The Test Sample
What is being tested?
Herpes simplex virus testing is performed to identify an acute herpes infection or to detect herpes antibodies, an indication of a previous exposure to herpes. One of the most common viral infections, herpes simplex virus (HSV) exists as two main types, HSV-1 and HSV-2. Both types are contagious and periodically cause small fever blisters (vesicles) that break to form open lesions. HSV-1 primarily causes blisters or "cold sores" around the oral cavity and mouth, while HSV-2 usually causes lesions around the genital area; however, either one can affect the oral or genital area.
The herpes simplex virus can be passed from person to person through skin contact while the sores are open and healing and sometimes when there are no visible sores. HSV-2 is frequently a sexually transmitted disease, but HSV-1 also may be acquired during oral sex and found in the genital area. According to the American Sexual Health Association and its Herpes Resource Center, about 50% of adults in the U.S. have HSV-1 and about 17% have HSV-2. Because symptoms may be mild, however, 90% of those who have HSV-2 may be unaware that they have been infected.
When someone is first infected, the person may have obvious and painful blisters at the site of infection, which usually appear within two weeks after the virus is transmitted. The lesions generally heal within two to four weeks. The blisters can appear in the vaginal area, on the penis, around the anus, or on the buttocks or thighs. This primary episode can include a second outbreak of blisters and even flu-like symptoms such as fever and swollen glands. However, not everyone develops blisters, and sometimes symptoms are so mild that they are unnoticeable or mistaken for something else, such as insect bites or a rash.
Once someone is infected and the initial infection resolves, the person will harbor the HSV in a latent form. During periods of stress or illness, the virus may reactivate.
People with conditions that cause their immune system to be suppressed, such as those with HIV/AIDS or those who have had an organ transplant, may have more frequent and serious outbreaks of HSV. While there is no cure for herpes, antiviral medications can suppress outbreaks and shorten the duration of symptoms and active shedding of virus.
Rarely, the virus can cause neonatal herpes when a woman transmits the virus to her baby during a vaginal delivery. Neonatal herpes symptoms appear during the first month of life and, if left untreated, can cause long-term damage to a baby's health. A pregnant woman who has been diagnosed with herpes may be monitored regularly prior to delivery to identify a reactivation of her infection, which would indicate the necessity for a caesarean section to avoid infecting the baby.
The herpes simplex virus can be transmitted to the brain, causing encephalitis. This illness can be fatal or cause serious, permanent neurological problems in those who survive.
HSV testing detects the virus itself, its viral DNA, or antibodies to the virus. During an acute primary infection or reactivation, the virus may be detected by:
- Herpes culture. A sample of fluid is collected via swab from an open sore and inoculated into cells that allow the virus to grow. Once the the virus is detected, it can be further Identified as HSV-1 or HSV-2, which may be useful for prognosis. This test is sensitive and specific, but it takes two or more days to complete. False negatives can occur if there is not enough active virus in the test sample, which can occur if the lesion is cultured more than 48 hours after the symptoms appear.
- HSV DNA testing or HSV PCR. This method detects HSV genetic material in a patient's sample from the blister, blood, or other fluid, such as spinal fluid. DNA testing is usually done only if the culture is negative but the practitioner still suspects herpes, or if the patient has received treatment for herpes. This method can detect the virus as well as identify the type of herpes virus. Because this test is more sensitive than culture, it is useful in circumstances where the virus is present in low numbers (such as viral encephalitis) or if the lesion is several days old. This is the best method to detect HSV meningitis, encephalitis, or keratitis (inflammation of the cornea).
- HSV antibody testing. Antibodies to HSV are specific proteins that the body creates and releases into the bloodstream to fight the infection. HSV IgM antibody production begins several days after a primary (initial) HSV infection and may be detectable in the blood for several weeks. HSV IgG antibody production begins after HSV IgM production. Concentrations rise for several weeks, slowly decline, and then stabilize in the blood. Once someone has been infected with HSV, they will continue to produce small quantities of HSV IgG. HSV antibody testing can detect both viral types (HSV-1 and HSV-2), and tests are available that can detect the early IgM antibodies as well as the IgG antibodies that remain forever in those who have been exposed.
How is the sample collected for testing?
Your health care practitioner will take a swab or scraping from a blister or sore in the genital area. A sample of cerebrospinal fluid (CSF) may be collected from the spinal column when meningitis or encephalitis is suspected. For antibody testing, a blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.