What are the causes of Encephalitis?

By  ,  Onlymyhealth editorial team
Dec 21, 2012

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Quick Bites

  • Encephalitis is most often caused by viral infections.
  • Mostly, encephalitis is caused by enteroviruses.
  • Other causes include Lyme disease and herpes simplex encephalitis.
  • Certain age groups and weak immune system are at higher risk.

Encephalitis is most often caused by viral infections, but can also be caused by bacterial infection. The condition is classified into two types – primary and secondary. Primary encephalitis, also referred to as acute viral encephalitis, is a direct viral infection of the spinal cord and brain. Secondary encephalitis, also known as post-infective encephalitis, is a consequence of complications of a current viral infection.


encephalitis causes and risks



The causes of encephalitis are as follows.

  • Most cases of encephalitis are caused by enteroviruses, herpes simplex virus types 1 and 2, a bite from a rabid animal (rabies virus), or arboviruses. The transmission is from infected animals to humans through the bite of an infected tick, mosquito, or other blood-sucking insect.
  • Lyme disease, a bacterial infection spread by tick bite, can cause encephalitis.
  • Herpes simplex encephalitis (HSE) is another condition that can cause encephalitis.



Risk Factors

Anyone can develop encephalitis. Factors that may increase the risk of the condition are as follows

  • Age: Herpes simplex encephalitis due to herpes simplex virus type 1 can affect any age group, although more prevalent in persons under age 20 or over age 40. The virus is transmitted through contact with an infected person. The early signs include headache and fever for up to 5 days, followed by personality and behavioural changes, seizures, partial paralysis, hallucinations, and altered levels of consciousness.
  • Weak immune system: Those on immune-suppressing drugs, who have HIV or other conditions that weaken immune system are at greater risk of encephalitis.
  • Geographic regions: Geographical location is another risk factor as mosquito-borne or tick-borne viruses are common in particular geographic regions, which increase the chances of the condition.
  • Season: Mosquito- and tick-borne diseases are more common in spring, summer and early fall.




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