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Herpes Simplex Virus for USMLE Step 2

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Herpes Simplex Virus for the USMLE Step 2 Exam
  • Etiology:
    • Caused by herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), both double-stranded DNA viruses in the Herpesviridae family.
    • HSV-1: Typically associated with orolabial infections but can cause genital infections.
    • HSV-2: Primarily responsible for genital herpes, although it may occasionally cause oral infections.
  • Epidemiology:
    • HSV-1 is commonly acquired during childhood through non-sexual contact, while HSV-2 is most often acquired in sexually active adults.
Pathophysiology
  • Latency and Reactivation:
    • Following primary infection, HSV enters sensory neurons and establishes latency in sensory ganglia (trigeminal ganglion for HSV-1, sacral ganglia for HSV-2).
    • Reactivation can be triggered by factors like stress, immunosuppression, UV light exposure, and hormonal changes.
  • Transmission:
    • Spread occurs via direct contact with infected secretions or mucosal surfaces, with asymptomatic viral shedding contributing significantly to transmission.
Clinical Manifestations
Primary HSV Infection
    • Systemic Symptoms: Typically more severe than recurrent infections and may include fever, malaise, and lymphadenopathy.
    • Orolabial HSV-1:
    • Painful vesicles or ulcers on lips, oral mucosa, or perioral skin. Gingivostomatitis is common in children during primary infection.
hsv
    • Genital HSV-2:
    • Painful vesicles and ulcers on genital or perianal skin, often accompanied by dysuria and inguinal lymphadenopathy.
Recurrent HSV Infection
    • Orolabial HSV-1 Recurrence:
    • Presents as cold sores on or around the lips, often preceded by tingling or itching.
    • Genital HSV-2 Recurrence:
    • Milder and shorter duration than primary infections, with lesions often preceded by prodromal symptoms.
Complications
    • Herpetic Whitlow:
    • HSV infection of the finger, common in healthcare workers or individuals with frequent contact with oral secretions.
    • Herpes Simplex Keratitis:
    • Infection of the cornea by HSV-1, causing dendritic ulcers and potential vision loss if untreated.
    • HSV Encephalitis:
    • Typically HSV-1, affecting the temporal lobes and presenting with fever, altered mental status, and seizures.
    • Neonatal Herpes:
    • Transmitted during delivery from mothers with active lesions, leading to disseminated infection, CNS disease, or localized skin/eye/mouth lesions.
Diagnosis
  • Polymerase Chain Reaction (PCR):
    • The preferred diagnostic method for HSV, especially for CNS infections and genital lesions, due to high sensitivity.
  • Viral Culture:
    • Useful in early lesion stages but less sensitive than PCR.
  • Serology:
    • Detects antibodies to HSV-1 and HSV-2, which is useful for identifying prior infection, but not for acute diagnosis.
Treatment
Antiviral Therapy
    • Acyclovir, Valacyclovir, and Famciclovir:
    • First-line agents effective for HSV, reducing symptom severity and recurrence.
    • Primary Episode:
    • Acyclovir: 400 mg PO three times daily for 7–10 days.
    • Valacyclovir: 1 g PO twice daily for 7–10 days.
    • Recurrent Episode:
    • Acyclovir: 400 mg PO three times daily for 5 days.
    • Valacyclovir: 500 mg PO twice daily for 3 days.
    • Chronic Suppressive Therapy:
    • For frequent recurrences (>6/year) or to reduce transmission.
    • Acyclovir: 400 mg PO twice daily.
    • Valacyclovir: 500 mg or 1 g PO once daily.
Management of Complications
    • HSV Encephalitis: Requires high-dose IV acyclovir (10 mg/kg every 8 hours for 14–21 days).
    • Neonatal Herpes: Treated with IV acyclovir (20 mg/kg every 8 hours) for 14–21 days, depending on disease severity.
    • Herpetic Keratitis: Managed with topical antiviral agents (e.g., trifluridine) or oral antivirals; ophthalmology referral is recommended.
Prevention and Reduction of Transmission
    • Condom Use: Reduces risk but does not fully prevent transmission.
    • Partner Notification: Essential for reducing spread, and suppressive therapy can reduce but not eliminate transmission risk.
    • Cesarean Delivery: Recommended for pregnant women with active genital lesions at labor to prevent neonatal transmission.
Key Points
  • HSV-1 usually causes orolabial infections, and HSV-2 typically causes genital infections, but each virus can infect either region.
  • Latency and Reactivation: HSV establishes latency in sensory ganglia, with reactivation triggered by stress or immune changes.
  • Diagnosis is confirmed by PCR for CNS and genital infections; serology is useful in identifying past exposure.
  • Antiviral Therapy: Includes acyclovir, valacyclovir, and famciclovir, which help reduce symptoms and prevent recurrences.
  • Prevention: Condom use, partner notification, and cesarean delivery in active maternal infection cases reduce the transmission risk.