HSV-1 and HSV-2: Diagnostic Testing and Treatment
Diagnostic Testing
For active lesions, PCR testing has replaced viral culture as the gold standard for diagnosing HSV-1 and HSV-2 infections, offering consistently higher detection rates and the ability to distinguish between viral types. 1, 2
Recommended Diagnostic Approaches by Clinical Scenario
Active mucocutaneous lesions:
- PCR from lesion swab is the preferred test, with superior sensitivity compared to viral culture and the ability to type-specifically identify HSV-1 versus HSV-2 1, 2
- Direct fluorescent antibody (DFA) testing or enzyme immunoassay can be used as alternatives for symptomatic patients, though viral typing capability is essential 1
Suspected HSV encephalitis:
- PCR of cerebrospinal fluid is the diagnostic standard; the Simplexa HSV 1 & 2 Direct is the only FDA-approved device for CSF testing 3
Bloodstream infections:
- Serum is the optimal specimen type, demonstrating significantly lower cycle thresholds than whole blood (2.6 Ct bias, P < 0.001) 4
- Modified Simplexa assay in serum shows 100% positive percent agreement for HSV-1 and HSV-2 DNA detection 4
Asymptomatic individuals or when no active lesion is present:
- Type-specific serology based on glycoprotein G should be used 1, 2
- However, widespread screening for HSV antibodies is not recommended 1
- Critical caveat: Commercial serologic assays have significant limitations—HSV-1 IgG sensitivity is <85% across platforms, and the DiaSorin assay produces false-positive HSV-2 results in nearly one of every three positive tests (positive predictive value only 69.0%) 5
Treatment Regimens
First Clinical Episode of Genital Herpes (HSV-1 or HSV-2)
Valacyclovir 1 g orally twice daily for 7-10 days is the preferred first-line treatment for initial genital herpes episodes. 6, 7, 8
Alternative regimens:
- Acyclovir 400 mg orally three times daily for 7-10 days 6, 7, 8
- Acyclovir 200 mg orally five times daily for 7-10 days 9, 8
- Famciclovir 250 mg orally three times daily for 7-10 days 8
Treatment may be extended if healing is incomplete after 10 days. 6, 8
Recurrent Episodes
For recurrent genital herpes, valacyclovir 500 mg orally twice daily for 5 days is the preferred episodic therapy due to convenient dosing and proven effectiveness. 6, 8
Alternative episodic regimens:
- Acyclovir 400 mg orally three times daily for 5 days 6, 8
- Acyclovir 800 mg orally twice daily for 5 days 9, 6, 8
- Acyclovir 200 mg orally five times daily for 5 days 9, 8
- Famciclovir 125 mg orally twice daily for 5 days 6, 8
Critical timing consideration: Treatment is most effective when initiated during the prodromal period or within 24 hours of lesion onset; delayed treatment beyond 72 hours significantly reduces effectiveness. 6, 7 Patients should be provided with medication or a prescription to self-initiate at the first sign of prodrome. 6
Recurrent Herpes Labialis (Oral HSV-1)
For oral HSV-1 recurrences, initiate oral antiviral therapy during the prodrome or within 24 hours of lesion onset, as peak viral replication occurs in the first 24 hours. 7
Recommended regimens:
- Valacyclovir 500 mg orally twice daily for 5 days 7
- Acyclovir 400 mg orally three times daily for 5 days 7
- Famciclovir 125 mg orally twice daily for 5 days 7
Daily Suppressive Therapy
For patients with ≥6 recurrences per year, daily suppressive therapy reduces recurrence frequency by at least 75% and should be strongly considered. 6, 7, 8
Recommended suppressive regimens for genital herpes:
- Valacyclovir 1 g orally once daily 6, 8
- Valacyclovir 500 mg orally once daily (note: less effective in patients with ≥10 episodes per year) 9, 7, 8
- Acyclovir 400 mg orally twice daily 9, 6, 8
- Famciclovir 250 mg orally twice daily 9, 8
Recommended suppressive regimens for oral HSV-1:
- Acyclovir 400 mg orally twice daily 7
- Valacyclovir 250 mg orally twice daily 7
- Valacyclovir 500 mg orally once daily 7
Important management principles:
- Suppressive therapy significantly reduces asymptomatic viral shedding and transmission risk but does not eliminate either completely 7, 8
- After 1 year of continuous suppressive therapy, discontinue treatment to reassess recurrence frequency, as episodes often decrease over time 9, 7, 8
- Safety and efficacy documented for up to 6 years of continuous use in immunocompetent patients 7
- Antiviral resistance remains extremely low (<0.5%) in immunocompetent individuals even after prolonged use 7
Severe Disease Requiring Hospitalization
For severe HSV disease or complications (disseminated infection, pneumonitis, hepatitis, meningitis, encephalitis), acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical resolution is the recommended treatment. 9, 6, 8
For HSV encephalitis specifically: A 2026 randomized controlled trial found that adjunct dexamethasone (10 mg/kg IV four times daily for 4 days) plus aciclovir had a satisfactory safety profile but did not improve verbal memory scores compared to aciclovir alone, suggesting corticosteroids do not provide additional benefit. 10
Special Populations
HIV-infected patients:
- May require longer treatment courses and higher doses than HIV-negative patients 9, 6
- Acyclovir 400 mg orally three to five times daily until clinical resolution is recommended 9, 6
- Famciclovir 500 mg twice daily has been effective in reducing recurrences and subclinical shedding 9, 6, 8
- Critical warning: Valacyclovir in doses of 8 g per day has been associated with hemolytic uremic syndrome or thrombotic thrombocytopenic purpura in immunocompromised patients; use recommended doses only 9
Acyclovir-resistant HSV:
- Suspect resistance if lesions do not begin to resolve within 7-10 days of therapy 8
- All acyclovir-resistant strains are resistant to valacyclovir, and most are resistant to famciclovir 9
- For confirmed resistance: IV foscarnet 40 mg/kg every 8 hours is the treatment of choice 9, 8
- Alternative: Cidofovir gel for acyclovir-resistant HSV shows promise 11
Critical Clinical Pitfalls to Avoid
Topical acyclovir is substantially less effective than systemic therapy and should not be used. 9, 6, 7, 8
Do not use serologic testing to diagnose active genital lesions—positive results may reflect chronic infection, while negative results may miss recent infection. 3
Recognize that systemic antiviral drugs partially control symptoms but do not eradicate latent virus or affect subsequent recurrences after discontinuation. 9, 6, 8
Common side effects include headache (<10% of patients) and nausea (<4% of patients), with no serious adverse events documented at standard dosing in immunocompetent patients. 7, 8
No laboratory monitoring is needed for patients on episodic or suppressive therapy unless substantial renal impairment exists; for high-dose IV acyclovir, monitor renal function at initiation and once or twice weekly during treatment. 8
Transmission Prevention Counseling
Patients should be counseled that:
- Suppressive therapy reduces transmission risk to sexual partners 8
- Abstinence from sexual activity is essential when lesions or prodromal symptoms are present 7, 8
- Consistent condom use reduces HSV-2 transmission by approximately 50% 8
- Asymptomatic viral shedding occurs and transmission can occur during asymptomatic periods, though less frequently with HSV-1 than HSV-2 7
- Partners should be informed about the infection and encouraged to seek evaluation 9