Conditions & Treatments


Encephalitis is an inflammation caused by a viral infection.

Types of Arbovirus Encephalitis

What is encephalitis?

Encephalitis is an inflammation of the brain that is frequently caused by a viral infection. The viruses are called arboviruses and are transmitted 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, which is often mild, but can progress to encephalitis.

While there have been outbreaks in recent years in the United States of several forms of encephalitis, such as West Nile encephalitis and St. Louis encephalitis, travelers abroad are most at risk for Japanese encephalitis and tickborne encephalitis.

What is Japanese encephalitis?

Japanese encephalitis is a mosquito-borne viral disease that occurs mainly in:

  • China, Japan, and Korea

  • Eastern Russia

Japanese encephalitis also occurs at a lower frequency in Taiwan, Singapore, and Hong Kong. In all of these areas, Japanese encephalitis is primarily a rural disease.

Occurrence of the disease is quite low. On average, among persons who are infected by a mosquito bite, only a very few will develop an illness. While the majority of persons who are infected develop only mild or no symptoms, among those who develop encephalitis, the consequences are grave.

How can Japanese encephalitis be prevented?

A vaccine for Japanese encephalitis is currently available in the United States through most travelers' clinics. The Centers for Disease Control and Prevention generally recommends the vaccine only for persons who will travel in rural areas for four weeks or more, except for circumstances where there is a known outbreak of Japanese encephalitis.

In addition, travelers should take precautions to prevent insect bites, including the following:

  • Minimize outdoor exposure during the cooler hours at dusk and dawn, when mosquitoes that transmit the disease feed.

  • Wear mosquito repellents containing DEET as an active ingredient.

  • Stay in air-conditioned or well-screened rooms.

In addition, travelers to rural areas should bring a portable bednet and apply permethrin, a mosquito repellent/insecticide to both the bednet and clothing.

What is tickborne encephalitis?

Tickborne encephalitis is a viral infection of the central nervous system transmitted by bites of certain vector ticks. The disease occurs in:

  • Scandinavia

  • Western and Central Europe

  • The countries that made up the former Soviet Union

Human infections follow bites of infected Ixodes ricinus ticks, usually in persons who visit or work in forests, fields, or pastures. The infection may also be acquired by consuming unpasteurized dairy products from infected cows, goats, or sheep.

The risk of acquiring the disease is greatest from April through August, when the tick vector is most active.

How can tickborne encephalitis be prevented?

Although vaccines are available in Europe, current data does not support travelers receiving the vaccine. Instead, it is advised that travelers protect themselves by adhering to the following recommendations:

  • Avoid tick-infested areas.

  • Dress appropriately to avoid being bitten.

  • Use repellents containing DEET, which can be applied directly on skin.

  • Use permethrin on clothing and camping gear.

  • Avoid unpasteurized dairy products.

What are the symptoms of arbovirus encephalitis?

The following are the most common symptoms of encephalitis caused by arboviruses. However, each individual may experience symptoms differently. Symptoms may include:

  • Headache

  • Drowsiness

  • Fever

  • Vomiting

  • Stiff neck

  • Muscle trembling

  • Confusion

  • Convulsions

  • Photophobia (light sensitivity)

The symptoms of arbovirus encephalitis may resemble other medical conditions or problems. Always consult your doctor for a diagnosis.

What is the treatment for arbovirus encephalitis?

There is no specific treatment for encephalitis and treatment is generally supportive with maintenance of respiratory and circulatory support while the infection runs its course. Specific treatment for encephalitis will be determined by your doctor based on:

  • Your age, overall health, and medical history

  • Extent of the disease

  • Your tolerance for specific medications, procedures, or therapies

  • Expectations for the course of the disease

  • Your opinion or preference

Treatment Programs

Massachusetts General Hospital understands that a variety of factors influence patients' health care decisions. That's just one reason why we're dedicated to ensuring patients understand their diagnosis and treatment options. Because a single option might not serve all patients, we offer a wide range of coordinated treatments and related services across the hospital. Patients should consult with their primary care doctor or other qualified health care provider for medical advice and diagnosis information.

Select a treatment program for more information:


  • Adult Medicine Imaging
    The Adult Medicine Imaging Program at Massachusetts General Hospital Imaging offers a wide range of diagnostic exams and minimally invasive, image-guided treatments, all provided using leading-edge equipment and interpreted by specialty-trained radiologists.
Department of Neurology

  • Neurology-Infectious Diseases Program
    In the Neurology-Infectious Diseases Program, we work with other infectious disease specialists to diagnose and treat infections of the nervous system, and neurological complications of systemic infections.
Speech, Language and Swallowing Disorders

  • Cognitive Rehabilitation Therapy
    This therapy approach is designed to help the individual develop skills and learn compensatory strategies to improve how he/she functions at home, school, and/or at work. This type of therapy addresses difficulties with attention, learning new information, memory, time management, planning, organization, and problem-solving. Tailored to meet the individual needs of the patient with cognitive and executive function deficits, our approach emphasizes the development of metacognitive and self-awareness skills.

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