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Laboratory Diagnosis of Herpes Simplex Virus Type 1

written by: Emma Lloyd•edited by: Leigh A. Zaykoski•updated: 5/26/2010

Several different test types can be used in the laboratory diagnosis of herpes simplex virus type 1. The best test to use depends on whether the patient has an active herpes infection, and how much time has elapsed since he or she was initially exposed to the virus.

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    About Herpes Simplex Virus

    There are two types of herpes simplex virus, or HSV. Herpes simplex type 1 is known as oral herpes, while herpes simplex type 2 is known as genital herpes. The two viruses are very similar in all aspects, except that each type tends to infect these different areas of the body.

    Both HS1 and HSV2 are transmitted via close contact with someone who is actively infected. Transmission can occur via sexual contact or via lower-intimacy skin-to-skin contact such as during a kiss. The initial infection causes the development of lesions on the infected area; typically the mouth in the case of HSV, and the genitals in the case of HSV2.

    After the initial infection, the virus becomes latent, which means it is still present in the body, but no longer causes a symptomatic infection. During the latent period, the virus is present in sensory nerve cells. Occasionally an active, symptomatic infection might occur, often in response to physical or mental stimuli or stress.

    The ability of HSV to become latent in sensory nerve cells means that the virus cannot be completely eradicated, therefore infection with HSV is incurable. Treatment for active infection can reduce the severity of lesions and reduce the duration of active infection. Treatment is in generally in the form of topical or oral anti-viral medications.

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    Methods for Laboratory Diagnosis of Herpes Simplex Virus Type 1

    Several different lab tests can be used in the diagnosis of HSV1. These include blood tests for HSV antibodies, and culture tests in which a patient sample is examined for the presence of live viruses.

    Laboratory diagnosis of herpes simplex virus type 1 might include one or more of the following test types.

    Viral Culture Test

    In this test, the patient gives a sample of fluid from an active HSV1 lesion. For best results the sample needs to be given in the first three days after the appearance of the lesion. If the virus is present in the fluid, it can be cultured in the laboratory under the right conditions.

    This test can take up to ten days to complete, however, which can be problematic when infection is severe. If the infection is severe enough, the test period can be shortened significantly, but results are less accurate.

    Polymerase Chain Reaction (PCR) Test

    This laboratory test is used to detect viral DNA in the fluid sample. This is useful because a PCR is highly sensitive and can detect viral DNA even when the concentration is very low. It is much faster than a viral cuilture, and produces more accurate results.

    Tzanck Smear Test

    For this test a sample of scrapings from a lesion is examined under a microscope. In this test the virus itself cannot be detected; what is detected here is signs of HSV infection in cells. This test is fairly old and is not often used, as it is much less accurate than culture or PCR tests.

    Serologic Testing

    This type of testing involves the use of assays that check a blood sample for antibodies that the body produces in response to HSV infection. If someone has been infected with the virus, their immune system generates antibodies specific to that virus. Serologic testing is particularly useful because it is a quick and relatively simple way to distinguish between HSV1 and HSV2 infection.

    The main drawback of this method of laboratory diagnosis of herpes simplex virus type 1 is that it is not effective during initial infection, because it takes time for the body to generate antibodies to the virus. The best time to carry out serologic testing is actually around three to four months after the initial infection.

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