The development of resistance usually results from mutations within the viral genome, and the presence of selective drug pressure usually results in the emergence of a resistant virus population.
The isolation of HSV from persisting lesions despite adequate dosages and blood levels of acyclovir should raise the suspicion of acyclovir resistance. The antiviral activity of acyclovir requires an initial phosphorylation step by the viral enzyme thymidine kinase TK 45 , Two subsequent phosphorylation steps are mediated by cellular kinases. The resulting triphosphorylated acyclovir then specifically inhibits herpesvirus DNA polymerases.
Three different mechanisms of resistance of HSV to acyclovir have been identified. The most common is found in viruses that lack a functional TK TK - mutants and, thus, are unable to monophosphorylate acyclovir. Less commonly, some resistant viruses produce a functional TK enzyme that is unable to phosphorylate acyclovir because of altered substrate specificity TK A mutants.
Foscarnet directly inhibits herpesvirus DNA polymerases and resistance develops because of altered viral DNA polymerases.
Vidarabine resistance also occurs rarely. Vidarabine is phosphorylated by cellular enzymes and then inhibits virally encoded DNA polymerase.
The complexity of drug sensitivity assays for antiviral resistance limits their availability. At the present time, they are only performed by specialized laboratories. Susceptibility testing of strains of HSV against various antiviral agents is usually performed in the laboratory using modifications of one of the following: plaque reduction assays, dye uptake assays or DNA hybridization assays 45 , The plaque reduction assay was the first antiviral susceptibility testing method performed to determine the susceptibility of viruses to antiviral agents and is the standard against which other tests are compared.
These tests are time consuming and may soon be replaced by genotypic tests that can be processed more quickly. All laboratories providing diagnostic services for the detection of HSV in clinical samples or performing HSV serological assays must participate in the testing of proficiency panels provided by external agencies whenever possible for all tests performed. If proficiency testing for specific assays is not available eg, HSV DNA detection in swab material or type-specific serological testing , then specimen exchange among laboratories performing such testing should be arranged as an alternative form of proficiency testing.
Subpassages of HSV clinical isolates should be inoculated with each batch of HSV roller tube or shell vial cultures to serve as positive controls. Uninfected tubes or shell vial cultures serve as negative controls. Both infected and uninfected cell monolayers should be observed for the presence or absence of HSV CPE and stained to observe for typical immunofluorescence with HSV monoclonal antibodies.
Positive controls should exhibit characteristic CPE and immunofluorescence with type-specific antisera, while negative controls should not. Variations in sensitivity may occur in cultured cell lines for various reasons.
Positive and negative control slides should be included daily in each run to ensure that the antibody reagents are performing correctly. Typical immunofluorescence should be observed in the positive controls but not the negative controls.
Positive and negative controls must be included with each batch of sera tested. When commercial kits are used, these controls are usually provided in the kit. Results obtained in serology assays should be discarded and not be reported if control samples are out of the expected range. In addition, the use of in-house positive and negative controls should be considered.
Run-to-run variability in readings on the control samples should be tracked. Testing of new lots of kits should be performed before their use in the laboratory. Most laboratories undertake regular tests to determine analytical sensitivity and specificity of any in-house procedures. Weak positive controls should be included in every PCR run to ensure consistent sensitivity of the assay along with negative extraction and amplification controls to assess any potential problems with contamination that could lead to false-positive results.
Internal controls may be used to detect the presence of any amplification inhibitors that could lead to false-negative results, although this is rarely a problem. The authors are indebted to Dr Bonita Lee and Barbara LeBlanc for their invaluable comments and review of the manuscript.
The authors would like to dedicate this article to the memory of Dr Stephen Sacks, whose work contributed to significant advances in HSV infections. National Center for Biotechnology Information , U. Author information Copyright and License information Disclaimer.
Telephone , fax , e-mail ac. All rights reserved. This article has been cited by other articles in PMC. Abstract Herpes simplex virus HSV types 1 and 2 cause genital herpes infections and are the most common cause of genital ulcer disease in industrialized nations.
Specimen Choice, Collection And Transport Direct methods Specimens obtained from vesicular lesions within the first three days after their appearance are the specimens of choice, but other lesion material from older lesions or swabs of genital secretions should be obtained if suspicion of HSV infection is high 10 , Indirect serological methods Approximately 8 mL to 10 mL of blood is usually collected in tubes without anticoagulant or preservatives.
Diagnostic Tests Direct methods Direct tests endeavour to demonstrate the presence of HSV in a suspicious lesion or in genital secretions. Viral isolation Standard viral culture: Tube culture isolation is the traditional gold standard for HSV detection and the reference method against which all other tests are measured 16 , Shell vial or centrifugation-enhanced culture: Many laboratories now use centrifugation-enhanced shell vial culture methods to reduce viral isolation times Antigen detection Viral antigen detection may be a suitable alternative to culture for smaller laboratories in which the expense of maintaining cell lines is unwarranted.
