What is Encephalitis?
Encephalitis is irritation and swelling (inflammation) of the brain. It often coexists with inflammation of the covering of the brain and spinal cord (meningitis) and most cases are caused by viral infection.
Encephalitis ranges from mild to severe and may result in permanent neurological damage and death.
The illness resembles the flu and usually lasts for 2-3 weeks. It can vary from mild to life-threatening, and even cause death. Most people with a mild case can recover fully. Those with a more severe case can recover although they may have damage to their nervous system. This damage can be permanent.
Encephalitis is an acute infection and inflammation of the brain itself. This is in contrast to meningitis, which is an inflammation of the layers covering the brain.
Encephalitis is generally a viral illness. Viruses such as those responsible for causing cold sores, mumps, measles, and chickenpox can also cause encephalitis. A certain family of viruses, the Arboviruses are spread by insects such as mosquitoes and ticks. The equine (meaning horse), West Nile, Japanese, La Crosse, and St. Louis encephalitis viruses are all mosquito-borne. Although viruses are the most common source of infection, bacteria, fungi, and parasites can also be responsible.
What are symptoms of encephalitis?
Symptoms of encephalitis include sudden fever, headache, vomiting, visual sensitivity to light, stiff neck and back, confusion, drowsiness, clumsiness, unsteady gait, and irritability. Loss of consciousness, poor responsiveness, seizures, muscle weakness, sudden severe dementia and memory loss can also be found in patients with encephalitis.
Anyone experiencing symptoms of encephalitis should see a doctor immediately. What Causes Encephalitis?
While there are more than 100 germs known to cause encephalitis, some of the more common are:
- Enteroviruses, which live in the gut and are and spread via feces. Most of these cases are mild with no lasting effects. However, death can occur in rare, very severe cases. They are most likely to appear in summer and fall. They include echovirus, coxsackievirus, and many other viruses.
- Herpes Simplex Virus, type 1 and type 2. These viruses are responsible for more serious cases. HSV type 2 (genital herpes) is usually passed from a mother to her newborn during delivery. HSV type 1 (which causes cold sores and is carried by most adults) lies dormant in most people, but can become activated and travel to the brain by an infection or another trigger.
- Arboviruses, which are viruses spread by insects, can cause St. Louis encephalitis, Western equine encephalitis and Eastern equine encephalitis. The most common is California encephalitis, particularly the strain called La Crosse, which is found mostly in the Midwest and eastern United States. Arboviruses are most likely to appear in summer and fall.
Bacterial causes of encephalitis include mycobacterium tuberculosis (TB) and Bartonella henselae, also known as cat scratch disease because that is how it is usually transmitted.
More rarely, encephalitis can be triggered by a brain injury, a brain tumor, drug reactions, or a poison (e.g., lead poisoning), or by as a reaction to a vaccine.
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