Literature review > Issue 7 > Review on Whiley et al. 

This comparison study was nicely done and well described; thus providing little fodder for controversy or complaint. Whiley and colleagues have provided an interesting base for reflection on the status of the field with respect to diagnosing HSV lesions. For years, inoculation of cell cultures has been considered the gold standard test. As recently as 2002, the CDC STD Treatment Guidelines stipulated that isolation of HSV in cell culture was the preferred virologic test for patients presenting with mucocutaneous lesions [1]. Culture provides amplification of the virus for detecting low input titers of HSV and can, therefore, be a sensitive measure of infection. However, the specificity of the cytopathic effect, even as observed by trained technologists, is less than perfect. Enteroviruses and varicella zoster virus, in particular, can masquerade as HSV CPE.

Thus, when monoclonal antibody technology came into the commercial arena in the 1980s, typing of HSV isolates as HSV-1 or HSV-2 became routine. Use of typing reagents allowed definitive HSV diagnosis (ruling out other viruses) and thus improved the specificity of culture. These reagents could also be used directly on smears of cells from patient lesions, a quicker test but far less sensitive than culture. The application of DNA amplification technology and particularly the use of real-time PCR techniques have, once again, dramatically changed the testing arena for HSV. These tests are far more sensitive than culture [2] and do not require infectious virus; an important advance in an era of increasing concern about transport of biohazardous materials. Early PCR tests were exacting and required strict adherence to protocols to prevent cross-contamination of samples. Newer, closed systems like LightCycler or TaqMan have removed much of that risk while reducing test time to a few hours. PCR-based tests are, in fact, accurate enough to have become the gold standard test for diagnosis of HSV infections of the central nervous system and for neonatal herpes.

Still, in their discussion of PCR, the CDC 2002 STD Guidelines state "… their role in the diagnosis of genital ulcer disease has not been well-defined." As we approach 2005, potential roles for PCR are emerging. In particular, PCR, along with type specific serology, can play a critical role in diagnosing new and recurrent infections that manifest as localized skin splits, erosions, and irritated areas. These lesions are often false negative by culture due to low titer shedding, brief duration of shedding, or loss of viability in transit to the lab.

In many such cases, glycoprotein G-based antibody tests are very useful and cost effective in confirming a clinical impression of genital herpes especially if clinical signs are subtle. ELISAs from Focus and more recently those from Trinity; immunoblot tests from Focus, and point of care tests such as biokitHSV-2 and SureVue HSV-2 (both from Biokit; previously marketed as POCkitHSV-2 from Diagnology) can detect HSV-2 antibodies even in patients who are falsely negative by culture. However, these tests do not reveal the anatomic source of infection that gives rise to HSV-1 antibodies. In addition, each serology has a "gray zone" in which the result is "indeterminate" in 3-5% of sera and in a higher percentage of sera during seroconversion. Type-specific PCR can detect infection before antibodies develop and in patients with indeterminate serology, if samples are taken during periods of virus excretion.

Considerable clinical overlap exists between presentation of genital herpes and other genital infections [3]. Direct tests like PCR can resolve the etiology of an ulcer; multiplexed tests provide definitive answer for lesions containing more than one agent [4]. PCR-type tests have the potential to identify HSV in the genital tract of pregnant women presenting for delivery [5].

Finally, for some patients, a direct definitive virologic test performed on a sample from a genital site is emotionally beneficial, providing some closure on a difficult diagnosis and a starting point for discussion on management [6]. From the public health point of view, a sensitive virologic test like PCR provides a definitive answer for partner counseling and patient management to prevent transmission [7]. With the increased understanding of the effect of HSV infection on transmission of HIV, there is greater interest in using the most accurate test or test combination to identify patients with genital herpes [8].

To achieve wide acceptance, PCR tests need to be rapid, easy to perform, accurate, and inexpensive. The messages that we take from this paper and other work are 3-fold. First, DNA amplification tests should be based on type-specific primers and should include internal controls for the presence of enzyme-inhibiting factors that could lead to false negative results. While LightCycler tests are rapid and amenable to development protocols, the authors point out that they are limited in the number of simultaneous assays that can be performed. Next, PCR is still too costly to perform routinely in the scenarios proposed above. Sample processing is labor intensive and robotic test formats require substantial capital expenditures for moderate volume labs. For the near term, test price may well continue to limit the role of PCR in diagnosis of genital herpes. Finally, better methods are needed. In the next decade, microarray technology may deliver the promise of rapid, moderately priced, accurate testing of local mucocutaneous sites for HSV-1 and HSV-2 and other etiologic agents of genital ulcers. In combination with type specific serology, such tests may give definitive and quick answers for every clinical scenario.

References:

1. Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines 2002; MMWR 2002;51(no. RR-6) 1-25.

2. Wald A, Huang ML, Carrell D, Selke S, Corey L. Polymerase chain reaction for detection of herpes simplex virus (HSV) DNA on mucosal surfaces: comparison with
HSV isolation in cell culture. J Infect Dis 2003; 188:1345-51.

3. Handsfield HH. Genital Herpes. The McGraw-Hill Company New York NY, 2001.

4. Mertz KJ, Trees D, Levine WC. Etiology of genital ulcers and prevalence of human
immunodeficiency virus coinfection in 10 US cities. J Infect Dis 1998;178:1795-98.

5. Brown ZA, Ashley RL, Selke S, Zeh J, Wald A, Corey L. Effect of serologic status and cesarean delivery on transmission rates of herpes simplex virus from mother to
infant. JAMA 2003; 289:203-9.

6. Warren T. Importance and practicalities of patient counseling in the prevention an
management of genital herpes. Medscape Infect Dis 2004; 6(2).

7. Corey L, Wald A, Patel R, Sacks SL, Tyring SK, Warren T, Douglas JM, Paavonen J, Ashley Morrow R, Beutner KR, Stratchounsky LS, Keene ON, Watson HA, Tait D, Vargas-Cortez M, for the Valacyclovir HSV Transmission Study Group. Once daily valacyclovir to reduce the risk of transmission of genital herpes. N Engl J Med 2004;
350:11-20.

8. Wald A and Corey L. How does herpes simplex virus type 2 influence human immunodeficiency virus infection and pathogenesis. J Infect Dis 2003; 187:1509-12

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