Acyclovir resistance in herpes simplex virus type I encephalitis: a case report

J Neurovirol. 2017 Apr;23(2):335-337. doi: 10.1007/s13365-016-0489-5. Epub 2016 Oct 27.


Acyclovir resistance is rarely seen in herpes simplex virus (HSV) type I encephalitis. Prevalence rates vary between 0.5 % in immunocompetent patients (Christophers et al. 1998; Fife et al. 1994) and 3.5-10 % in immunocompromised patients (Stranska et al. 2005). We report a 45-year-old, immunocompetent (negative HIV antigen/antibody testing), female patient, without previous illness who developed-after a febrile prodromal stage-aphasia and psychomotor slowing. Cerebral magnetic resonance imaging (cMRI) showed right temporal and insular T2-hyperintense lesions with spreading to the contralateral temporal lobe. Cerebrospinal fluid (CSF) analysis yielded lymphocytic pleocytosis and elevated protein level. Polymerase chain reaction testing for HSV type I showed a positive result in repeat lumbar puncture. HSV type I encephalitis was diagnosed and intravenous acyclovir treatment was initiated (750 mg t.i.d.). Acyclovir treatment was intensified to 1000 mg t.i.d., due to clinical deterioration, ongoing pleocytosis and progression on cMRI 5 days after initiation of antiviral therapy. In parallel, acyclovir resistance testing showed mutation of thymidine kinase gene at position A156V prompting foscarnet therapy (60 mg t.i.d.). Patient's condition improved dramatically over 2 weeks. Acyclovir resistance is rare but should be considered in case of clinical worsening of patient's condition. To our knowledge, this is the first report of acyclovir resistance in HSV type I encephalitis of an immunocompetent and previously healthy patient in Austria.

Keywords: Acyclovir resistance; Encephalitis; Foscarnet; Herpes simplex virus type I.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyclovir / therapeutic use
  • Antiviral Agents / therapeutic use*
  • Disease Progression
  • Drug Resistance, Viral / genetics
  • Drug Substitution
  • Encephalitis, Herpes Simplex / diagnostic imaging
  • Encephalitis, Herpes Simplex / drug therapy
  • Encephalitis, Herpes Simplex / etiology*
  • Encephalitis, Herpes Simplex / virology
  • Female
  • Foscarnet / therapeutic use*
  • Herpes Simplex / complications*
  • Herpes Simplex / diagnostic imaging
  • Herpes Simplex / drug therapy
  • Herpes Simplex / virology
  • Herpesvirus 1, Human / drug effects
  • Herpesvirus 1, Human / genetics*
  • Herpesvirus 1, Human / pathogenicity
  • Humans
  • Leukocytosis / diagnostic imaging
  • Leukocytosis / drug therapy
  • Leukocytosis / etiology*
  • Leukocytosis / virology
  • Magnetic Resonance Imaging
  • Middle Aged
  • Temporal Lobe / diagnostic imaging
  • Temporal Lobe / drug effects
  • Temporal Lobe / virology


  • Antiviral Agents
  • Foscarnet
  • Acyclovir