I antigen test, lesion smear
Herpes virus simplex virus I
Antigen, from lesion smear
This is a DFA type of test (direct fluorescent antibody) for
HSV I antigen (Ag). HSV I is a DNA virus of the herpes group.
This HSV I virus is closely related to HSV II, the "genital
herpes" virus. Both produce painful blisters and ulcerations,
and the virus can be dormant in the location and erupt and re-erupt
with sores. Since about 1990, there are antiviral agents which
may cure an initial infection if caught and treated very early;
cures are less likely once established, though treatment make help
decrease the severity. Since oral sex has become so prevalent in
modern times, the differentiation between an infection with HSV
I and HSV II is less reliable for purposes of blaming an etiology.
That is, a person could engage in oral sex with one partner and
acquire HSV II from that infected partner. The person may or may
not have an obvious sore to indicate having caught the disease;
then, through kissing only, that person may pass the HSV II on
to another person who has not engaged in any sort of genital sex.
That is, it is possible for a righteous virgin to get HSV II of
the lips or mouth.
In testing, there can be serious test cross-reactions in
serological tests, but that is not a problem between HSV I & II in the direct antigen test.
An air-dried Pap smear of the cervix or vagina, or air-dried
smear or scrape or touch prep of vulvar, penile, oral, or cutaneous
lesions can be tested. A reagent antibody against HSV I Ag is layered
onto the slide followed by a fluorescing reagent which attaches
to any HSV I Ag-Ab complexes. These are viewed under a fluorescent
microscope, and appropriately shaped fluorescent targets are indicative
of a positive test. The virus is located in epithelial cells; so,
it is of great importance that any test sample include (often requiring
scraping) those cells and not pus and salve and ulcer crust (the
greatest likelihood of an optimal sample is when dealing with a
blister/vessicular lesion). A Tzank prep smear can be prepared
exactly similarly as a duplicate sample in order to obtain faster
priliminary results.The "positive" DFA test is to be overstained by Wright's or Pap staining and the positivity correlated with viropathic epithelial cells. If there is DFA "positivity" but smear is devoid of viropathic cells, it is a situation of "indeterminate positive staining for HSV__". A blood sample for possible HSV
I serological testing (as another line of evidence to evaluate along with any DFA and/or Tzank findings)
can be drawn at the same time and serum removed and reserved for
possible further testing. But, remember that a small primary lesion may fail to generate a detectible primary antibody response! Also see HSV II.
Negative test status:
- unsatisfactory sample (the single greatest source of "false
negatives") in an HSV I lesion in an infected person...the
lab may indicate this with a message such as "acellular
smear" and may suggest this possibility with a message such
as "minimal cellular material present"..."indeterminate due to scant cellularity".
- sample from a virus-particle-poor stage in an HSV I lesion
in an infected person (a rare reason for a "false negative").
- some other type of herpes-like lesion in a person who does
not have HSV I [HERE].
DFA and morphologically positive test
HSV I infection with detection of infected cells.
- false positive (no particular reason...all tests have at least an extremely low false positive rate & no test is free of this defect)...guard against this by overstaining the DFA prep as a Tzank prep to make sure that the "positivity" is cyto-morpho-specific.
Other names for this exact or approximate agent are:
(about 2000; latest update 22 April 2008)
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