Japanese Encephalitis: Symptoms, Diagnosis, and Treatment

Symptoms

In persons who develop symptoms of Japanese encephalitis, the time from infection until illness onset (incubation period) is typically 5–15 days.

• Initial symptoms often include fever, headache, and vomiting.
• Disorientation, weakness, and coma might develop over the next few days.
• Seizures are common, especially among children.

No symptoms in most people. Most people (more than 99%) infected with Japanese encephalitis virus do not have symptoms or have only mild symptoms.

People who develop neurologic illness. Less than 1% of people infected with Japanese encephalitis virus develop neurologic illness. Among patients who develop encephalitis (inflammation of the brain), about 1 in 4 (20–30%) die.

Lasting symptoms for those who developed neurologic illness. Although some symptoms improve after the acute illness, 30%-50% of patients who develop encephalitis and survive continue to have movement, thinking, or behavioral symptoms.

Diagnosis

See your healthcare provider if you have traveled to an area where Japanese encephalitis is present and develop the symptoms described above.

• Tell your healthcare provider when and where you traveled.
• Your healthcare provider can order tests to look for Japanese encephalitis virus infection.

To learn more about testing, visit our Healthcare Providers page.

Treatment

• There are no medicines available to treat Japanese encephalitis. Treatment is focused on relieving symptoms. However, a vaccine is available to prevent disease.
• Rest, fluids, and over-the-counter pain medications may relieve some symptoms.
• Hospitalization for supportive care and close observation is generally required.

To learn more about treatment, visit our Healthcare Providers page.