Resistant herpes simplex virus type 1 infection: an emerging concern after allogeneic stem cell transplantation

Herpes simplex virus type-1 (HSV-1) entry into human mesenchymal stem cells is heavily dependent on heparan sulfate

Hematopoietic stem cells recipients remain susceptible to opportunistic viral infections including herpes simplex virus type-1 (HSV-1). The purpose of this investigation was to analyze susceptibility of human mesenchymal stem cells (hMSCs) to HSV-1 infection and identify the major entry receptor. Productive virus infection in hMSCs was confirmed by replication and plaque formation assays using a syncytial HSV-1 KOS (804) virus. To examine the significance of entry receptors, RT-PCR and antibody-blocking assays were performed. RT-PCR data showed the expression of gD receptors: nectin-1, 3-O sulfotransferase-3 (3-OST-3), and HVEM. Antibody-blocking assay together with heparinase treatment suggested an important role for HS and 3-O-sulfated heparan sulfate (3-OS HS), but not nectin-1 or HVEM, in mediating HSV-1 entry and spread in hMSCs. Taken together, our results provide strong evidence demonstrating that HSV-1 is capable of infecting hMSCs and HS and 3-OS HS serve as its entry receptors during this process.

Expression of herpes simplex virus type 1 recombinant thymidine kinase and its application to a rapid antiviral sensitivity assay

Antiviral-resistant herpesvirus infection has become a great concern for immunocompromised patients. Herpes simplex virus type 1 (HSV-1) infections are treated with viral thymidine kinase (vTK)-associated drugs such as acyclovir (ACV), and most ACV-resistance (ACV(r)) is due to mutations in the vTK. The standard drug sensitivity test is usually carried out by the plaque reduction assay-based method, which requires over 10 days. To shorten the time required, a novel system was developed by the concept, in which 293T cells transiently expressing recombinant vTK derived from the test sample by transfection of the cells with an expression vector were infected with vTK-deficient and ACV(r) HSV-1 (TAR), and then cultured in a maintenance medium with or without designated concentrations of ACV, ganciclovir (GCV) and brivudine (BVdU). The replication of TAR was strongly inhibited by ACV, GCV and BVdU in 293T cells expressing recombinant vTK of the ACV-sensitive HSV-1, whereas replication was not or slightly inhibited in cells expressing the recombinant vTK of highly resistant or intermediately resistant HSV-1, respectively. An inverse correlation was demonstrated in the 50% effective concentrations (EC(50)s) and inhibitory effects of these compounds on the replication of TAR among ACV(s) and ACV(r) HSV-1 clones. These results indicate that the EC(50)s of the vTK-associated drugs including ACV can be assumed by measuring the inhibitory effect of drugs in 293T cells expressing recombinant vTK of the target virus. The newly developed antiviral sensitivity assay system for HSV-1 makes it possible to estimate EC(50) for vTK-associated drugs, when whole vTK gene is available for use by gene amplification directly from lesion's samples or from virus isolates.

Herpes viruses in transplant recipients: HSV, VZV, human herpes viruses, and EBV

The herpes viruses are responsible for a wide range of diseases in patients following transplant, resulting from direct viral effects and indirect effects, including tumor promotion. Effective treatments and prophylaxis exist for the neurotropic herpes viruses HSV-1, HSV-2, varicella zoster virus, and possibly HHV-6. Antivirals seem to be less effective at prevention of the tumor-promoting effects of Epstein-Barr virus and HHV-8. Reduction in immunosuppression is the cornerstone to treatment of many diseases associated with herpes virus infections.

Synthesis and anti-HSV-1 activity of new 1,2,3-triazole derivatives

In this work, a new series of arysulfonylhydrazine-1H-1,2,3-triazole derivatives were synthesized, and their ability to inhibit the in vitro replication of HSV-1 was evaluated. Among the 1,2,3-triazole derivatives, 1-[(5″-methyl-1″-(4‴-fluorophenylamino)-1H-1,2,3-triazol-4″-yl)carbonyl]-2-(4'-methylphenylsulfonyl)hydrazine and 1-[(5'-methyl-1'-(2″,5″-dichlorophenylamino)-1H-1,2,3-triazol-4'-yl)carbonyl]-2-(phenylsulfonyl)hydrazine, with IC(50) values of 1.30 and 1.26 μM, respectively, displayed potent activity against HSV-1. Because these compounds have low cytotoxicity, their selectivity indices are high. Under the assay conditions, they have better performance than does the reference compound acyclovir. The structures of all of the compounds were confirmed by one- and two-dimensional NMR techniques ((1)H, (13)C-APT, COSY-(1)H×(1)H and HETCOR (1)J(CH)) and by elemental analysis.

Hydrolyzable tannins (chebulagic acid and punicalagin) target viral glycoprotein-glycosaminoglycan interactions to inhibit herpes simplex virus 1 entry and cell-to-cell spread

Herpes simplex virus 1 (HSV-1) is a common human pathogen that causes lifelong latent infection of sensory neurons. Non-nucleoside inhibitors that can limit HSV-1 recurrence are particularly useful in treating immunocompromised individuals or cases of emerging acyclovir-resistant strains of herpesvirus. We report that chebulagic acid (CHLA) and punicalagin (PUG), two hydrolyzable tannins isolated from the dried fruits of Terminalia chebula Retz. (Combretaceae), inhibit HSV-1 entry at noncytotoxic doses in A549 human lung cells. Experiments revealed that both tannins targeted and inactivated HSV-1 viral particles and could prevent binding, penetration, and cell-to-cell spread, as well as secondary infection. The antiviral effect from either of the tannins was not associated with induction of type I interferon-mediated responses, nor was pretreatment of the host cell protective against HSV-1. Their inhibitory activities targeted HSV-1 glycoproteins since both natural compounds were able to block polykaryocyte formation mediated by expression of recombinant viral glycoproteins involved in attachment and membrane fusion. Our results indicated that CHLA and PUG blocked interactions between cell surface glycosaminoglycans and HSV-1 glycoproteins. Furthermore, the antiviral activities from the two tannins were significantly diminished in mutant cell lines unable to produce heparan sulfate and chondroitin sulfate and could be rescued upon reconstitution of heparan sulfate biosynthesis. We suggest that the hydrolyzable tannins CHLA and PUG may be useful as competitors for glycosaminoglycans in the management of HSV-1 infections and that they may help reduce the risk for development of viral drug resistance during therapy with nucleoside analogues.

