Herpes Simplex Virus - HSV

Herpes simplex virus (HSV) is a prevalent, easily transmissible virus that causes lifelong viral infection. There are two known subtypes: HSV-1 and HSV-2. HSV-1 can cause both oral and genital infections, but HSV-2 is the major cause of genital herpes. Classically, infections result in painful oral or genital lesions; however, symptoms are often mild or not present at all, which makes diagnosis difficult. After primary infection, HSV becomes latent in nerve roots and can reactivate, resulting in symptom recurrence and viral shedding.  Neonates can be infected via vertical transmission from an infected mother during pregnancy, delivery, or during the postpartum period.  HSV is also a rare but serious cause of encephalitis that can affect patients of all age groups.  The recommended test for active genital herpes is viral culture or polymerase chain reaction (PCR) testing of vesicle fluid.    PCR is the recommended testing method for neonates and in cases suspected of encephalitis or bloodborne infection.    Serologic testing is performed to identify past or recent exposure to the virus but cannot determine the exact timing of exposure or the site of infection. Subtyping can be performed by PCR or serologic testing; however, the results do not usually change clinical management.  

Quick Answers for Clinicians

Which laboratory tests are used to confirm herpes simplex virus infection?

Virologic and serologic testing methods are available to confirm herpes simplex virus (HSV) infection. Direct detection of the virus by polymerase chain reaction (PCR) or viral culture is recommended for neonates and patients with active infection with lesions, to test for disseminated bloodborne infection in immunocompromised patients, and for cerebrospinal fluid (CSF) testing. Serologic testing for immunoglobulin G (IgG) can be used to determine if a person has ever been exposed to HSV but cannot determine exactly when the exposure occurred or the site of infection. Type-specific serologic testing for HSV-1- and HSV-2-specific glycoproteins can determine the subtype of the virus, which may be useful for epidemiologic studies and patient counseling, but generally lacks clinical significance.  

What is the significance of type-specific herpes simplex virus testing?

Subtyping herpes simplex virus (HSV) using polymerase chain reaction (PCR) or serology testing can provide epidemiologic information about transmission of the virus and potentially guide patient counseling regarding disease acquisition, but the results are generally clinically insignificant because treatment is the same for HSV-1 and HSV-2. 

When should patients be tested for herpes simplex virus infection?

If a patient has active lesion(s), polymerase chain reaction (PCR) testing for herpes simplex virus (HSV) should be performed on a lesional sample. Serology testing is used in the absence of active lesions. It can take days to weeks following initial exposure for immunoglobulin G (IgG) antibodies to develop and up to 6 months for HSV type-specific antibodies to form. Serologic testing performed too early in the infection can result in false-negative results. In these cases, patients can be retested 6-12 months later. Some patients never develop type-specific antibodies. 

How is neonatal herpes simplex virus diagnosed?

Herpes simplex virus (HSV) infection should be considered in neonates with mucocutaneous lesions, central nervous system abnormalities, or a septic presentation, especially in neonates who have a mother with known HSV. Swabs should be collected from the conjunctivae, mouth, nasopharynx, rectum, and lesions (if present) for viral culture or polymerase chain reaction (PCR) testing. Lumbar puncture should be performed to provide a cerebrospinal fluid (CSF) sample for PCR testing. A blood sample should also be sent for PCR testing. Serologic tests are not helpful in the diagnosis of neonatal HSV. 

How is herpes simplex virus encephalitis diagnosed?

Herpes simplex virus (HSV) encephalitis generally presents with a rapid onset of fever, headache, seizures, focal neurologic signs, and impaired consciousness, in patients of all age groups. A lumbar puncture should be performed to obtain a cerebrospinal fluid (CSF) sample for polymerase chain reaction (PCR) testing. 

Indications for Testing

Persons with signs or symptoms of HSV infection should be tested. Additionally, type-specific testing can be considered for persons with recurrent genital symptoms or atypical symptoms who have negative HSV PCR or culture results, those with a clinical diagnosis of genital herpes without laboratory confirmation, persons with a partner who has genital herpes, and persons with HIV infection or at high risk for HIV acquisition, including those with multiple sexual partners and men who have sex with men.  Per the U.S. Preventive Services Task Force (USPSTF), screening of asymptomatic individuals in the general population for HSV-1 and HSV-2 is not indicated, including during pregnancy. 

