What is the difference between Herpes Simplex Virus 1 (HSV1) and Herpes Simplex Virus 2 (HSV2)?

Differences Between HSV-1 and HSV-2

HSV-1 and HSV-2 differ primarily in their typical anatomical site preferences, recurrence patterns, and transmission routes, though both can cause similar clinical manifestations in either oral or genital regions.

Anatomical Preferences and Epidemiology

• HSV-1 traditionally manifests above the neck (orolabial herpes), while HSV-2 typically affects areas below the waist (genital herpes), though this distinction is not absolute due to oro-genital sexual practices 1
• HSV-1 has a higher prevalence (approximately 47.8% of US population aged 14-49), compared to HSV-2 (12.1% of the same population) 1
• Women are more likely than men to acquire HSV-2 and to experience symptomatic infection 2

Clinical Manifestations

• Orolabial herpes (typically HSV-1):

  • Presents with a sensory prodrome followed by lesion evolution from papule to vesicle, ulcer, and crust stages on the lips 1
  • Untreated episodes last 7-10 days with recurrences 1-12 times per year 1
  • Can be triggered by sunlight or physiologic stress 1

• Genital herpes (typically HSV-2):

  • Similar lesion appearance and evolution to orolabial herpes 1
  • Often accompanied by local symptoms including pain, pruritis, dysuria, vaginal/urethral discharge, and inguinal lymphadenopathy (particularly in primary infection) 1
  • Most cases (80-90%) progress subclinically but may become symptomatic at any time 1

Recurrence Patterns

• HSV-2 recurs much more frequently in the genital area than HSV-1 1
• The monthly recurrence frequencies in order of frequency are: genital HSV-2 (0.33/month), oral-labial HSV-1 (0.12/month), genital HSV-1 (0.020/month), and oral HSV-2 (0.001/month) 3
• Genital herpes recurs approximately six times more frequently than oral-labial herpes, which may account for the increasing recognition of genital herpes clinically 3

Transmission and Infection

• Both viruses are transmitted through direct mucosal or cutaneo-mucosal contact 4
• The incubation period for both HSV-1 and HSV-2 is typically 2-10 days (up to 4 weeks) 1
• Prior HSV-1 infection does not reduce the rate of HSV-2 acquisition but increases the likelihood of asymptomatic HSV-2 seroconversion by 2.6 times 2
• Mixed infections with both HSV-1 and HSV-2 can occur, with studies showing higher than previously thought prevalence (27% in one study) 5, 6

Primary vs. Recurrent Infection

• Primary infection (when an HSV-seronegative person acquires HSV-1 or HSV-2) is typically the most severe manifestation 1
• In cases where a person with antibodies to HSV-1 subsequently acquires HSV-2, the genital infection is less severe but still associated with recurrences 1
• Both viruses establish latency in sensory ganglia: HSV-1 typically in the trigeminal ganglia and HSV-2 in the sacral ganglia 1, 3

Diagnostic Considerations

• Laboratory confirmation is essential as clinical diagnosis alone has poor sensitivity and specificity 1
• Recommended diagnostic methods include viral culture, HSV DNA PCR, HSV antigen detection, and type-specific serologic assays 1
• Type determination is important as it helps predict recurrence patterns and guide counseling 1

Clinical Implications

• HSV-2 is a risk factor for HIV acquisition and HSV-2 reactivation can increase HIV RNA levels in coinfected patients 1
• Neonatal herpes and increased risk for acquiring HIV are the most serious complications of genital herpes infections 1
• Both infections are lifelong, with the virus remaining in a non-multiplying episomal form in neural ganglia during latency periods 1