Resistance of herpes simplex viruses to nucleoside analogues: mechanisms, prevalence, and management

Herpes simplex viruses (HSV) type 1 and type 2 are responsible for recurrent orolabial and genital infections. The standard therapy for the management of HSV infections includes acyclovir (ACV) and penciclovir (PCV) with their respective prodrugs valacyclovir and famciclovir. These compounds are phosphorylated by the viral thymidine kinase (TK) and then by cellular kinases. The triphosphate forms selectively inhibit the viral DNA polymerase (DNA pol) activity. Drug-resistant HSV isolates are frequently recovered from immunocompromised patients but rarely found in immunocompetent subjects. The gold standard phenotypic method for evaluating the susceptibility of HSV isolates to antiviral drugs is the plaque reduction assay. Plaque autoradiography allows the associated phenotype to be distinguished (TK-wild-type, TK-negative, TK-low-producer, or TK-altered viruses or mixtures of wild-type and mutant viruses). Genotypic characterization of drug-resistant isolates can reveal mutations located in the viral TK and/or in the DNA pol genes. Recombinant HSV mutants can be generated to analyze the contribution of each specific mutation with regard to the drug resistance phenotype. Most ACV-resistant mutants exhibit some reduction in their capacity to establish latency and to reactivate, as well as in their degree of neurovirulence in animal models of HSV infection. For instance, TK-negative HSV mutants establish latency with a lower efficiency than wild-type strains and reactivate poorly. DNA pol HSV mutants exhibit different degrees of attenuation of neurovirulence. The management of ACV- or PCV-resistant HSV infections includes the use of the pyrophosphate analogue foscarnet and the nucleotide analogue cidofovir. There is a need to develop new antiherpetic compounds with different mechanisms of action.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

Use of acyclovir for suppression of human immunodeficiency virus infection is not associated with genotypic evidence of herpes simplex virus type 2 resistance to acyclovir: analysis of specimens from three phase III trials

Herpes simplex virus type 2 (HSV-2) is the most common cause of genital ulcer disease and is a cofactor for HIV-1 acquisition and transmission. We analyzed specimens from three separate phase III trials of acyclovir (ACV) for prevention of HIV-1 acquisition and transmission to determine if failure of ACV to interrupt HIV acquisition and transmission was associated with genotypic ACV resistance. Acyclovir (400 mg twice daily) or placebo was provided to HSV-2-infected persons at risk of HIV-1 infection in the Mwanza and HPTN 039 trials and to persons dually infected with HSV-2 and HIV-1 who had an HIV-negative partner in the Partners in Prevention study. We extracted HSV DNA from genital ulcer swabs or cervicovaginal lavage fluids from 68 samples obtained from 64 participants randomized to ACV and sequenced the HSV-2 UL23 gene encoding thymidine kinase. The UL23 sequences were compared with published and unpublished data. Variants were observed in 38/1,128 (3.4%) nucleotide positions in the UL23 open reading frame, with 58% of these encoding amino acid changes. No deletions, insertions, or mutations known to be associated with resistance were detected. Thirty-one of the variants (81.5%) are newly reported, 15 of which code for amino acid changes. Overall, UL23 is highly polymorphic compared to other loci in HSV-2, but no drug resistance mutations were detected that could explain the failure to reduce HIV incidence or to prevent HIV-1 transmission in these studies.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

Treatment of acyclovir-resistant herpes simplex virus with continuous infusion of high-dose acyclovir in hematopoietic cell transplant patients

Infection because of herpes simplex virus (HSV) that is resistant to acyclovir (ACV) poses treatment challenges in hematopoietic cell transplant (HCT) patients. We present a series of patients with ACV-resistant HSV following HCT who were successfully treated with continuous infusion high-dose ACV after failing standard treatment regimens for ACV-resistant HSV.

Acyclovir resistance in herpes simplex encephalitis

Herpes simplex virus type 1 is a common cause of severe sporadic encephalitis. Treatment with acyclovir is highly effective in this disease. We report the case of a 27-year-old, immunocompetent woman with acyclovir-resistant herpes simplex encephalitis. Although she had not been treated before, herpes simplex virus type 1 DNA from the cerebrospinal fluid showed a non-synonymous mutation in the thymidine kinase gene, which is likely to have caused resistance to acyclovir. Herpes simplex encephalitis resolved after treatment with foscarnet. To our knowledge, this is the first report of acyclovir-resistant herpes simplex virus encephalitis in an immunocompetent, previously therapy-naive adult.

Efficacy of anise oil, dwarf-pine oil and chamomile oil against thymidine-kinase-positive and thymidine-kinase-negative herpesviruses

The effect of anise oil, dwarf-pine oil and chamomile oil against different thymidine-kinase-positive (aciclovir-sensitive) and thymidine-kinase-negative (aciclovir-resistant) herpes simplex virus type 1 (HSV-1) strains was examined. Clinical HSV-1 isolates containing frameshift mutations in the thymidine kinase (TK) gene, an insertion or a deletion, yield a non-functional thymidine kinase enzyme resulting in phenotypical resistance against aciclovir. The inhibitory activity of three different essential oils against herpes simplex virus isolates was tested in-vitro using a plaque reduction assay. All essential oils exhibited high levels of antiviral activity against aciclovir-sensitive HSV strain KOS and aciclovir-resistant clinical HSV isolates as well as aciclovir-resistant strain Angelotti. At maximum noncytotoxic concentrations of the plant oils, plaque formation was significantly reduced by 96.6–99.9%, when herpesviruses were preincubated with drugs before attachment to host cells. No significant effect on viral infectivity could be achieved by adding these compounds during the replication phase. These results indicate that anise oil, dwarf-pine oil and chamomile oil affected the virus by interrupting adsorption of herpesviruses and in a different manner than aciclovir, which is effective after attachment inside the infected cells. Thus the investigated essential oils are capable of exerting a direct effect on HSV and might be useful in the treatment of drug-resistant viruses. Chamomile oil did not reveal any irritating potential on hen's egg chorioallantoic membrane, demonstrated the highest selectivity index among the oils tested and was highly active against clinically relevant aciclovir-resistant HSV-1 strains.

