What is the primary mode of transmission for herpes simplex and how can it be prevented?

Transmission of Herpes Simplex Virus

Primary Mode of Transmission

Herpes simplex virus (HSV) is transmitted primarily through direct contact with infected oral secretions, skin lesions, or genital fluids during both symptomatic and asymptomatic viral shedding periods. 1

Transmission Routes by HSV Type

HSV-1 Transmission

• Orolabial transmission occurs through direct contact with infected saliva or skin vesicles, typically acquired early in life through non-sexual contact 1, 2
• Primary infections result from contact with contaminated saliva during periods of viral shedding, even when lesions are not visible 3, 2
• Transmission can occur via fomites (contaminated objects) and during medical-dental procedures, though less commonly 4

HSV-2 Transmission

• Genital herpes transmission occurs predominantly through sexual contact with infected genital fluids or mucosal surfaces 1, 5
• The highest transmission risk (30-50%) occurs when infants are born to women with primary HSV infection during delivery 1
• Transmission risk is much lower (0-5%) for infants born to women with reactivated infection 1
• Approximately 70% of HIV-infected persons are HSV-2 seropositive, highlighting sexual transmission patterns 1

Critical Transmission Characteristics

Asymptomatic Shedding

• Most genital herpes infections are transmitted by persons who are unaware they have the infection or are asymptomatic when transmission occurs 1, 6
• Only 9% of HSV-2-seropositive persons report knowing they have genital herpes 1
• Approximately 85% of healthy or HIV-infected adults shed HHV-6 intermittently in their saliva 1
• Frequent asymptomatic shedding and unrecognized symptomatic cases are the primary sources of continued HSV-2 transmission 6

Recurrent Infections

• Latent virus harbored in sensory nerve ganglia reactivates throughout life, producing infectious recurrent disease that can be symptomatic or asymptomatic 2, 4
• Recurrent infections occur at relatively short intervals along the same dermatome as the primary infection 2

Prevention Strategies

Behavioral Measures

• HIV-infected persons and all sexually active individuals should use latex condoms during every act of sexual intercourse to reduce HSV exposure risk 1, 7
• Avoid sexual contact when herpetic lesions (genital or orolabial) are evident 1, 7
• Avoid intimate contact when herpes lesions are visible 7

Medical Interventions

• Suppressive antiviral therapy with oral acyclovir, valacyclovir, or famciclovir reduces subclinical viral shedding but does not eliminate it 1
• Daily suppressive therapy should be discussed with every HSV-2-infected patient, particularly those with frequent or severe recurrences 1
• Cesarean delivery is recommended for women with genital herpes prodrome or visible HSV genital lesions at onset of labor 1

Neonatal Prevention

• Prolonged rupture of membranes (>6 hours) increases HSV transmission risk to infants, likely due to ascending infection from the cervix 1
• Cesarean delivery substantially lowers transmission risk when maternal genital shedding is present at delivery 1
• Maternal HSV antibody status before delivery influences both severity and likelihood of transmission to the infant 1

Important Clinical Caveats

Post-Exposure Prophylaxis Limitations

• Post-exposure antiviral prophylaxis is NOT indicated for preventing initial episodes of HSV infection, even when contact occurred 24 hours before lesion appearance 7
• There is no evidence supporting antiviral medications as pre-exposure or post-exposure prophylaxis to prevent HSV acquisition 7
• Transmission during asymptomatic viral shedding makes post-exposure prophylaxis impractical and of unproven efficacy 7

Diagnostic Considerations

• Diagnosis should be confirmed by sensitive diagnostic tests such as viral culture or HSV type-specific serologic tests 1
• Accurate type-specific assays rely on detection of antibodies to HSV-specific glycoprotein G1 and G2 1
• Negative laboratory results do not always indicate lack of infection due to imperfect tests 6

Special Populations

• Women infected with HIV, particularly those with low CD4+ cell counts, shed HSV from vulva and cervix more commonly than HIV-uninfected women, with most shedding being asymptomatic 1
• Maternal genital herpes is a risk factor for perinatal mother-to-child HIV transmission 1
• Increased sexual promiscuity and advanced sexual techniques contribute to rising prevalence of genital HSV infections 5