HSV 1 or 2 Tests: Where Cross Reactions Can Cloud Decisions

Both HSV-1 and HSV-2 cause latent infections in the nervous system that last a lifetime and are incurable. Antiviral drugs can also lessen the frequency, duration, and severity of outbreaks. Over a number of years, many infected people experience less severe symptoms and fewer outbreaks, even if they are still contagious to others. 

To detect herpetic infections, a variety of laboratory tests are available. Morphologic, immunologic, serologic, virologic and molecular are the five primary categories into which they can be divided. Using a variety of laboratory methods, including Tzanck smear, HSV culture, direct immunofluorescence or PCR, physicians confirm their diagnosis. Molecular biological methods are preferred for diagnosis due to their high sensitivity, dependability, and convenience of use. In fact, when PCR is done on early lesions, it is positive in 100% of instances and positivity rates continue to be higher than 80% on later lesions for more than 30 days.

The majority of viral proteins cause a cross-reactive antibody response, which makes it difficult to distinguish between HSV-1 and HSV-2 infections using serological methods because of the high degree of genetic similarity between the two viruses. However, novel type-specific immunoassays that can distinguish between HSV-1 and HSV-2 infections have been developed after the identification of the serologically different HSV viral envelope glycoproteins gG-1 (HSV-1) and gG-2 (HSV-2). Repeat testing should be done four to six weeks after a suspected early infection in order to confirm negative results, as antibodies may take several weeks to reach detectable levels after primary infection. 

Cross-reactions between HSV 1 and HSV 2 will continue to occur, but in the interim, we should be vigilant and prepared to provide an accurate diagnosis depending on the diagnostic platform we are employing.

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