• Can be caused by all the same infections listed above
  • Up to 60% go undiagnosed
  • Thousands of cases are reported each year, but more may be occurring but symptoms may be mild or non-existent.

Most cases of encephalitis are caused by:

  • enteroviruses
  • herpes simplex virus type 1 & 2
  • Rabies (bite not required – just exposure to bats)
  • arboviruses such as West Nile Virus (transmitted form animals through tick or mosquitoes)

(Lyme disease – a bacterial infection spread by tick bite more typically causes meningitis; rarely encephalitis)

Herpes Simplex Encephalitis (HSE)

  • about 10% of cases of encephalitis
  • More than half are fatal if untreated
  • Approx. 30% result from initial infection with hepes simplex virus – the majority are reactivation of an earlier infection.
  • Most people acquire herpes simplex type 1 (cold sore) in  childhood – it’s ubiquitous
  • HSE can affect any age group
  • Most often 20 – 40year olds
  • HSV-1 Encephalitis is more common in adults
  • HSV-2 Encephalitis is more common in children
  • Rapidly progressing disease

Typical Clinical Course:

  • Classic triad is:
    1. Fever
    2. Headache
    3. Altered level of consciousness
  • Headache and fevers for five days
  • Personality change and behavioural change
  • seizures
  • hallucinations
  • altered level of consciousness
  • brain damage in adults and children beyond the neonatal period is usually seen in the frontal (leading to behavioural change and personality change) and temporal (leading to memory and speech problems) and can be severe.