RESUMO
A clinical isolate of herpes simplex virus type 1 that is aciclovir resistant but neurovirulent in mice was described previously. The mutation in this virus is a double G insertion in a run of seven G residues that has been shown previously to be a mutational hotspot. Using a sensitive assay, it has been demonstrated that preparations of this virus are able to induce low but consistent levels of thymidine kinase (TK) activity. However, this activity results from a high frequency mutational event that inserts a further G into the 'G-string' motif and thus restores the TK open reading frame. Passage of this virus through the nervous system of mice results in the rapid selection of the TK-positive variant. Thus, this variant is the major component in virus reactivated from latently infected ganglia. Mutation frequency appears to be influenced by the genetic background of the virus.
Assuntos
Aciclovir/farmacologia , Antivirais/farmacologia , Herpesvirus Humano 1/efeitos dos fármacos , Herpesvirus Humano 1/patogenicidade , Sequência de Aminoácidos , Animais , Sequência de Bases , Linhagem Celular , Chlorocebus aethiops , Cricetinae , DNA Viral/genética , Farmacorresistência Viral , Mutação da Fase de Leitura , Gânglios Sensitivos/virologia , Variação Genética , Genótipo , Herpes Simples/virologia , Herpesvirus Humano 1/enzimologia , Herpesvirus Humano 1/genética , Humanos , Mutação , Fases de Leitura Aberta , Fenótipo , Biossíntese de Proteínas , Timidina Quinase/genética , Células Vero , Virulência/genéticaRESUMO
A panel of 10 clinical isolates of herpes simplex virus (HSV) deficient in the expression of thymidine kinase (TK) and phenotypically resistant to aciclovir was characterized. Sequence analysis revealed a variety of mutations in TK (nucleotide substitutions, insertions and deletions), most of which resulted in truncated TK polypeptides. In line with previous reports, the most common mutation was a single G insertion in the 'G-string' motif. One HSV-1 isolate and two HSV-2 isolates appeared to encode full-length polypeptides and, in each case, an amino acid substitution likely to be responsible for the phenotype was identified. Pathogenicity was determined using a zosteriform model of HSV infection in BALB/c mice. The majority of isolates appeared to show impaired growth at the inoculation site compared with wild-type virus. They also showed poor replication in the peripheral nervous system and little evidence of zosteriform spread. One exception was isolate 4, which had a double G insertion in the G-string but, nevertheless, exhibited zosteriform spread. These studies confirmed that TK-deficient viruses display a range of neurovirulence with respect to latency and zosteriform spread. These results are discussed in the light of previous experience with TK-deficient viruses.
Assuntos
Aciclovir/farmacologia , Antivirais/farmacologia , Simplexvirus/efeitos dos fármacos , Simplexvirus/isolamento & purificação , Animais , Sequência de Bases , Linhagem Celular , Chlorocebus aethiops , Cricetinae , DNA Viral/genética , Farmacorresistência Viral , Feminino , Genes Virais , Genótipo , Herpesvirus Humano 1/efeitos dos fármacos , Herpesvirus Humano 1/enzimologia , Herpesvirus Humano 1/genética , Herpesvirus Humano 1/isolamento & purificação , Herpesvirus Humano 2/efeitos dos fármacos , Herpesvirus Humano 2/enzimologia , Herpesvirus Humano 2/genética , Herpesvirus Humano 2/isolamento & purificação , Humanos , Camundongos , Camundongos Endogâmicos BALB C , Mutação , Fenótipo , Simplexvirus/enzimologia , Simplexvirus/genética , Timidina Quinase/genética , Células Vero , Virulência/genéticaRESUMO
BACKGROUND: Mathematical models can be used to predict the emergence and transmission of antiviral resistance. Previously it has been predicted that high usage of antivirals (in immunocompetent populations) to treat Herpes Simplex Virus type 2 (HSV-2) would only lead to fairly low levels of antiviral resistance. The HSV-2 predictions were based upon the assumption that drug-resistant strains of HSV-2 would be less infectious than drug-sensitive strains but that the drug-resistant strains would not be impaired in their ability to reactivate. Recent data suggest that some drug-resistant strains of HSV-2 are likely to be impaired in their ability to reactivate. OBJECTIVES: (1) To predict the effect of a high usage of antivirals on the prevalence of drug-resistant HSV-2 under the assumption that drug-resistant strains will be less infectious than drug-sensitive strains of HSV-2 and also have an impaired ability to reactivate. (2) To compare predictions with previous published predictions. METHODS: We generated theoretical drug-resistant HSV-2 strains that were attenuated (in comparison with drug-sensitive strains) in both infectivity and ability to reactivate. We then used a transmission model to predict the emergence and transmission of drug-resistant HSV-2 in the immunocompetent population assuming a high usage of antivirals. RESULTS: Our predictions are an order of magnitude lower than previous predictions; we predict that even after 25 years of high antiviral usage only 5 out of 10,000 immunocompetent individuals will be shedding drug-resistant virus. Furthermore, after 25 years, 52 cases of HSV-2 would have been prevented for each prevalent case of drug-resistant HSV-2. CONCLUSIONS: The predicted levels of drug-resistant HSV-2 for the immunocompetent population are so low that it seems unlikely that cases of drug-resistant HSV-2 will be detected.
