Significance of amino acid substitutions in the thymidine kinase gene of herpes simplex virus type 1 for resistance
ABSTRACT The analysis of the viral thymidine kinase (TK) genotype is of rising significance for testing resistance of herpes simplex virus (HSV) to antivirals especially acyclovir. However, numerous of the described amino acid (aa) substitutions are diagnostically less conclusive because of the pronounced natural polymorphism of this gene. In this study, several aa substitutions in the TK sequence of HSV-1 with unclear significance for resistance were analyzed by expression of recombinant TK proteins and determination of enzymatic activity on the basis of an enzyme linked immunosorbent assay using bromodeoxyuridine (BrdU) as TK substrate. The recombinant TK wild-type protein resulted in high TK activity and TK mutant with stop of translation showed negative results. The recombinant TK proteins containing the aa substitutions R41H or V348I had high phosphorylation activities suggesting most likely natural gene polymorphisms. By contrast, the aa changes Y53H, L139V, R163H, L298A and L315S were accompanied by negative or weakly positive TK activities indicating resistance association. In conclusion, the combination of methods described here represents a useful tool to evaluate the significance of aa substitutions for resistance of clinical HSV-1 strains.
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ABSTRACT: Since the type of herpes simplex virus (HSV) infection affects prognosis and subsequent counseling, type-specific testing to distinguish HSV-1 from HSV-2 is always recommended. Although PCR has been the diagnostic standard method for HSV infections of the central nervous system, until now viral culture has been the test of choice for HSV genital infection. However, HSV PCR, with its consistently and substantially higher rate of HSV detection, could replace viral culture as the gold standard for the diagnosis of genital herpes in people with active mucocutaneous lesions, regardless of anatomic location or viral type. Alternatively, antigen detection--an immunofluorescence test or enzyme immunoassay from samples from symptomatic patients--could be employed, but HSV type determination is of importance. Type-specific serology based on glycoprotein G should be used for detecting asymptomatic individuals but widespread screening for HSV antibodies is not recommended. In conclusion, rapid and accurate laboratory diagnosis of HSV is now become a necessity, given the difficulty in making the clinical diagnosis of HSV, the growing worldwide prevalence of genital herpes and the availability of effective antiviral therapy.Virology Journal 05/2014; 11(1):83. DOI:10.1186/1743-422X-11-83 · 2.09 Impact Factor
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ABSTRACT: The widespread use of acyclovir (ACV) and the increasing number of immunocompromised patients have raised concern about an increase in ACV-resistant Herpes Simplex Virus (HSV). ACV resistance has traditionally been a major concern for immunocompromised patients with a frequency reported between 2.5-10%. The aim of this study was to reassess the status of HSV resistance to ACV in immunocompetent and immunocompromised patients over a ten year period, between 2002-2011. This was done by retrospectively following 1425 patients. In immunocompetent patients, prevalence of resistance did not exceed 0.5% during the study period; whereas in immunocompromised patients, a significant increase was observed, rising from 3.8% between 2002-2006 (7/182 patients) to 15.7% between 2007-2011 (28/178) (p=0.0001). This sharp rise in resistance may largely be represented by allogeneic hematopoietic stem cell transplant patients, in which the prevalence of ACV resistance rose similarly from 14.3% (4/28) between 2002-2006 to 46.5% (26/56) between 2007-2011 (p=0.005). No increase in ACV resistance was detected in association with other types of immune deficiencies. Genotypic characterization of HSV UL23 thymidine kinase and UL30 DNA polymerase genes revealed 11 and 7 previously unreported substitutions, respectively. These substitutions may be related to potential polymorphisms, drug resistance, or other mutations of unclear significance.Antiviral Research 11/2014; 111. DOI:10.1016/j.antiviral.2014.08.013 · 3.43 Impact Factor
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ABSTRACT: SUMMARY The discovery of acyclovir (ACV), a nucleoside analogue, more than 30 years ago, represents a milestone in the management of HSV and VZV infections. The modest activity of ACV against CMV prompted the development of another nucleoside analogue, ganciclovir, for the management of systemic and organ-specific CMV diseases. Second-line agents such as the pyrophosphate analogue foscarnet and the nucleotide analogue cidofovir have been approved subsequently. In contrast to ACV and ganciclovir, the latter drugs do not require selective phosphorylation by viral protein kinases to be converted into their active forms. Since the introduction of these antivirals, the emergence of drug-resistant mutants has been constantly reported particularly in severely immunocompromised patients such as bone marrow and solid organ transplant recipients as well as HIV-infected individuals. In this manuscript, we discuss the characteristics of the antiviral agents currently approved for the management of HSV, VZV and CMV diseases. In recent years, the resistance of CMV to antiviral drugs has been extensively reviewed. The emergence of antiviral drug resistance is also observed with other members of the Herpesviridae family, namely HSV-1, HSV-2, VZV and HHV-6, which are the focus of this review. More specifically, we describe the laboratory methods for assessing drug susceptibilities, the frequency and clinical significance of drug-resistant infections and their management. Copyright © 2014 John Wiley & Sons, Ltd.Reviews in Medical Virology 05/2014; 24(3). DOI:10.1002/rmv.1787 · 5.76 Impact Factor