When is herpes simplex virus type 2 (HSV‑2) transmissible?

When HSV-2 Is Transmissible

HSV-2 is transmissible at any time after initial infection, including during asymptomatic periods without visible lesions, which represents the primary mode of transmission between sexual partners. 1

Transmission During Different Clinical States

Asymptomatic Viral Shedding (Highest Risk Period)

• Asymptomatic shedding is the most common mechanism of HSV-2 transmission, occurring even when no lesions or symptoms are present. 1
• Viral shedding occurs on approximately 10.8% of days in untreated infected individuals, dropping to 2.9% of days with daily suppressive antiviral therapy. 1
• The virus is shed throughout the genital tract, including areas not covered by condoms, making transmission possible during any sexual contact. 2
• Approximately 87% of HSV-2 infected individuals are unaware of their infection, leading to inadvertent transmission during these asymptomatic periods. 1

Symptomatic Outbreaks (Peak Transmission Risk)

• Transmission risk is highest during visible genital lesions or ulcers when viral loads are markedly elevated. 1
• Vesicles contain thousands of infectious viral particles that can be transmitted through direct contact. 3
• The prodromal period (tingling, burning, or pain before visible lesions appear) also represents a high-risk transmission window. 1

Primary Infection Period

• Primary HSV-2 infection (first acquisition in a seronegative person) typically has the highest viral loads and longest duration of shedding. 3
• The incubation period is 2-10 days (up to 4 weeks), during which transmission may occur. 3

Temporal Patterns of Viral Reactivation

• HSV-2 reactivation episodes are characterized by extremely rapid viral expansion within 12 hours, followed by rapid immune containment within 24 hours. 4
• Viral shedding occurs more frequently in the first 12 months after initial infection compared to established infection. 1
• Recurrences arise with variable frequency, from once every few years to several times per month, with each episode representing a transmission opportunity. 3

Critical Clinical Implications

The Asymptomatic Transmission Problem

• Most sexual transmission occurs during asymptomatic periods when no lesions are visible, making avoidance of contact during outbreaks insufficient to prevent transmission. 1
• Unrecognized virus shedding allows transmission from individuals who are unaware they are infected or not experiencing a recurrence. 5

Impact on HIV Risk

• HSV-2 infection increases HIV acquisition risk approximately 3-fold due to genital tract inflammation and enhanced viral entry points. 1
• This makes prevention of HSV-2 transmission particularly critical in at-risk populations. 1

Common Pitfalls to Avoid

• Do not counsel patients that they are only infectious during visible outbreaks—this is the most dangerous misconception about HSV-2 transmission. 1
• Do not assume that episodic antiviral treatment reduces transmission risk; only daily suppressive therapy (valacyclovir 500 mg once daily) has been shown to reduce transmission by approximately 48-50%. 1
• Do not rely solely on condom use, as HSV-2 can be shed from areas not covered by condoms, though consistent condom use does provide partial protection. 1