HSV-1& HSV-2 Type Specific Serologic & Virologic Assays

HSV-1 AND HSV-2 TYPE SPECIFIC SEROLOGIC AND VIROLOGIC ASSAYS
By Wesley J Kim, M.D., DLS Pathologist, January 2003

Herpes simplex virus (HSV) is a common human pathogen found worldwide and is one of the most prevalent STDs in the United States. It is estimated that nearly 50 million people in the United States are infected with HSV (1), with the estimated number of new cases now approaching 1 million per year (2).

HSV is a member of the family Herpesviridae, which also includes varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, and human herpes viruses 6, 7, and 8 (3). It is a double-stranded DNA virus composed of a central core containing the DNA genome, a capsid, a tegument layer, and a spiked envelope (4). The spikes are viral glycoproteins that facilitate adhesion of the virus to the target cell. Following attachment the viral envelope and cell membrane fuse, allowing the capsid to enter the cell (4). The capsid migrates to the nucleus where it releases its viral DNA and replication ensues. The replicated DNA is repackaged in a capsid and envelope and released from the cell membrane where it can be taken up by surrounding neuronal axons and transported to the nucleus where it can become latent, with subsequent reactivation at a later date (4).

Humans are the exclusive reservoir of HSV. Transmission is the result of direct contact, sexual or non-sexual, with infected secretions from either asymptomatic or asymptomatic host. Infections range in severity from subclinical to life-threatening and can affect any age group, from neonates to children to adults.
There are two serologic subtypes of HSV: HSV-1 and HSV-2 (3). In general, HSV-1 is associated with orolabial infections: gums, mouth, lip, face, and/or pharynx. Typical symptoms include painful lesions and/or fever, although symptoms may be absent. Recurrent infections can occur in up to 40% and manifest as “cold sores” or blisters around the mouth. Importantly, HSV-1 is increasingly recognized as a cause of genital herpes, accounting for up to 30% of cases in the US (1). HSV-2 is more commonly associated with genital infections (3), accounting for 70 to 90% of cases of primary genital herpes, manifesting as bilateral lesions in the genital area accompanied by fever, inguinal adenopathy, and dysuria. However, up to 80% of infections may go undiagnosed because they are either asymptomatic or unrecognized by the patient or physician (5).

Primary genital herpes infection in pregnancy is particularly concerning as it can result in spontaneous abortion, low birth weight, premature delivery, and neonatal herpes, which itself can present with localized infection, encephalitis, and/or disseminated infection. Approximately 30% of HSV-1 and 50% of HSV-2 neonatal infections result in death or serious residual disability (6). Antiviral chemotherapeutic agents against HSV are available (1, 7), therefore timely and accurate diagnostic methods are important.
Unfortunately, the diagnosis of genital herpes based on clinical and physical examination is both insensitive and non-specific (1, 8). Most neonatal infections result from asymptomatic shedding from mothers who have acquired genital herpes in late pregnancy (9, 10). The challenge is identify those mothers at risk and then apply interventions to reduce that risk. Recurrence rates for genital HSV-1 infections are also much lower than genital HSV-2 infections (1, 11). It also appears that HSV-2 infection may be a significant risk factor for HIV acquisition (12). For these reasons laboratory testing to not only confirm the diagnosis, but also differentiate between HSV-1 and HSV-2 infections, could play an increasingly important role in the proper management, prognosis, and counseling of patients.

In December 2002, Diagnostic Laboratory Services changed its HSV serology assay, and starting January 2003 will change its HSV virologic assay, to type-specific methodologies that are able to reliably differentiate between HSV-1 and HSV-2.
DLS is using the FDA-approved HerpeSelect Type-Specific HSV-1 and HSV-2 IgG diagnostic test kit from Focus Technologies, Inc., an ELISA-based test that employs the HSV type-specific glycoprotein antigens gG1 (HSV-1) and gG2 (HSV-2) to detect type-specific IgG antibodies. The sensitivity and specificity of the assay for HSV-1 ranges from 75% to 96% and 92% to 100% respectively, and for HSV-2 from 96 to 100% and 96 to 100% respectively, depending on the prevalence of infection in the populations tested. False negatives may occur at the early stages of infection prior to seroconversion. If clinical suspicion is high, repeat testing in 4-6 weeks is recommended. False positives can occur particularly in patients with a low clinical likelihood of infection. In such cases repeat testing, or in certain situations, confirmatory testing, may be indicated. A single positive result only indicates previous immunologic exposure. Use of this test for general population screening is not indicated or recommended.

DLS will also be switching to the ELVIS HSV ID/Typing Test System by Diagnostic Hybrids, Inc., a shell-vial culture method that combines the sensitivity of cell culture amplification with the specificity of HSV activated reporter genes and antigen detection via HSV-1 and HSV-2 type-specific monoclonal antibodies. The overall sensitivity and specificity are 99% and 98.3% respectively, with positive predictive values ranging from 75 to 99.4% and corresponding negative predictive values ranging from 99.9 to 97%, depending on the prevalence of infection in the populations tested.
As with all laboratory tests, results should be correlated with all other patient clinical information.

* Reflex to HSV-1 detection will be charged an additional $15.00 (Procedure Code 87254)

Unacceptable Specimens for HSV culture: Wooden shafted swabs, cotton-tipped or calcium alginate swabs, specimens other than body fluids not in viral transport media, and unfrozen specimens received > 48 hrs from collection.
For additional information or questions, please call client services at 589-5101.

References:

1. CDC. Sexually Transmitted Diseases Treatment Guidelines 2002. MMWR 2002; 51 (No. RR-6): 12-17.
2. Cates W et al. Estimates of the Incidence and Prevalence of Sexually Transmitted Diseases in the United States. Sex Trans Dis 1999; 26(suppl.): S2-S7.
3. Storch GA (ed). Essentials of Diagnostic Virology. Harcourt Brace & Co. New York, NY. 2000.
4. Lennette EH et al. Laboratory Diagnosis of Viral Infections, Third Ed. Marcel Dekker. New York, NY. 1999.
5. Gottlieb S et al. Seroprevalence and Correlates of Herpes Simplex Virus Type 2 Infection in Five Sexually Transmitted Disease Clinics. J of Inf Dis 2002; 186: 1381-9.
6. Kesson AM. Management of Neonatal Herpes Simplex Virus Infection. Paediatr Drugs 2001; 3: 91-90.
7. Wald A et al. JAMA 2001; 285: 3100-6.
8. Koutsky L et al. Underdiagnosis of Genital Herpes by Current Clinical and Viral Isolation Procedures. N Eng J of Med 1992; 326: 1533-9.
9. Brown ZA et al. The Acquisition of Herpes Simplex Virus during Pregnancy. N Eng J of Med 1997; 337: 509-15.
10. Eskild A et al. Herpes Simplex Virus Type-2 in Pregnant Women: The Impact of the Stage of Pregnancy. Epidemiol Infect 2000; 125: 685-92.
11. Benedetti JK et al. Clinical Reactivation of Genital Herpes Simplex Virus Infection Decreases in Frequency over Time. Ann Intern Med 1999; 131: 14-20.
12. Wald A et al. Risk of Human Immunodeficiency Virus Infection in Herpes Simplex Virus Type-2 Seropositive Person: A meta-Analysis. J Infect Dis 2002; 185: 45-51.