Definition

Japanese encephalitis is an infection from a mosquito. Rarely, it can affect the brain and nervous system. When this happens, it can be serious and even life-threatening.

Causes

Japanese encephalitis is caused by a virus. It is spread to humans from the bite of an infected mosquito. The virus is not spread from person to person.

Risk Factors

The risk of Japanese encephalitis is highest in areas that have outbreaks. Outbreaks have happened in rural parts of China, Korea, Japan, Taiwan, and Thailand. These countries now control the disease with vaccinations.

Countries that still have outbreaks are:

• Vietnam, Cambodia, and Myanmar
• Malaysia, India, and Nepal.

Lab workers exposed to the virus also have some risk.

Symptoms

Most people infected with Japanese encephalitis do not have symptoms. If symptoms happen, they can range from mild to severe.

Symptoms may be:

• Fever and chills
• Headache or neck stiffness
• Nausea or vomiting
• Confusion
• Uncontrolled body movements
• Not being able to move
• Lack of responsiveness or coma

Diagnosis

The doctor will ask about your symptoms and health history. A physical exam will be done.

Tests may be done to diagnose the infection. They may be:

• Blood tests
• Lumbar puncture—to check brain and spinal cord fluid

Imaging tests may be done to check the brain. They may include:

• CT scan
• MRI scan

Treatment

There is no specific treatment for Japanese encephalitis. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. Hospital care may be needed.

Depending on the symptoms, options may be:

• Pain medicines—for headaches
• Anti-nausea medicines
• Fluids—by mouth or IV
• Breathing support

Prevention

The risk of Japanese encephalitis may be reduced by:

• A vaccine, which may be given to those who:
  • Live or travel to certain parts of Asia
  • Are lab workers at risk for exposure to the virus

The risk may also be reduced by:

• Avoiding mosquito bites by:
  • Covering up the skin
  • Using bug sprays, netting, and screens
  • Staying inside between dusk and dark