A perspective on antiviral resistance

More than 25 years after the licensure of aciclovir and then penciclovir, followed by their respective prodrugs valaciclovir and famciclovir, cases of clinically relevant resistance to these drugs in immunocompetent individuals remain very rare. The aim of this review is to focus on the mechanism of action of these anti HSV drugs and then briefly compare this favourable outcome with that of CMV, HIV, HBV and influenza. A central theme is that resistance is an epiphenomenon of failure to suppress virus replication, so that improved potency and selectivity should be prioritised when developing new drugs rather than activity against resistant strains per se.

Management of HSV, VZV and EBV infections in patients with hematological malignancies and after SCT: guidelines from the Second European Conference on Infections in Leukemia

These guidelines on the management of HSV, VZV and EBV infection in patients with hematological malignancies and after SCT were prepared by the European Conference on Infections in Leukemia following a predefined methodology. A PubMed search was conducted using the appropriate key words to identify studies pertinent to management of HSV, VZV and EBV infections. References of relevant articles and abstracts from recent hematology and SCT scientific meetings were also reviewed. Prospective and retrospective studies identified from the data sources were evaluated, and all data deemed relevant were included in this analysis. The clinical and scientific background was described and discussed, and the quality of evidence and level of recommendation were graded according to the Centers for Disease Control criteria.

The in vitro anti-herpes simplex virus type-1 and type-2 activity of Long Dan Xie Gan Tan, a prescription of traditional Chinese medicine

BACKGROUND

Long Dan Xie Gan Tan (LDXGT), a decoction of radix gentianae for purging the pathogenic inflammation of the liver, is a widely used prescription among many in traditional Chinese medicine. The prescription is primarily used to treat the disorders induced by damp-heat in the liver and the gall bladder.

METHODS

In this study, the in vitro anti-herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2) activity of the water extract of LDXGT was investigated.

RESULTS

LDXGT water extract was shown to exhibit anti-HSV activity. The IC(50) values of LDXGT against HSV-1 and HSV-2 infections were 257.5 +/- 12.2 and 494.6 +/- 1.8 microg/ml, respectively. It had a CC(50) value of 4,077.2 +/- 2.4 microg/ml towards Vero cells and showed no cytotoxic effect at a concentration of 2,000 microg/ml or below. The prescription was also found to inactivate HSV-2 infectivity in a dose-, time- and temperature-dependent manner.

CONCLUSIONS

In summary, the water extract of LDXGT was concluded to inhibit HSV-1 and HSV-2 infection at different magnitudes of potency, and our observations also suggested that the effect was likely mediated by directly inactivating the virus infectivity.

Foscarnet salvage therapy for acyclovir-resistant varicella zoster: report of a novel thymidine kinase mutation and review of the literature

The authors describe an acyclovir-resistant varicella zoster virus infection in a pediatric patient after hematopoietic stem cell transplant, the use of foscarnet as salvage therapy, and review the literature to clarify the pediatric experience with foscarnet in this setting. A novel thymidine kinase mutation is described, along with a new phenotypic assay for characterizing acyclovir resistance in varicella zoster virus.

The neurotropic herpes viruses: herpes simplex and varicella-zoster

Herpes simplex viruses types 1 and 2 (HSV1 and HSV2) and varicella-zoster virus (VZV) establish latent infection in dorsal root ganglia for the entire life of the host. From this reservoir they can reactivate to cause human morbidity and mortality. Although the viruses vary in the clinical disorders they cause and in their molecular structure, they share several features that affect the course of infection of the human nervous system. HSV1 is the causative agent of encephalitis, corneal blindness, and several disorders of the peripheral nervous system; HSV2 is responsible for meningoencephalitis in neonates and meningitis in adults. Reactivation of VZV, the pathogen of varicella (chickenpox), is associated with herpes zoster (shingles) and central nervous system complications such as myelitis and focal vasculopathies. We review the biological, medical, and neurological aspects of acute, latent, and reactivated infections with the neurotropic herpes viruses.

Genital herpes due to acyclovir-sensitive herpes simplex virus caused secondary and recurrent herpetic whitlows due to thymidine kinase-deficient/temperature-sensitive virus

Herpes simplex virus (HSV)-2 caused a genital ulcer in a 40-year-old allogenic stem cell recipient, and a secondary herpetic whitlow appeared during 2 months of acyclovir (ACV) therapy. Both genital ulcer, and whitlow were cured 3 months later, but 6 months after recovery the whitlow alone recurred. DNA of the genital, first, and recurrent whitlow isolates showed similar endonuclease digestion fragment profiles. The genital virus was ACV-sensitive, and the two whitlow isolates were ACV-resistant/thymidine kinase (TK)-deficient. The TK gene of the whitlow isolates had the same frame shift from the 274th amino acid and termination at the 347th amino acid due to the deletion of a cytosine at the 819th nucleotide. Because the temperature of the thumb is 33/34 degrees C or lower, the temperature sensitivity of the isolates were compared, and both whitlow isolates were significantly more temperature-sensitive (ts) at 39 degrees C than the genital isolate. The two whitlow isolates showed cutaneous pathogenicity in mouse ear pinna but not midflank, while the genital isolate was pathogenic at both sites, suggesting that temperature adaptation was an important element of pathogenicity in the whitlow. The virus populations of isolates of the genital, and first whitlow were examined by 31, and 82 clones, respectively, and the clones from genital, and whitlow isolates were ACV-sensitive, and -resistant, respectively, showing their homogeneity. The acyclovir-sensitive genital lesion had spread as a TK-deficient/ts herpetic whitlow during ACV treatment, and an apparently TK-deficient virus adapted to the local temperature might have caused the whitlow recurrence.

