Laboratory Studies
Culture
Herpes simplex virus (HSV) infection is best confirmed by isolation of the virus in tissue culture (the criterion standard for diagnosis). Tissue culture success is operator-dependent, but this modality can yield positive results within 48 hours of inoculation.
Characteristic cytopathic effect with ballooning of cells and cell death are observed, and death of the entire monolayer of cells may be rapid.
Immunofluorescent staining of the tissue culture cells can be used to quickly identify HSV and can distinguish between types 1 and 2.
Tzank smear
The characteristic cytologic changes induced by HSV can be demonstrated in Tzank smears (see Procedures); however, this procedure does not distinguish between HSV-1 and HSV-2.
Rapid diagnosis (usually within an hour) is possible based on the histological appearance of the lesion.
Multinucleated giant cells and epithelial cells containing eosinophilic intranuclear inclusion bodies distinguish the lesions of herpesviruses.
Punch biopsy provides more reliable material for histological examination, particularly when lesions are infected with bacteria and fungi.
Polymerase chain reaction
Detection of HSV DNA in clinical specimens is possible with polymerase chain reaction (PCR) techniques. PCR is more sensitive than culture and is the preferred test for CNS and ocular infections.
In HSV encephalitis, PCR using CSF provides a rapid, noninvasive diagnostic technique that is as sensitive as brain biopsy. [18]
PCR has been used to detect HSV-2 as the cause of recurrent meningitis (Mollaret) and has shown a strong association between HSV-1 and Bell's palsy.
PCR can be used to detect asymptomatic viral shedding.
Direct fluorescent antigen (Immunofluorescence)
Cells scraped from ulcer bases can be stained with a direct fluorescent antibody, used to distinguish HSV-1 from HSV-2. Additionally, tissue culture cells can also be stained (see above). This procedure can usually be performed within 2-3 hours. [19]
Antibody testing
Antibody testing can demonstrate a primary seroconversion, particularly with HSV-1 in childhood. [1] If serology results are negative while viral culture of specimen is positive, one can assume primary infection.
Because of sero–cross-reactivity, HSV-1 and HSV-2 are not generally distinguishable unless a glycoprotein G antibody assay is available. Testing for HSV-specific immunoglobulin M (IgM) antibodies is not available.
Antibody titer increases generally do not occur during recurrences of HSV infection. Therefore, the test is generally not used for the diagnosis of mucocutaneous HSV relapse.
Antibody testing has been the mainstay of large-scale epidemiologic studies.
Imaging Studies
Brain imaging studies in HSV encephalitis generally demonstrate focal localization in the temporal area that is associated with edema and contrast enhancement.
Procedures
Tzanck preparation
Tzanck preparation is a time-honored procedure for assisting in the diagnosis of cutaneous herpesvirus infections. However, it does not easily distinguish HSV-1, HSV-2, and varicella-zoster virus.
Typically, an intact vesicle is used from which the vesicular fluid is aspirated by puncture with a sterile tuberculin syringe. This fluid can be used for viral culture or PCR.
Aspiration should facilitate complete collapse of the vesicle because it is not multiloculated as cutaneous poxvirus infections can be.
After aspiration, the vesicle should be unroofed aseptically.
Using a sterile instrument, the floor of the newly produced ulcer can then be scraped. The obtained material can be spread on a glass microscope slide and then dried and fixed for staining.
Staining can be performed with a Papanicolaou smear stain or, alternatively, whatever is available will suffice (eg, Gram, Giemsa, or Wright stain).
A positive result is the finding of multinucleate giant cells.
Direct fluorescent antigen
Using appropriate immunofluorescent antibody reagents, the smear can be used to distinguish different herpesviruses and nonherpesviruses that may be present (eg, vaccinia, smallpox).
-
Herpes simplex virus type 1. Primary herpes can affect the lips, and the ruptured vesicles may appear as bleeding of the lips. Courtesy of A.K. ElGeneidy, DDS.
-
Herpes simplex virus type 1. Recurrent herpes is most often noted clinically as herpes labialis, with clustered vesicles (often coalescing) on the lip vermilion and often on the perioral skin. Recurrences generally occur in the same area each time, although their severity may vary. Courtesy of Sara Gordon, DDS.
-
This neonate displayed a maculopapular outbreak on his feet due to congenitally acquired herpes simplex virus infection. Courtesy of the CDC/Judith Faulk.
-
Herpes simplex virus type 1. Recurrent herpes is occasionally observed intraorally. Inside the oral cavity, recurrent herpes typically affects only keratinized tissues, such as the gingiva or the hard palate. Vesicles often break quickly, so the clinician may observe small clustered ulcers. Courtesy of Sheldon Mintz, DDS.
