What are the causes and effects of Herpes 1 (Herpes Simplex Virus Type 1)?

Causes and Effects of Herpes Simplex Virus Type 1 (HSV-1)

HSV-1 is primarily acquired through close non-sexual contact with infected persons during childhood, typically causing infections above the neck (orolabial herpes), but can also cause genital herpes through oro-genital sexual practices. 1

Transmission and Acquisition

• Primary mode of transmission: Direct contact with infected lesions or body fluids 1
• Common transmission routes:
  • Close non-sexual contact in childhood (traditional route for HSV-1) 1
  • Oro-genital sexual practices (leading to genital HSV-1 infections) 2, 1
  • Kissing (particularly for adults not infected in childhood) 3
• Incubation period: 2-10 days (can extend up to 4 weeks) 2, 1

Pathophysiology of HSV-1 Infection

HSV-1 follows a distinct pattern after initial infection:

1. Primary infection: Occurs when a person without antibodies against HSV acquires the virus for the first time 1
2. Latency establishment: The virus travels to and establishes latency in:
   • Cervical ganglia (typical for HSV-1) 2, 1
   • Trigeminal ganglia (during lip infections) 4
   • Brain tissue (demonstrated in animal models without obvious neurological signs) 4
3. Recurrent infections: Periodic reactivations of the latent virus 1

Triggers for HSV-1 Recurrence

Common factors that can trigger reactivation include:

• Psychological stress 1
• Fever 1
• Local trauma 1
• Immunosuppression 1
• UV radiation (particularly for cold sores) 1

Clinical Manifestations of HSV-1

Primary Infection

• Children: Often asymptomatic or presents as mild febrile illness 3
• Symptomatic primary infection:
  • Mucocutaneous vesicular eruptions after incubation period 5
  • Herpetic gingivostomatitis affecting tongue, lips, gingiva, buccal mucosa, hard and soft palate 5
  • Can be severe in adults not previously infected 3

Recurrent Infections

• Herpes labialis (cold sores):

  • Most common clinical manifestation 6
  • Vesiculo-ulcerative lesions at mucocutaneous junctions, particularly the lips 5
  • Progression: localized redness → papular rash → vesicular lesions → ulcers → crusting → healing 1
  • Episodes usually last less than 10 days without treatment 1

• Recurrent oral HSV-1: Uncommon in healthy individuals but can be extensive in immunocompromised patients 5

Complications of HSV-1 Infection

While generally benign, HSV-1 can cause significant complications:

• Rare complications of primary infection:

  • Widespread involvement in atopic eczema (potentially life-threatening) 7
  • Encephalitis (potentially life-threatening) 7
  • Keratoconjunctivitis 7
  • Pharyngitis 7
  • Hepatitis 7

• Complications of recurrent infections:

  • Recurrent erythema multiforme (associated with preceding herpes labialis in 65% of cases) 7
  • Psychological impact due to visible lesions and stigma 1, 6

Diagnosis

• Clinical diagnosis is often sufficient for typical presentations 5
• Laboratory confirmation recommended for atypical presentations using:
  • Viral culture
  • HSV DNA PCR
  • Antigen detection for active lesions
  • Type-specific serologic testing when no lesions are present 1

Treatment Options

• Antiviral medications:

  • Reduce duration and severity of recurrences 1
  • Options include acyclovir, valacyclovir, and famciclovir 1, 8
  • Most effective when initiated within 6 hours of symptom onset 1
  • For frequent recurrences (≥6 episodes/year), suppressive therapy should be considered 1

• Common side effects of acyclovir:

  • Short-term: nausea/vomiting (2.7%) 8
  • Long-term: nausea (4.8%), diarrhea (2.4%) 8

Prevention

• Avoid sexual contact during active outbreaks 1
• Use condoms to reduce transmission risk 1
• Consider suppressive antiviral therapy for frequent recurrences 1
• Prevent contamination of others through proper hygiene 6

Important Clinical Considerations

• Many people infected with HSV-1 are unaware they have it, contributing to transmission 1
• HSV-1 genital infections are increasing due to changing sexual practices 2, 1
• People with genital herpes due to HSV-2 have a higher risk of acquiring HIV infection 1
• Most primary and recurrent HSV-1 infections require minimal intervention, but systemic acyclovir is indicated for complicated cases 7