Laboratory Testing

Virologic Testing (for Direct Detection of HSV Infection)
Test Methodology Uses/Benefits Limitations
NAAT (PCR)

Preferred method of testing CSF and blood

Highly sensitive and specific

Rapid diagnostic testing

Subtyping may be included

May yield false-negative results early in disease

Data are lacking for use of NAAT to test neonatal swab samples

Viral culture

Traditional gold standard test to identify acute HSV infection in active lesions

Preferred method to test samples from lesions or mucous membrane swabs in neonates

High specificity

Subtyping may be included

Not as sensitive as PCR for other samples, including CSF and blood

Decreases in sensitivity with disease progression, recurrent infections, and as acute lesions begin to heal

May yield false-negative results later in disease

Antigen detection by DFA

Not generally preferred

May be helpful to identify acute HSV infection in active lesions

Lower sensitivity

Backup culture required to confirm negative or indeterminate results

Typing not included

Serologic Testing

Serology, type 1 and/or 2, IgG Confirmation of HSV exposure in the absence of active lesions

Cannot determine time of exposure or site of infection

Includes antibodies to both type 1 and type 2 and cannot differentiate between them

False-negative results may occur early in disease because antibodies take 10-21 days to form

Serology, type 1 and type 2 glycoprotein, IgG

Epidemiologic data collection

Potentially useful in patient counseling regarding acquisition of virus

Can differentiate between type 1 and type 2

Results do not change clinical treatment

False-negative results may occur early in disease because type-specific antibodies can take an average of 2-3 weeks and up to 6 months to form

Some patients never develop type-specific antibodies

Cross-reactivity between subtypes may occur

Serology, IgM Not recommended for clinical use

Lacks specificity due to cross-reactivity with other herpes viruses

Results are not clinically significant

CSF, cerebrospinal fluid; DFA, direct fluorescent antibody testing; IgG, immunoglobulin G; IgM, immunoglobulin M; NAAT, nucleic acid amplification testing

Diagnosis

Genital Herpes

Genital herpes is a chronic, lifelong infection. HSV-2 is the primary cause of genital herpes; however, HSV-1 is responsible for a growing number of cases. HSV can be transmitted easily and virus can be shed even when symptoms are mild or not apparent. Most people positive for HSV-2 have not been diagnosed with genital herpes and may not realize they have it. Treatment for HSV-1 and HSV-2 are the same. Antivirals can reduce the severity and frequency of symptoms and transmission of the virus but are not curative. Infection with HSV-2 also increases the risk of acquiring HIV infection (refer to the ARUP Consult Human Immunodeficiency Virus topic and Human Immunodeficiency Virus in Adults and Adolescents Testing Algorithm). Clinical suspicion for genital herpes should be confirmed by laboratory testing. The presentation is not often classic and may be similar to the presentation of other conditions, including syphilis and chancroid. Confirming the diagnosis is important for proper patient management. 

The best way to confirm the diagnosis is by virologic testing of samples from active lesions. Viral culture was the gold standard; however, more recently, PCR has been shown to be more sensitive and is generally preferred over culture. Sensitivity decreases as the disease progresses, as lesions heal, and in recurrences. A negative test in the presence of active lesions does not rule out HSV because viral shedding is intermittent. 

If there are no active lesions but exposure to HSV is suspected, serologic testing may be used. IgG to HSV-1/2 develops before type-specific IgG to HSV-1 and HSV-2 glycoproteins, which take an average of 2-3 weeks and up to 6 months to develop. If the suspected exposure was very recent, IgG to HSV-1/2 should be tested first, with reflex to the type-specific antibodies. If the exposure was in the past, type-specific testing for IgG to HSV-1 and HSV-2 glycoproteins alone can be performed. If suspicion is high but results are negative, testing should be repeated 6-12 months later, given that false-negative results can occur, especially early in the disease. Some patients never develop type-specific antibodies. A positive IgG result cannot determine the exact time of exposure or the site of infection. IgM testing is not recommended because it is unreliable for acute infection and has been shown to cross-react with other herpes viruses.  

Neonatal HSV

HSV can be transmitted from an infected mother to the neonate during pregnancy, during delivery, or after delivery. The risk is highest during delivery, especially if the mother acquired genital herpes near the time of delivery. All pregnant women should be asked whether they have a history of genital herpes, and at the onset of labor, they should be questioned about symptoms and examined for lesions. Those with genital lesions at the onset of labor should deliver by cesarean delivery to reduce the risk of transmission. Although routine screening of mothers for HSV is not recommended, serologic testing may be used to assess risk in patients with a sex partner with a known diagnosis of HSV. Women are counseled to abstain from vaginal intercourse during the third trimester with partners known to have or suspected of having genital herpes. 