Oral topical cidofovir: novel route of drug delivery in a severely immunosuppressed patient with refractory multidrug-resistant herpes simplex virus infection

We present a case of serious treatment-refractory acyclovir- and foscarnet-resistant herpes simplex virus (HSV) type-1 orolingual infection that responded to oral cidofovir rinses after failure of acyclovir and foscarnet therapy. The use of 3% cidofovir in a saline rinse for refractory mucosal HSV infection appears promising but needs prospective evaluation.

DNA Polymerase Mutations in Drug-Resistant Herpes Simplex Virus Mutants Determine In Vivo Neurovirulence and Drug-Enzyme Interactions

Mutations in the thymidine kinase and DNA polymerase genes of herpes simplex virus (HSV) might confer resistance to antiviral drugs, particularly in immunocompromised patients who suffer from chronic and/or disseminated lesions. The patterns of cross-resistance and neurovirulence in mice of several DNA polymerase mutants selected under pressure of foscarnet (PFA) and different acyclic nucleoside phosphonates (ANPs), including ( S)-3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of adenine (HPMPA) and cytosine (HPMPC, cidofovir) and 2-phosphonylmethoxyethyl (PME) derivatives of adenine (PMEA) and 2,6-diaminopurine (PMEDAP), were investigated. The mutants were derived from the HSV-1 strain KOS following either single or multiple steps of selection with PFA (V714M, A719V, S724N and T821M), PMEA (S724N, L802F and R959H), PMEDAP (Q618H, S724N, S724N+D1070N), HPMPC (V573M, R700M and K960R) or HPMPA (W998L, L1007M and I1028T). These amino acid substitutions were located in different subdomains of the HSV-1 DNA polymerase, either in conserved or non-conserved regions. The sensitivity of the mutants to a new class of ANPs, the 6-(2-[phosphonomethoxy]alkoxy)pyrimidines HPMPO-DAPy and PMEO-DAPy, was investigated. Cross-resistance between the HPMP derivatives and HPMPO-DAPy, on the one hand, and between the PME derivatives and PMEO-DAPy, on the other hand, was observed. Different degrees of cross-resistance between PME derivatives, PMEO-DAPy, PFA and acyclovir were noticed. The mutants ranged from exhibiting near wild-type neurovirulence (V714M, A719V, S724N and L1007M) to significant attenuation (Q618H, S724N+D1070N, L802F, R700M, K960R, W998L and I1028T) or higher levels of attenuation (V573M). It appears that drug-resistant mutants arising under the pressure of HPMP derivatives have the lowest levels of neurovirulence.

Susceptibility of drug-resistant clinical herpes simplex virus type 1 strains to essential oils of ginger, thyme, hyssop, and sandalwood

Acyclovir-resistant clinical isolates of herpes simplex virus type 1 (HSV-1) were analyzed in vitro for their susceptibilities to essential oils of ginger, thyme, hyssop, and sandalwood. All essential oils exhibited high levels of virucidal activity against acyclovir-sensitive strain KOS and acyclovir-resistant HSV-1 clinical isolates and reduced plaque formation significantly.

Management of recurrent oral herpes simplex infections

The literature has been reviewed for evidence of the efficacy of antiviral agents in both the prophylaxis and treatment of recurrent oral herpes simplex virus (HSV) infections and discussed by a panel of experts. Emphasis was given to randomized controlled trials. Management of herpes-associated erythema multiforme and Bell palsy were also considered. The evidence suggests that 5% acyclovir (ACV) in the cream base may reduce the duration of lesions if applied early. Recurrent herpes labialis (RHL) and recurrent intraoral HSV infections can be effectively treated with systemic ACV 400 mg 3 times a day or systemic valacyclovir 500 to 1000 mg twice a day for 3 to 5 days (longer in the immunocompromised). RHL in the immunocompetent can be effectively prevented with (1) sunscreen alone (SPF 15 or above), (2) systemic ACV 400 mg 2 to 3 times a day, or (3) systemic valacyclovir 500 to 2000 mg twice a day. Valacyclovir 500 mg twice a day is also effective in suppressing erythema multiforme triggered by HSV. Further studies are needed to compare treatment efficacy between topical penciclovir, docosanol, and ACV cream for RHL.

Factors that affect in vitro measurement of the susceptibility of herpes simplex virus to nucleoside analogues

OBJECTIVES

To identify factors that contribute to variability of HSV antiviral susceptibility breakpoints.

METHODS

Acyclovir and penciclovir IC(50)'s for 12 HSV clinical isolates were measured in two laboratories using plaque reduction assay (PRA), an enzyme immunoassay (EIA)-based antigen reduction, and DNA hybridization on Vero, A549, MRC-5, HEL299 and HELG monolayers. Pair-wise comparisons were performed to evaluate variables including testing laboratory, technique, monolayer, and antiviral. The proportion of false results was analyzed using a conventional susceptibility IC(50) breakpoint of 2 microg/ml.

RESULTS

Acyclovir-resistant HSV isolates were correctly identified by all methods. In contrast, there were 6-67% of susceptible isolates incorrectly characterized as drug-resistant. Variables associated with these errors included testing site, assay method, cell line and antiviral. A549, DNA hybridization, and penciclovir were associated with the highest IC(50)'s, whereas the PRA, EIA, and human fibroblast-monolayers provided the best differentiation between susceptible and resistant HSV isolates.

CONCLUSIONS

The current recommendations to use a single discriminating value to define HSV resistance to nucleoside analogues can be problematic. False results are influenced in various degrees by the laboratory method, tissue culture and antivirals.

Oral and perioral herpes simplex virus type 1 (HSV-1) infection: review of its management

Herpes simplex virus type 1 (HSV-1) gives rise to a variety of clinical disorders and is a major cause of morbidity and mortality worldwide. HSV-1 infections are common in oral and perioral area. The aim of the present report was to critically examine the published literature to evaluate the advantages and limitations of therapy of HSV-1 infection in both immunocompetent and immunocompromised patients. Systemic antiviral therapy has been widely accepted as effective for primary herpetic gingivostomatitis. Aciclovir (ACV) 5% cream seems to be the accepted standard topical therapy for herpes labialis, being both effective and well tolerated, although penciclovir 1% cream has been proposed as a potentially useful treatment. Systemic ACV may be effective in reducing the duration of symptoms of recurrent HSV-1 infection, but the optimal timing and dose of the treatment are uncertain. Aciclovir and famciclovir may be of benefit in the acute treatment of severe HSV-1 disease in immunocompromised patients. There is also evidence that prophylactic oral ACV may reduce the frequency and severity of recurrent attack of herpetic infection in immunocompromised patients, but the optimal timing and duration of treatment is uncertain and can vary in different situations.

