Genital Herpes can be difficult to diagnose without proper tests as the symptoms may not be noticeable for some people. The visible symptoms of HSV-1 or HSV-2 may or may not be present in the infected person. Moreover, herpes symptoms may be similar to different illnesses.
The different methods of testing include diagnosis by:
- Viral Culture
- Serologic tests
- Antigen tests
Viral Culture Tests
Viral culture tests, or virology tests, are advised when there are visible symptoms of herpes. This is carried out by collecting a fluid sample, or culture from the lesions. This test involves growing the virus in specific materials known as culture medium. This is test should be taken in the initial stages of infection, preferably during the first 3 days of appearance, or else there is a higher chance of getting a false negative result.
A patient who tests positive for genital herpes with the viral culture test is most likely suffering as it does not frequently give a positive result when the cause of lesion is some other disease.
Viral culture is very specific and can also be very sensitive if the specimen is in adequate quantity. A poor sample may result in poor sensitivity as there may be very little active virus left in the lesions. The culture gives a negative report even though the patient has genital herpes.
Also viral culture does not work on older ulcerated sores, recurrent lesions, or latency as the viruses, at these stages, turn lethargic and are unable to reproduce sufficiently to produce a visible culture. The herpes viruses can reproduce in the fluid sample in 1-10 days but in case of a severe infection, this period can be shortened to 24 hours by testing technology. But this may result in reducing the accuracy of the test.
On an average, 20% of culture tests produce a false negative report on the first outbreak of genital herpes. As the recurrent outbreaks are less severe, fewer viruses are present and hence, the rate of false negative reports goes up to 50%.
Viral culture is also type-specific as it can give details whether the infection is caused by a HSV-1 or HSV-2.
Tzanck Smear Test
Tzanck smear test is an older type of viral culture test and uses scrapings from herpes lesions. The scrapings are stained and then microscopically examined in the lab. Herpes infection is indicated if specific giant cells with numerous nuclei or distinctive particles, known as inclusion bodies that carry the virus, are found in the specimen.
Though this test takes less time, is an accurate 50-70% time only. It cannot differentiate between herpes simplex and varicella (chicken pox) or the primary infection of varicella zoster virus (shingles). It is not recommended by the Centers for Disease Control as it is not reliable for providing a conclusive diagnosis of herpes infection.
Polymerase Chain Reaction (PCR) Tests
The Centers for Disease Control recommend the polymerase chain reaction tests as these are more accurate than viral cultures. PCR tests are carried out to determine the presence of genital herpes virus in spinal fluid. This test involves making many copies of the Virus’ DNA so that even small amounts of DNA in the specimen can be detected. Since PCR is highly accurate, many labs use it for herpes testing even though it is much more expensive than viral cultures.
Serologic tests or blood tests are carried out even when no symptoms of HSV-1 or HSV-2 are present. This involves testing the blood or serum for presence of any virus antibodies. These tests do not require swabbing a lesion and hence can also be done long after symptoms have faded.
When the genital herpes virus infects a person, the immune system produces certain antibodies to fight off the infection. If a blood test detects antibodies to herpes, it is evident that the person is infected with the virus, even if the virus is in a dormant state. It is also an indication that the person is a carrier of the virus and might transmit it to others.
It usually takes a time of two weeks to three months after exposure to herpes virus for the antibodies to appear in the blood. However, once antibodies are found, they remain in the body for life.
Blood tests are type-specific as they can identify antibodies that are specific to the virus and its type, HSV-1 or HSV-2. The various types of serologic tests involve newer tests like Glycoprotein gG-1 associated with HSV-1 and Glycoprotein gG-2 associated with HSV-2. Some of the other type-specific tests ELISA, Immunoblot, SureVue HSV-2 and Western Blot test.
In this type of tests, the components of the virus are specifically identified. This test is used less frequently and does not require nurturing the virus but rather seeks to diagnose genital herpes by the presence of antigens. The antigens are fragments of the virus that stimulate the immune response.
For antigen detection tests too, a swab is collected like in a viral culture test. These tests produce results more quickly are less expensive. However, better samples are needed than for culture tests as these are less sensitive. Antigen tests are not type-specific and so these tests cannot determine whether the sample is infected with HSV-1 or HSV-2.
Centers for Disease Control and Prevention. Workowski KA, Berman SM. Sexually transmitted diseases treatment guidelines, 2006. MMWR. 2006;55(RR-11):1-94.