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  • Brain


Encephalitis is an inflammation of the brain usually caused by infection.

What is going on in the body?

Encephalitis usually results from a viral infection of the brain tissue; however, it may be caused by a bacterial, fungal, or parasitic infection.
These tiny organisms can enter the brain tissue by any of the following routes:
  • through the bloodstream after a bite from a tick or mosquito
  • direct infection of the cells in the brain, often following a head injury
  • through the respiratory or gastrointestinal tracts where they then can travel through the bloodstream and invade the brain
  • traveling up nerves to the brain. This happens with a dormant herpes infection or after a bite from an animal with rabies.
Encephalitis may also result from the body's response to an infection, a condition referred to as post-infectious encephalitis. This condition likely occurs because of an abnormal attack on the brain by an individual's own immune system.


What are the causes and risks of the condition?

Most cases of encephalitis are caused by a viral infection of the brain tissue; however, there are numerous potential causes. Selected viruses, bacteria, fungi, parasites, and non-infectious causes of encephalitis include:
Viruses transmitted by a mosquito bite, such as:
  • West Nile virus
  • St Louis virus
  • Western equine virus
  • Eastern equine virus
  • La Crosse virus
  • Venezuelan equine virus
  • Japanese virus
Viruses transmitted by a tick bite, such as:
  • Colorado tick fever virus
  • Powassan virus
  • Far Eastern tick-borne virus
  • Central European tick-borne virus
Viruses that travel from the gut to the brain, such as:
  • Enteroviruses such as polio virus
  • Rotavirus
Viruses that travel from the lungs or upper respiratory tract to the brain, such as:
  • Influenza A virus ( this is the "flu" virus )
  • Parainfluenza virus (this is one of the common cold viruses)
  • Adenoviruses
  • Enteroviruses such as coxsackie and echoviruses
  • Varicella zoster virus ( the causes chicken pox and shingles )
  • Measles virus
  • Rubella virus ( the cause of German measles)
  • Epstein Barr virus ( the most common cause of mononucleosis )
  • Mumps virus
Viruses that start in the nerves and travel to the brain, such as:
  • Herpes Simplex viruses type 1 (most commonly diagnosed cause of viral encephalitis)
  • Rabies virus
  • Varicella zoster (rarely)
Viruses that can be sexually transmitted or result from exposure to blood, such as:
  • Human Immunodeficiency Virus (HIV) which causes AIDS
  • Hepatitis C virus
  • Herpes Simplex virus type 2 ( the cause of genital herpes)
Viruses associated with post infectious encephalitis, such as:
  • Measles virus
  • Rubella virus
  • Mumps virus
  • Varicella Zoster virus
Bacteria that are associated with encephalitis include:
  • Mycoplasma ( usually causes "walking" pneumonia )
  • Leptospira ( transmitted to humans with contact with urine, blood, or tissue from an infected animal )
  • Listeria ( usually affects pregnant women after eating tainted food )
  • Mycobacteria ( tuberculosis is caused by a bacteria in this group )
  • Treponema pallidum ( the cause of syphilis )
  • Rickettsii ( Rocky Mountain Spotted fever and Ehrlichiosis are caused by members of this family transmitted by tick bite )

Important fungal infections causing encephalitis (most commonly these occur in people with poor immune systems ) include:

  • Histoplasma ( usually a lung infection following exposure to bat droppings )
  • Cryptococcus
  • Nocardia
  • Candida
  • Coccidioides
Parasites that are associated with encephalitis include:
  • Toxoplasma ( transmitted to humans who ingest raw meat )
  • Cysticercosis ( transmitted after ingestion of the eggs of the pork tapeworm )
  • Naegleria ( usually occurs after swimming in muddy fresh water reservoirs )
  • Plasmodium ( this is the cause of malaria )
Non-infectious causes of encephalitis include:
  • Drugs ( nonsteroidal anti-inflammatory drugs such as ibuprofen, anti-seizure drugs )
  • Connective tissue disorders ( i.e. Lupus, Behcet's, Sarcoidosis )
In general, people at higher risk for encephalitis include the very young ,the very old, and those who have compromised immune systems.


What can be done to prevent the condition?

There are a few ways to prevent encephalitis.
  • Diseases such as polio, measles, mumps, chicken pox, and rubella can be prevented by vaccination; therefore, adults and children should stay up to date on physician recommended vaccinations.
  • Practice frequent hand washing when exposed to all animals, raw meat, or eggs.
  • When in the outdoors, adorn long sleeve shirts and pants and use a repellant such as DEET to prevent transmission of diseases by mosquitoes and ticks.
  • If traveling internationally, make sure to get the appropriate vaccinations and prophylactic medications specific to the area where you will be going.
  • Avoid unsafe sexual practices and illicit drug use.


How is the condition diagnosed?

Diagnosis of encephalitis begins with a medical history and physical examination. A spinal tap may be done to obtain a sample of the fluid that bathes the brain and spinal cord.
The doctor may order other tests, including:
  • antibody titer blood tests to detect antibodies to certain organisms
  • blood cultures to detect organisms in the blood
  • cranial CT scan
  • cranial MRI
  • electroencephalogram, also called EEG, which shows brain waves
  • polymerase chain reaction, a blood test that identifies organisms by their genes
  • occasionally a brain biopsy may be warranted to make the diagnosis.

Long Term Effects

What are the long-term effects of the condition?

Brain damage is a possible long-term effect of encephalitis. Some individuals will have permanent disability.

Other Risks

What are the risks to others?

Some of the organisms that cause encephalitis can spread from person to person.


What are the treatments for the condition?

Treatment options vary, depending on what causes the encephalitis. Medicines used to treat encephalitis include the following:
  • acetaminophen or ibuprofen for headache and fever
  • antibiotics for infections caused by bacteria
  • anticonvulsants to treat seizures
  • antiviral medicines for infections caused by a virus
  • corticosteroids to reduce brain swelling
  • sedatives for irritability
People who develop severe and permanent disabilities may be referred to a rehabilitation program once their condition is stable.

Side Effects

What are the side effects of the treatments?

Many of the medicines used to treat encephalitis may cause stomach upset or allergic reactions. Anticonvulsants may cause drowsiness.

After Treatment

What happens after treatment for the condition?

Some people with encephalitis have a mild infection that resolves with effective treatment. Others may have a serious infection leading to permanent disability or death.


How is the condition monitored?

Regular visits to the doctor will be used to monitor recovery from encephalitis. Any new or worsening symptoms should be reported to the doctor.

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