A Retrospective, Case-Control Study of Acyclovir Resistance in Herpes Simplex Virus

BACKGROUND

Occasional cases of acyclovir resistance have been documented in the treatment of herpes simplex virus (HSV) infection. Thirty-eight subjects with acyclovir-resistant infections were identified in an epidemiological surveillance program involving 1811 HSV-infected subjects in France.

METHODS

Twenty-three index cases from whom acyclovir-resistant HSV strains had been isolated were compared with 46 control subjects matched for immunological status. Sociodemographic characteristics, features of the acyclovir-resistant HSV episode, history of HSV infection, treatment, outcome, and immunological history were recorded.

RESULTS

Twenty-two index case patients presented with immunodepression. Sixty-five percent reported clinically manifest recurrences, compared with 33% of matched control subjects. Significantly more index case patients had used antiviral drugs, and they had used them more often than had control subjects. However, 26.1% of index case patients reported no antiviral exposure in the previous 2 years. Two-thirds of the strains recovered from the index case patients were isolated because of suspicion of clinical resistance to acyclovir.

CONCLUSIONS

Clinical treatment resistance is associated with acyclovir-resistant HSV strains, but acyclovir-resistant strains were also isolated from treatment-naive subjects.

Development of herpes simplex virus disease in patients who are receiving cidofovir

BACKGROUND

Cidofovir is a nucleotide analogue with antiviral activity against a wide range of DNA viruses, including herpes simplex virus (HSV). In vitro resistance to cidofovir has been reported with use of laboratory HSV strains; clinical failure of cidofovir therapy for HSV disease has also been reported with an isolate that was susceptible by in vitro testing.

PATIENTS AND METHODS

Three patients with HSV disease that was unresponsive to cidofovir therapy had viral isolates obtained and stored; the isolates were analyzed for antiviral susceptibility by an antigen reduction assay (ARA). PCR cloning and automated sequencing were performed for isolates that displayed in vitro resistance. Mutations were identified by comparison with the appropriate HSV consensus sequence.

RESULTS

An HSV type 2 (HSV-2) isolate recovered from patient 2 displayed in vitro cidofovir resistance with an inhibitory concentration of 50% (IC50) of 13.06 microg/mL. HSV type 1 isolates recovered from patients 1 and 3 had elevated IC50s to cidofovir (7.32 and 8.23 microg/mL, respectively); however, these isolates did not meet the cutoff point for resistance according to the ARA. Sequencing of a cidofovir-resistant HSV-2 isolate revealed several DNA polymerase mutations that had not been previously described during in vitro resistance selection.

CONCLUSIONS

To our knowledge, this is the first report of cidofovir resistance in HSV developing in vivo. The 3 sequenced clones all contained mutations truncating the pol C' end, suggesting that this region may be critical for cidofovir antiviral activity. In addition, the presence of multiple mutations suggests that the altered DNA polymerase of cidofovir-resistant virus may have introduced additional mutations into the viral genome. Introduction of the mutations identified in wild-type HSV strains is needed before the resistance phenotype can be definitively associated with any of the mutations found. Additional studies are needed to delineate the mechanisms of cidofovir resistance in HSV.

Recurrent antiviral-resistant genital herpes in an immunocompetent patient

Herpes simplex virus type 2 (HSV-2) resistance to antiviral drugs has been described primarily in immunocompromised patients. We report an apparently immunocompetent, human immunodeficiency virus-negative male patient who has experienced repeated HSV-2 genital outbreaks despite receiving antiviral prophylaxis with several different drugs. Several of the HSV-2 genital isolates from this patient have been confirmed as resistant to acyclovir and penciclovir. Antiviral resistance occurred in the setting of long-term prednisone treatment and intermittent acyclovir prophylaxis at suboptimal doses and persisted despite the cessation of oral steroid treatment. The patient's genital herpes outbreaks were not controlled by high-dose prophylaxis with acyclovir, valacyclovir, and famciclovir. Cessation of antiviral prophylaxis resulted in reversion of this patient's HSV-2 isolates to acyclovir and penciclovir sensitivity, although resistant virus reappeared when antiviral prophylaxis was resumed. Transmission of a sensitive HSV-2 strain from this patient to a female sex partner was observed. These observations confirm previous reports that resistance to acyclovir may develop during prophylactic therapy in an otherwise well, immunocompetent patient. These findings support the conclusion that both drug-sensitive and drug-resistant HSV-2 strains established latency in this patient and that both strains are capable of frequent reactivation.

Characterization of herpes simplex virus type 1 thymidine kinase mutants selected under a single round of high-dose brivudin

A broad variety of herpes simplex virus type 1 clones was selected under a single round of high-dose selection with brivudin. Mutations in the thymidine kinase (TK) genes consisted of 42% frameshift mutations within homopolymer repeats of G's and C's and single nucleotide substitutions (58%) that produced stop codons (Q261 and R281) or a new codon at the site of the substitution (A168T, R51W, G59W, G206R, R220H, Y239S, and T287 M). The A168T change, associated with an altered TK phenotype, proved to be the most commonly selected substitution. For the different mutants, a correlation between phenotype, genotype, and in vivo neurovirulence was observed.

Cidofovir for cytomegalovirus reactivation in pediatric patients after hematopoietic stem cell transplantation

BACKGROUND

Cidofovir (CDV) is a nucleotide analogue with broad antiviral activity. This drug has a very favorable pharmacokinetic profile that enables intermittent dosing, but the potential for nephrotoxicity has hitherto restricted its use in stem cell transplant recipients. Data on pediatric patients are limited.

OBJECTIVES

To report the efficacy and toxicity of CDV in a group of pediatric patients with cytomegalovirus (CMV) reactivation after allogeneic stem cell transplantation.

