Herpes simplex virus

• Comprises herpes simplex virus 1 (HSV-1) and HSV-2, which are members of the Human herpesvirus family
• Cause typical painful vesicular lesions on labia or external genitals
• Occasionally cause a viral encephalitis

Background

Microbiology

• Enveloped, double-stranded DNA virus
• HSV-1 and HSV-2 are morphologically and genetically distinct viruses
• Can be infected with both

Epidemiology

• Worldwide distribution, and only found in humans
  • Most common cause of genital lesions
  • Most common cause of acute viral encephalitis in the US, with age peaks at 5 to 30 years and over 50 years
• Spread through person-to-person contact with skin or mucosa; not spread via fomits
• HSV-1 has seroprevalence of 50-90% among Canadian adults1
  • Often acquired in childhood in Asia and Africa
  • More common in lower SES populations
• HSV-2 has seroprevalence of 15-20% in Canada1
  • More common in women than men, in HIV-infected people, and in MSM
  • May be subclinical if already infected with HSV-1

Pathophysiology

• Fusion of envelope and cell membrane is mediated by viral glycoproteins B, C, and D and host cell proteins cellular heparin sulfate, TNF receptors, and immunoglobulins
• Internal capsid is released, which makes its way to the nucleus
• Viral DNA polymerase enzyme and viral DNA helicase are targets of antivirals
• Viral DNA may remain latent in about 10% of nearby neurons, characterized by latency-associated transcripts (LATs)
  • Despite being latent, virus can still be shed in mucosa anywhere from 1/10 to 3/4 of days
• HSV-1 prefers trigeminal ganglia as well as cervical ganglia, or sacral nerve root ganglia if genital

Clinical Presentation

Primary infection

• Incubation period usually within 5 days for primary infection
• Mucocutaneous lesiosn may become secondarily infected

Orofacial infection

• Most common sites of primary infection are gingivostomatitis and pharyngitis
  • Includes lesions on hard and soft palate, gingiva, tongue, lips, and face
  • Pharyngeal lesions may be exudative or ulcerative
• May also have malaise, myalgias, anorexia or odynophagia, and cervical lymphadenopathy
• Self-resolving after 3 to 14 days
• Can cause a Bell palsy

Genital infection

• Genital lesions typically last 10 to 12 days, especially with first episode
  • Often widely spaced bilateral lesions
  • First episode often also involves fever, headache, malaise, and myalgias
  • May have pain, itching, dysuria, genital discharge, and inguinal lymphadenopathy
• May develop extragenital sites of infection, including buttock, groin, and thigh with HSV-2 and perioral area with HSV-1
  • Rarely fingers and eyes
  • Develop around 14 days into the disease, likely from autoinoculation
• HSV-2 genital infections are less severe if the person has had HSV-1
• 12-month recurrence rate is up to 90% for HSV-2 and 55% for HSV-1

Neurological complications

• These can include aseptic meningitis, transverse myelitis, and sacral radiculopathy
• Typically occur in conjunction with first episode of genital HSV-2 infection
• Aseptic meningitis
  • Mengitis is more common with HSV-2 than HSV-1
  • Often concurrent with primary genital infection, typically 3 to 12 days after start of symptoms
  • HSV-2 may also cause Mollaret's meningitis (benign recurrent lymphocytic meningitis)
• Autonomic dysfunction
  • May have hyperesthesia or anaesthesia of perineum, lumbar or sacrum, as well as urinary retention and constipation
  • Resolves over 4 to 8 weeks
• Transverse myelitis
  • Decreased strength and deep tendon reflexes in lower extremities in conjunction with autonomic dysfunction (as above)

Pelvic inflammatory disease

• Rare cause of PID, possibly representing dual infection with a typical bacterial copathogen

Disseminated disease

• Rarely can disseminate
• Can be cutaneous, with concurrent meningitis, hepatitis, and pneumonitis
• Can also involve monocular arthritis, thrombocytopenia, adrenal necrosis, and myoglobinuria
• Patient factors include primary genital HSV in pregnancy, reactivation of genital HSV in a patient with cellular immunocompromise

Reactivation

• Typically localized to a single mucocutaneous area
• Symptoms are usually more minor than first-episode or primary infection, and include itching and pain
  • Lesions may be atypical, with fissures and unusual ulcers
  • May be subclinical, with intermittent viral shedding
  • May be preceded by a prodrome of tingling up to 2 days
• Average duration of an episode of reactivation orolabial herpes is 5 days
• HSV-1 reactivates more frequently around mouth, and HSV-2 in genitals
• Frequency
  • HSV-2 reactivates on average 4 to 5 times annually, with a gradual decrease over time

Herpetic whitlow

• HSV infection of the finger, with acute onset swelling, pain, and tenderness with vesicles
• Also fever and regional lymphadenopathy
• Can be either acquired from parson-to-person exposure or through autoinoculation
• Higher rates in healtcare settins

Herpes gladiatorum

• Herpes simplex infection essentially anywhere on the body (chest, ears, face, and hands) associated with wrestling

Ocular herpes

• Keratitis, which presents with pain, blurred vision, chemosis, conjunctivitis, and corneal lesions
• May also cause blepharitis and conjunctivitis
• May cause chorioretinitis in infants and immunocompromised
• Acute necrotizing retinitis
  • Presents with painless vision loss in immunocompetent people as well as immunocompromised
  • 25% of cases are bilateral

Encephalitis

• Most commonly caused by HSV-1 (05% of cases)
• In children, it is often during primary infection
• Less clear in adults, where it may be primary, infection with a new strain, or reactivation of latent infection
• Characterized by acute onset fever and neurologic symptoms
  • Often affects temporal lobe, with behaviour changes