Tzanck smears HSV infection causes typical cytopathic changes in genital epithelial cells 3. Electron microscopy Direct examination of vesicle fluid or other clinical material by electron microscopy for the diagnosis of HSV is limited by the fact that viral morphology cannot be used to distinguish HSV from other herpes viruses eg, varicella zoster virus Indirect Serological Tests The detection of antibodies to HSV allows for diagnosis when other virological methods cannot be performed or yield negative results Seroepidemiological studies Seroprevalence studies Seroincidence studies Sexual transmission studies Current and potential clinical uses Patients with apparent first episode and recurrent genital herpes, especially pregnant women Clinically discordant couples, particularly where the man is positive and the woman is negative and of child-bearing potential Women of child-bearing potential with a history of lesions suspicious for genital herpes where repeated direct testing for HSV has been negative Sexually transmitted infection screening, especially those at risk of acquiring HIV infection Diagnosis of genital herpes when lesions tested using direct tests are negative on at least two occasions Screening of all HIV-infected individuals at the time of initial diagnosis with HIV, with a view to providing suppressive HSV antiviral therapy in those found to be HSV-2 antibody-positive.
Open in a separate window. Reproduced with permission from reference 2. Commercial gG-based type-specific tests Although most of the available literature evaluating the performance of type-specific tests was based on kits developed by Gull Laboratories USA , these tests have now been withdrawn from the market. Antiviral Resistance Testing A number of antiviral agents have been developed for the management of HSV infections; of these, acyclovir is the most commonly used.
Drug sensitivity assays The complexity of drug sensitivity assays for antiviral resistance limits their availability. Proficiency And Quality Assurance All laboratories providing diagnostic services for the detection of HSV in clinical samples or performing HSV serological assays must participate in the testing of proficiency panels provided by external agencies whenever possible for all tests performed.
Culture Subpassages of HSV clinical isolates should be inoculated with each batch of HSV roller tube or shell vial cultures to serve as positive controls. Direct smears Positive and negative control slides should be included daily in each run to ensure that the antibody reagents are performing correctly. Indirect serological methods Positive and negative controls must be included with each batch of sera tested. Acknowledgments The authors are indebted to Dr Bonita Lee and Barbara LeBlanc for their invaluable comments and review of the manuscript.
References 1. Herpes simplex virus type 2 in the United States, to N Engl J Med ; Corey L. The current trend in genital herpes. Progress in prevention. Sex Transm Dis ; 21 Suppl 2 :S The Tzanck smear in the diagnosis of cutaneous herpes simplex.
JAMA ; Corey L, Spear PG. Infections with herpes simplex viruses 1. Ashley RL. These agents, acyclovir, valaciclovir, and famciclovir, all accelerate the events of healing and decrease the probability of excreting the virus when they are taken in a suppressive fashion. The long-term safety of acyclovir has been unequivocally established. Its prodrug, valaciclovir, and the prodrug of penciclovir, famciclovir, have not been used in practice as long and, therefore, less is known about these agents; however, neither is available as a pediatric formulation.
Author information Copyright and License information Disclaimer. This article has been cited by other articles in PMC. Keywords: herpes simplex virus, seroprevalence. For appropriate clinical management and complete patient counselling, the type of virus needs to be identified What do these changes imply for clinicians? References 1. Sex Transm Infect 82 — Clinical and virological studies on genital herpes. Lancet 2 [ PubMed ] [ Google Scholar ]. Incidence and distribution of herpes simplex virus types 1 and 2 from genital lesions in college women.
J Med Virol 1 — Antimicrob Agents Chemother 38 — Sex Transm Infect 76 — Some people experience numerous episodes each year. For many people, however, the outbreaks are less frequent as time passes. However, recurrences are generally less painful than the original outbreak, and sores generally heal more quickly.
If you suspect you have genital herpes — or any other sexually transmitted infection — see your doctor. Because the virus dies quickly outside of the body, it's nearly impossible to get the infection through contact with toilets, towels or other objects used by an infected person. The suggestions for preventing genital herpes are the same as those for preventing other sexually transmitted infections: Abstain from sexual activity or limit sexual contact to only one person who is infection-free.
Short of that, you can:. If you're pregnant and know you have genital herpes, tell your doctor. If you think you might have genital herpes, ask to be tested for it. Your doctor may recommend that you start taking herpes antiviral medications late in pregnancy to try to prevent an outbreak around the time of delivery.
If you're having an outbreak when you go into labor, your doctor will probably suggest a cesarean section to reduce the risk of passing the virus to your baby. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press.
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