STUDY DESIGN

Prospective evaluation of safety and efficacy of CDV used pre-emptively for CMV reactivation in 10 out of 30 children who underwent allogeneic hematopoietic stem cell transplantation from January 2000 to December 2001. In all the patients but one, CDV was used as second-line therapy (after foscarnet or ganciclovir) of CMV reactivation.

RESULTS

Overall, 12 courses of CDV were administered with a median 5 doses per course, range 1-6 (two patients were treated twice). Considering the first CDV treatment episode, 8 out of 10 patients had positive CMV antigenemia assay when they started CDV. Five of eight antigenemic patients responded completely while three were switched to foscarnet or ganciclovir, respectively, due to increasing (one) or persistent CMV antigenemia (two). Overall, the therapy with CDV was well tolerated, but it was withdrawn in one patient due to a two-fold increase in the baseline creatinine level. This patient concurrently had a high tacrolimus blood level.

CONCLUSION

Safety is the major concern regarding the use of CDV but the adoption of probenicid, intravenous hydration and anti-emetic therapy improved its tolerability profile. Our data suggest that CDV has an acceptable toxicity and would deserve further controlled studies in the setting of pre-emptive therapy for CMV.

Genotypic characterization of the DNA polymerase and sensitivity to antiviral compounds of foscarnet-resistant herpes simplex virus type 1 (HSV-1) derived from a foscarnet-sensitive HSV-1 strain

Foscarnet is widely used for the treatment of acyclovir-resistant herpesvirus infections, and foscarnet-resistant herpesvirus infections are a serious concern in immunocompromised patients. Twenty-seven single-plaque isolates of herpes simplex virus type 1 (HSV-1) resistant to foscarnet were selected from foscarnet- and acyclovir-sensitive HSV-1 strain TAS by exposure to foscarnet, and the DNA polymerase genes were analyzed. The sensitivities of these mutants to foscarnet, cidofovir, S2242, acyclovir, ganciclovir, and penciclovir were determined. A single amino acid substitution, double amino acid substitutions, and a combination of a single amino acid substitution with a deletion or insertion of amino acid residues in the viral DNA polymerase were demonstrated in 21, 4, and 2 isolates, respectively. Of the 27 isolates, an amino acid substitution of serine for asparagine at amino acid position 724 in the DNA polymerase (724 S-N) was detected in 8 isolates. An amino acid substitution in conserved region II was demonstrated in these eight isolates as well as four other isolates. The mutation in the DNA polymerase responsible for resistance to foscarnet was located between the pre-IV region and conserved region V, especially within conserved region II. All the isolates were sensitive or hypersensitive to cidofovir and ganciclovir. Seven, 5, and 15 of the 27 isolates were also sensitive to S2242, acyclovir, and penciclovir, respectively. Thus, most of the foscarnet-resistant HSV-1 isolates were sensitive or hypersensitive to cidofovir and ganciclovir.

Survey of acyclovir-resistant herpes simplex virus in the Netherlands: prevalence and characterization

BACKGROUND

Widespread and frequent use of acyclovir (ACV) for treatment, suppressive therapy and prophylaxis of herpes simplex virus (HSV) infections and its over the counter availability may be associated with emergence of HSV resistance.

OBJECTIVES

To determine the prevalence of ACV-resistant HSV isolates in different patient groups between 1999 and 2002 in the Netherlands.

STUDY DESIGN

A total of 542 isolates, 410 HSV-1 and 132 HSV-2, from 496 patients were screened for reduced susceptibility to ACV. A newly developed ELVIRA HSV screening assay was used that allowed a high throughput screening. The genotypic analysis of the HSV thymidine kinase gene was performed to identify resistance-associated mutations.

RESULTS

Thirteen isolates, 8 HSV-1 and 5 HSV-2, from 10 patients (2%) were found resistant to ACV. A single ACV-resistant strain was identified among isolates from 368 immunocompetent patients (0.27%; 95% confidence interval [CI], 0.007%-1.5%), whereas in nine isolates from 128 immunocompromised patients resistant HSV was identified (7%; 95% CI, 3.26%-12.93%). The highest frequency of ACV-resistant HSV was associated with bone marrow transplantation: four patients out of 28 (14.3%) shed resistant virus. In addition, resistant virus was obtained from two HIV-positive patients, one patient with a hematological malignancy and two patients on immunosuppressive drugs. Further testing showed that none of the isolates was resistant to foscarnet. Several new mutations were identified in the thymidine kinase gene of these resistant isolates, and their effect on ACV-resistance is discussed.

CONCLUSIONS

Our study shows that the prevalence of ACV resistance is low in immunocompetent patients (0.27%), whereas ACV-resistant HSV infections occur relatively frequently in immunocompromised patients (7%; P < 0.0001). This emphasizes the need for drug susceptibility monitoring of HSV infections in immunocompromised patients with persisting infections despite antiviral therapy.

Resistance of Herpes Simplex Virus Infections to Nucleoside Analogues in HIV‐Infected Patients

Antiviral treatment of herpes simplex virus (HSV) infections with nucleoside analogues has been well established for >2 decades, but isolation of drug-resistant HSV from immunocompetent patients has remained infrequent (0.1%-0.7% of isolates) during this period. Even when drug-resistant HSV is isolated from an immunocompetent patient, this virus, with rare exceptions, is cleared normally without adverse clinical outcome. Although drug-resistant HSV is more commonly isolated from immunocompromised patients (4%-7% of isolates) and is more likely to be clinically significant, the prevalence of drug-resistant HSV even among these patients, has been stable over the past 2 decades. Despite this stable prevalence, disease due to drug-resistant HSV remains an important problem for many immunocompromised patients, including those with HIV infection. This article reviews the prevalence, pathogenesis, and implications of drug-resistant HSV infections in HIV-infected patients.

Combating infections in hematopoietic stem cell transplant recipients

Infections with a diverse group of microorganisms remain the leading causes of morbidity and mortality after hematopoietic stem cell transplantation. Importantly, the epidemiology of infectious complications has shifted substantially with changes in antimicrobial prophylaxis, conditioning regimens and graft manipulation, such that invasive mould infections and late viral infections are now the over-riding concerns. New antivirals and antifungals have entered clinical practice and hold considerable promise for improved outcomes.

