
3. Murphy, K. Janeway’s Immunobiology. Eigth Edition. 2012.
4. Slonczewki, J., Foster, J. Microbiology An Evolving Science. Second Edition. 2009.
5. Wagner, E., Hewlett, M., Bloom, D., Camerini, D. Basic Virology. Third Edition. 2008.
6. Hitner, H., Nagle, B. Pharmacology. Sixth Edition. 2012.
7. http://pathmicro.med.sc.edu/virol/herpes.htm
8. http://www.herpes.com/hsv1-2.html
9. http://health.nytimes.com/health/guides/disease/herpes-simplex/diagnosis.html
10. http://www.zeusscientific.com/fileadmin/media/pdfs/inserts/elisa/infectious/R2206E.PD
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