Neonatal herpes infection can present as disseminated infection involving multiple organ systems, with central nervous system involvement, or with only mucocutaneous involvement. If there is clinical suspicion for HSV, specimens should be obtained for viral culture from the conjunctivae, mouth, nasopharynx, rectum, and any lesions. Viral culture is still recommended for these specimens because there are not enough data relating to use of PCR testing in this population. CSF and blood samples, however, should be tested with PCR. Serologic testing in neonates is not helpful, given that detected HSV IgG antibodies are most likely transplacentally acquired maternal antibodies. 

HSV Encephalitis

HSV is the most common cause of nonepidemic, sporadic, acute focal encephalitis in the U.S. The majority of cases are caused by HSV-1 in adults. Without treatment, these cases of encephalitis have a mortality rate of approximately 70%. The clinical presentation is nonspecific and the differential diagnosis includes St. Louis encephalitis, Eastern equine encephalitis, and Epstein-Barr viruses, among others. Thus, early identification of HSV and appropriate treatment are very important to the clinical course. 

The recommended test for HSV encephalitis is PCR on a CSF sample obtained by lumbar puncture. Viral culture lacks sensitivity in CSF, and the previous gold standard, brain biopsy, is invasive and slow. PCR can be falsely negative, especially in children and early in the disease course. If PCR is negative and there is clinical suspicion for HSV, a second lumbar puncture should be performed within 3-7 days and the CSF should be tested. Serologic testing on CSF is available but often not clinically useful. 

Screening

According to the USPSTF, screening of asymptomatic individuals for HSV-1 and HSV-2 in the general population is not indicated, including during pregnancy. 

Immunocompromised Patients

Immunocompromised patients, including those positive for HIV and those who have undergone transplants, can be at higher risk for more severe HSV infections. When the immune system is weakened, the ability to maintain HSV in the latent state is decreased, which results in increased frequency and severity of mucocutaneous recurrences as well as the possibility of dissemination of the disease to other organ systems. In these cases, antibody testing will not be helpful and PCR testing should be used. 

Antiviral Susceptibility Testing

HSV may become resistant to the first-line treatment, acyclovir, especially in patients infected with HIV. Foscarnet can be used to treat acyclovir-resistant HSV in these cases. Resistance to foscarnet can also occur, mostly in patients with previous exposure to the drug. Susceptibility testing for acyclovir and foscarnet is available to help guide treatment when patients are not responding to these medications. 

ARUP Laboratory Tests

Preferred Tests for Genital Herpes

Use to confirm active genital herpes infection

Specimen type: vesicle fluid

Use to confirm genital herpes in the absence of lesions in patients with suspected recent exposure

Specimen type: blood

Use to confirm past exposure to HSV

Specimen type: blood

Preferred Tests for Neonatal HSV

Use to diagnose neonatal HSV

Specimen type: CSF or blood

Use to diagnose neonatal HSV

Specimen type: buccal mucosa, eye, genital, rectal, throat, or vesicle swab, or bronchoalveolar lavage fluid, tissue, or vesicle fluid

Preferred Test for HSV Encephalitis

Use to diagnose HSV encephalitis

Specimen type: CSF

Antiviral Susceptibility Tests

Use to detect HSV resistance to foscarnet

Specimen type: buccal mucosa, eye, genital, rectal, throat, or vesicle swab, or bronchoalveolar lavage fluid, tissue, or vesicle fluid

Use to detect HSV resistance to acyclovir

Specimen type: buccal mucosa, eye, genital, rectal, throat, or vesicle swab, or bronchoalveolar lavage fluid, tissue, or vesicle fluid

Other Available Tests

Medical Experts

Author

Leonard

Picture of Nicole Leonard, MD

 

Anatomic and Clinical Pathology Resident, University of Utah School of Medicine and ARUP Laboratories
Contributor

Slev

Patricia R. Slev, PhD
Associate Professor of Pathology (Clinical), Codirector, Clinical Chemistry Fellowship program, University of Utah
Section Chief, Immunology; Medical Director, Immunology Core Laboratory; Medical Director, Serologic Hepatitis and Retrovirus and Immunology Core Laboratory; Co-Medical Director, Microbial Immunology, ARUP Laboratories

References