HSV excretion after bone marrow transplantation: a 4-year survey

BACKGROUND

Herpes simplex virus (HSV) oral excretions are common after bone marrow transplantation (BMT).

OBJECTIVE

We report a 4-year systematic survey of HSV excretions in an adult population who underwent BMT (289 transplantations).

STUDY DESIGN

Patients received either intravenous ACV treatment when mucositis occurred or systematic intravenous ACV prophylaxis from initiation of the BMT conditioning until the end of aplasia. All patients were followed up for HSV excretions.

RESULTS

Twenty-eight patients (9.7%) excreted HSV. The occurrence of HSV excretions was similar in both allogeneic and autologous transplant patients. The incidence was significantly lower when ACV was systematically used after transplantation (2.5%) compared to when ACV was implemented for mucositis (12%). ACV-resistant HSV was detected in three patients who received allogeneic transplantation, representing 27% of allogeneic recipients excreting HSV.

CONCLUSION

HSV infection prophylaxis with high dose of intravenous ACV resulted in a decreased incidence of HSV excretion. Nevertheless, the risk of emergence of ACV resistance, especially among allogeneic transplant patients, appears to be identical whatever the route and dose of ACV prophylaxis.

ELVIRA HSV, a yield reduction assay for rapid herpes simplex virus susceptibility testing

A colorimetric yield reduction assay, ELVIRA (enzyme-linked virus inhibitor reporter assay) HSV, was developed to determine the antiviral drug susceptibilities of herpes simplex virus (HSV). It uses an HSV-inducible reporter cell line. This simple and rapid assay has an objective readout, low inoculum size, and good reproducibility. The results correlate well with those of the plaque reduction assay.

Herpes simplex virus: an occupational hazard in dentistry

Approximately 70% of the population in the western world become infected with the herpes simplex virus type 1 (HSV-1) by the second decade of life. This review discusses the role of the HSV-1 as a potential occupational hazard for dental workers, focusing on herpes labialis, herpetic whitlow and keratitis. The risks associated with the dental treatment of patients with HSV-1, both from the perspective of the clinician and the patient are presented. Procedures for minimising the impact of HSV-1 within the dental practice, in particular infection control, delivery of treatment and patient education, are addressed. The management options for recurrent herpes labialis are also reviewed.

Genotypic and Phenotypic Characterization of Acyclovir-Resistant Herpes Simplex Viruses Isolated from Haematopoietic Stem Cell Transplant Recipients

Thirty-one herpes simplex virus type one (HSV-1) isolates from 12 haematopoietic stem cell transplant recipients with persistent HSV infections despite acyclovir (ACV) prophylaxis or treatment, were genotypically and phenotypically characterized. The relationship between drug susceptibility of the isolates and mutations in thymidine kinase (TK) and DNA polymerase (DNA pol) genes was examined. In all 12 patients, HSV infections were due to ACV-resistant, foscarnet-sensitive viruses. Out of 31 isolates examined, 23 were resistant and eight were sensitive to ACV; eight patients carried viruses with frameshift mutations in the TK gene (due to addition or deletion of single nucleotides in homopolymeric repeats). These mutations were found at codon 61 (G deletion, one patient), 146 (G insertion, five patients) and 153 or 185 (C deletion, one patient each). In four patients, viruses were selected during ACV therapy that contained novel amino acid substitutions in the TK gene (H58R, G129D, A189V, R216H, R220C). Their possible role in ACV resistance was further confirmed phenotypically and by the absence of any resistance-associated mutations in the DNA pol gene. These substitutions were located in ATP- or nucleoside-binding sites or in conserved regions of the TK gene. In addition, a single mutation, Q570R, in the δ-region C of the DNA pol gene, was identified in an isolate from a single patient with resistance to ACV. Our study confirms and expands previous data on genotypic changes associated with ACV resistance of HSV-1 clinical isolates.

Surveillance network for herpes simplex virus resistance to antiviral drugs: 3-year follow-up

Herpes simplex virus (HSV) infections are very common in the general population and among immunocompromised patients. Acyclovir (ACV) is an effective treatment which is widely used. We deemed it essential to conduct a wide and coordinated survey of the emergence of ACV-resistant HSV strains. We have formed a network of 15 virology laboratories which have isolated and identified, between May 1999 and April 2002, HSV type 1 (HSV-1) and HSV-2 strains among hospitalized subjects. The sensitivity of each isolate to ACV was evaluated by a colorimetric test (C. Danve, F. Morfin, D. Thouvenot, and M. Aymard, J. Virol. Methods 105:207-217, 2002). During this study, 3900 isolated strains among 3357 patients were collected; 55% of the patients were immunocompetent. Only six immunocompetent patients excreted ACV-resistant HSV strains (0.32%), including one female patient not treated with ACV who was infected primary by an ACV-resistant strain. Among the 54 immunocompromised patients from whom ACV-resistant HSV strains were isolated (3.5%), the bone marrow transplantation patients showed the highest prevalence of resistance (10.9%), whereas among patients infected by human immunodeficiency virus, the prevalence was 4.2%. In 38% of the cases, the patients who excreted the ACV-resistant strains were treated with foscarnet (PFA), and 61% of them developed resistance to PFA. The collection of a large number of isolates enabled an evaluation of the prevalence of resistance of HSV strains to antiviral drugs to be made. This prevalence has remained stable over the last 10 years, as much among immunocompetent patients as among immunocompromised patients.

Molecular analysis of clinical isolates of acyclovir resistant herpes simplex virus

We characterised the antiviral phenotype and genotype of 41 herpes simplex virus (HSV) strains from patients clinically resistant to acyclovir (ACV). Our results confirm recognised mutational sites as being major determinants of thymidine kinase (tk)-associated ACV resistance, in particular insertions and/or deletions at homopolymer stretches of Gs and Cs (59% of all isolates). Previously described amino acid substitutions in functional sites of the tk were also identified (7% of all isolates). In addition, we identified several stop codons in novel locations on the amino acid sequence (7% of all isolates) and amino acid substitutions (15% of all isolates) likely to be directly responsible for conferring resistance to ACV. When there were no mutations detected in the tk gene (12% of all isolates), mutations in the DNA polymerase gene likely to be important in the generation of resistant virus were identified.

Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates HPMPC (cidofovir), PMEA (adefovir), and PMPA (tenofovir) have proved to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections: cidofovir against herpesvirus (herpes simplex virus types 1 and 2 varicella-zoster virus, cytomegalovirus [CMV], Epstein-Barr virus, and human herpesviruses 6, 7, and 8), polyomavirus, papillomavirus, adenovirus, and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus, and orf virus) infections; adefovir against herpesvirus, hepadnavirus (human hepatitis B virus), and retrovirus (human immunodeficiency virus types 1 [HIV-1] and 2 [HIV-2], simian immunodeficiency virus, and feline immunodeficiency virus) infections; and tenofovir against both hepadnavirus and retrovirus infections. Cidofovir (Vistide) has been officially approved for the treatment of CMV retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) has been approved for the treatment of HIV infections (i.e., AIDS), and adefovir dipivoxil (Hepsera) has been approved for the treatment of chronic hepatitis B. Nephrotoxicity is the dose-limiting side effect for cidofovir (Vistide) when used intravenously (5 mg/kg); no toxic side effects have been described for adefovir dipivoxil and tenofovir disoproxil fumarate, at the approved doses (Hepsera at 10 mg orally daily and Viread at 300 mg orally daily).

Sequential Switching of Dna Polymerase and Thymidine Kinase-Mediated Hsv-1 Drug Resistance in An Immunocompromised Child

Sequential herpes simplex virus type 1 (HSV-1) isolates were obtained from a paediatric haematopoietic stem cell transplant (HSCT) patient who received prolonged therapy with acyclovir (ACV) followed by foscarnet (PFA) and topical cidofovir (HPMPC) for severe persistent mucocutaneous HSV-1 infection. The isolates were retrospectively studied for drug resistance. The first resistant isolate associated with clinical failure of antiviral therapy emerged 44 days post-ACV treatment initiation. Susceptibility testing revealed an ACV-resistant HSV strain that demonstrated cross resistance to PFA in the absence of any previous PFA treatment. The observed cross resistance was conferred by a single amino acid substitution, Ser724Asn, in the HSV DNA polymerase (DNA pol) gene. During the subsequent course of ACV therapy, the ACV/PFA-cross-resistant isolates were replaced by ACV-resistant, PFA-sensitive isolates. These isolates carried no DNA pol mutations, but had an Arg163His substitution in the thymidine kinase gene. Upon subsequent switching of antiviral therapy from ACV to PFA, the original ACV/PFA-cross-resistant DNA pol mutant re-appeared. Our study shows the emergence of different drug-resistant HSV variants during ongoing, unchanged ACV therapy. Furthermore, a rapid re-selection of the original resistant variant was observed after switch. For optimal antiviral management of HSV infections in HSCT recipients, therapeutic decisions should be guided by drug susceptibility results whenever therapeutic failure is observed and/or when changes in antiviral treatment are considered.

Herpes simplex virus infection in adult patients after unrelated cord blood transplantation: a single-institute experience in Japan

Herpes simplex virus (HSV) infection in adult patients who underwent cord blood transplantation (CBT) from unrelated donors was studied. None of nine HSV-seronegative patients developed HSV disease after CBT. Of 28 HSV-seropositive patients, seven (25%) developed HSV disease at a median of 92 days after CBT (range, 52-239 days). The cumulative incidence of HSV disease in HSV-seropositive patients was 27% at 12 months after CBT. The manifestations of HSV disease included gingivostomatitis (three patients), herpes labialis (two patients), localized herpes facialis of the nose (one patient), and disseminated eczema herpeticum (one patient). HSV disease recurred in two patients as gingivostomatitis and disseminated eczema herpeticum. All the patients responded to antiviral therapy. The presence of grade II-IV acute graft-versus-host disease (GVHD) was significantly associated with a higher rate of HSV disease after CBT (51 vs 8%, P=0.015). These results suggest that the recovery of HSV-specific immune responses is delayed in patients who develop grade II-IV acute GVHD after CBT.

Herpes simplex virus resistance to acyclovir and penciclovir after two decades of antiviral therapy

Acyclovir, penciclovir, and their prodrugs have been widely used during the past two decades for the treatment of herpesvirus infections. In spite of the distribution of over 2.3 x 10(6) kg of these nucleoside analogues, the prevalence of acyclovir resistance in herpes simplex virus isolates from immunocompetent hosts has remained stable at approximately 0.3%. In immuncompromised patients, in whom the risk for developing resistance is much greater, the prevalence of resistant virus has also remained stable but at a higher level, typically 4 to 7%. These observations are examined in the light of characteristics of the virus, the drugs, and host factors.

A screening dye-uptake assay to evaluate in vitro susceptibility of herpes simplex virus isolates to acyclovir

The widespread use of acyclovir (ACV) could increase the prevalence of herpes simplex virus (HSV) ACV-resistant isolates, and a screening assay are thus important for routine surveillance of the ACV susceptibility of HSV. A screening dye-uptake assay was developed, based on the conventional dye-uptake assay [J. Biol. Stand. 14 (1986) 201]. The susceptibility of HSV was measured by testing two virus dilutions (10(-1) and 10(-2)) against two ACV concentrations (5 and 10 microM) on Vero cells and expressed as a reduced percentage of viral replication. The reproducibility was evaluated with HSV1 and HSV2 ACV-sensitive and ACV-resistant reference strains introduced as controls in successive series. The dye-uptake by Vero cells, the growth capacity of the HSV strains and the reduction of the viral replication in the presence of acyclovir varied by less than 14, 20 and 30%, respectively. This assay allowed the detection of a heterogenous population containing as few as 20% of ACV-resistant strain. The screening test was applied to 500 HSV isolates in a prospective study, and over 95% of the HSV isolates tested were characterised using a single test. This test appeared to be half the cost and much easier to carry out than the conventional dye-uptake assay, and consequently is well suited for large scale surveillance.