Types of Encephalitis

What is encephalitis?

Encephalitis is an inflammation of the brain that is often caused by a viral infection. The arboviruses cause encephalitis and are passed on to people and animals by insects.

There have been outbreaks in recent years in the U.S. of several types of encephalitis, such as West Nile encephalitis and St. Louis encephalitis. Travelers abroad are most at risk for Japanese encephalitis and tick-borne encephalitis.

Japanese encephalitis is mosquito-borne and occurs mainly in:

  • China, Japan, and Korea
  • Eastern Russia

Japanese encephalitis also occurs less often in Republic of China (Taiwan), Singapore, and Hong Kong. In all of these areas, Japanese encephalitis is mainly a rural disease.

On average, among people who are infected by a mosquito bite, very few will develop an illness. Most people who are infected develop only mild or no symptoms. But among people who develop encephalitis, the results are serious.

Tick-borne encephalitis is a viral infection of the central nervous system passed on by bites of certain ticks. The disease occurs in:

  • Scandinavia
  • Western and Central Europe
  • The countries that made up the former Soviet Union

People can be infected by the bite of infected Ixodes ricinus ticks. This usually happens in people who visit or work in forests, fields, or pastures. You can also get the infection by consuming unpasteurized dairy products from infected cows, goats, or sheep.

The risk of getting the disease is greatest from April through August. This is when ticks are most active.

What causes arbovirus encephalitis?

The arboviruses that cause encephalitis are passed on to people and animals by insects. In rural areas, arboviruses that are carried by mosquitoes or ticks are the most common cause of arboviral infection. The infection is often mild, but it can progress to encephalitis.

What are the symptoms of arbovirus encephalitis?

The following are the most common symptoms of encephalitis caused by arboviruses:

  • Headache
  • Feeling unwell
  • Drowsiness
  • Fever
  • Vomiting
  • Stiff neck
  • Muscle soreness or trembling
  • Confusion
  • Convulsions
  • Sensitivity to light
  • Extreme weakness

The symptoms of arbovirus encephalitis may look like other health conditions or problems. Always see your doctor for a diagnosis.

How is arbovirus encephalitis diagnosed?

Most infections do not cause symptoms. When they do cause symptoms they may be similar to the flu. Symptoms may start gradually. Or they may be sudden. But the infection may progress to inflammation of the brain (encephalitis). Encephalitis may result in death or cause permanent nervous system problems. Fortunately, only a small portion of infected people develop encephalitis.

Healthcare providers will use blood tests and tests of cerebrospinal fluid to find the virus. 

How is arbovirus encephalitis treated?

Because this is a viral disease, antibiotics will not help. There are no effective antiviral medicines at this time. There is no specific treatment for encephalitis. The main goal is to ease symptoms and keep the person's breathing and circulation working well while the infection runs its course.
Your healthcare provider will determine the best treatment for you based on:

  • How old you are
  • Your overall health and past health
  • How sick you are
  • How well you can handle specific medicines, procedures, or therapies
  • How long your condition is expected to last
  • Your opinion or preference

Can arbovirus encephalitis be prevented?

A vaccine for Japanese encephalitis is currently available in the U.S. through most travelers' clinics. The CDC generally recommends the vaccine only for people who will travel in rural areas for 4 weeks or more. It is also recommended where there is a known outbreak of Japanese encephalitis.

As a traveler, take steps to prevent insect bites, including the following:

  • Limit how much time you spend outdoors during the cooler hours at dusk and dawn. This is when mosquitoes that pass on the disease feed.
  • Wear mosquito repellents containing DEET as an active ingredient.
  • Stay in air-conditioned or well-screened rooms.

If you are traveling to rural areas, bring a portable bed net. Use permethrin, a mosquito repellent/insecticide, on both the bed net and clothing.

Another way to prevent encephalitis is with mosquito control. In many emergency cases, the best method is with aerial spraying. Many states may use aerial spraying to control mosquitoes. They can also spray in areas where the virus is active.

To protect yourself against tick-borne encephalitis, follow these recommendations:

  • Stay away from tick-infested areas.
  • Wear clothing that will help you avoid being bitten.
  • Use repellents containing DEET. These can be put directly on skin.
  • Use permethrin on clothing and camping gear.
  • Don't drink or eat unpasteurized dairy products.


When should I call my healthcare provider?

Call your healthcare provider if you have the following symptoms:

  • Headache
  • Drowsiness
  • Fever of 100.4°F (38°C) or higher, or as advised by your healthcare provider 
  • Vomiting
  • Stiff neck
  • Muscle trembling
  • Confusion
  • Convulsions
  • Light sensitivity

Key points on arbovirus encephalitis

  • Encephalitis is an inflammation of the brain that is often caused by a viral infection. Arboviruses can cause  encephalitis.
  • Arboviruses are passed on to people and animals by insects. In rural areas, mosquitoes and ticks are the most common carriers.
  • The viral infection is usually mild. But it can progress to encephalitis.
  • There is no treatment for encephalitis. Treatment is usually to relieve symptoms while the virus runs its course.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

  • Know the reason for your visit and what you want to happen.
  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
  • Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
  • Ask if your condition can be treated in other ways.
  • Know why a test or procedure is recommended and what the results could mean.
  • Know what to expect if you do not take the medicine or have the test or procedure.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.


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