What is Japanese Encephalitis?


via The Medical City |  Japanese encephalitis (JE) is a mosquito-borne viral infection, and belongs to the same genus as dengue, yellow fever, and West Nile viruses[1]. It is the leading cause of viral encephalitis in Asia.

In endemic (common disease or condition in a certain area) countries, where adults have acquired immunity through natural infection, JE is primarily a disease of children. However, travel-associated JE can occur among people of any age. For most travelers to Asia, the risk for JE is extremely low but varies based on destination, duration, season, and activities[2].

Japanese Encephalitis in the Philippines

The JE virus was first reported in the country in 1943 and since then, the Philippines has been recognized as a country where the virus normally circulates[3].

The peak season for transmission is not yet well defined, and based on the most recent data from the Department of Health for the year 2017, the number of cases being reported is decreasing compared to the same period in 2016[4].

How is Japanese Encephalitis transmitted?

The JE virus is transmitted to humans through a bite from an infected mosquito, specifically the Culex tritaeniorhynchus. These mosquitoes breed in water pools and flooded rice fields.

It is not the same species as the mosquito that transmits the Dengue, Chikungunya, or Zika virus.

JE is a zoonotic disease, a disease that is transmitted from animals to humans. The JE virus reaches high levels in vertebrate hosts such as pigs and wading birds (considered as amplifying hosts). Once the mosquitoes feed on these hosts, they become capable of infecting humans.

It is important to remember that humans are incidental and dead-end hosts. Humans are incapable of transmitting the virus to mosquitoes as they do not develop and sustain high levels of JE virus in their bloodstream.

There is no human to human transmission.

What are the Signs and Symptoms of Japanese Encephalitis?

Less than one percent of people infected with the JE virus develop clinical illness. Incubation period (time from infection until illness): 5-15 days

Initial Symptoms

  • Fever
  • Headache
  • Vomiting

Other possible symptoms that may develop over the next few days

  • Mental status changes
  • Neurologic symptoms
  • Weakness
  • Movement disorders
  • Seizures – most common especially among children

Among patients who develop Encephalitis, 20-30% die. Although some symptoms improve after the acute illness, 30-50% of survivors continue to have neurologic, cognitive, or psychiatric symptoms[5].

How is Japanese Encephalitis diagnosed?

Individuals who live in or have travelled to a JE endemic area and have experienced encephalitis (a condition wherein the brain becomes inflamed) are considered as a suspected JE case.

Laboratory testing of serum or cerebrospinal fluid (CSF or fluid surrounding the brain and spine) is done to confirm JE virus infection and to rule out causes of encephalitis.

What are the available treatment options?

There is currently no specific treatment for JE. Once diagnosed, management is basically supportive.

What are the available means of disease prevention?

The following are some ways that can help prevent you from acquiring Japanese Encephalitis:

  • Avoidance of mosquito bites
  • Use of personal protective measures such as repellents

The World Health Organization (WHO) recommends having strong JE prevention and control activities, including JE immunization in all regions where the disease is a recognized public health priority, along with strengthening surveillance and reporting mechanisms. Even if the number of JE-confirmed cases is low, vaccination should be considered where there is a suitable environment for JE virus transmission. There is little evidence to support a reduction in the JE disease burden from interventions other than the vaccination of humans.

Currently, the only available Philippine FDA-registered JE vaccine is the live attenuated recombinant (Chimeric) vaccine. 

What are the related services available at The Medical City?

The Medical City has a complete roster of competent doctors who can assess and manage patients with Japanese Encephalitis. You may consult with your doctor regarding Japanese Encephalitis vaccination.

Note: This information is not intended to be used as a substitute for professional medical advice, diagnosis, or treatment. If you or someone you know have any of the symptoms mentioned above, it is advisable to seek professional help.

For inquiries, you may contact:


2/F Emergency Room Mezzanine, Nursing Tower, The Medical City
Tel. No.: (+632) 988-1000 / (+632) 988-7000 Ext. 6323


1)     WHO. Japanese Encephalitis. Fact Sheet No 386. December 2015.
2)     Japanese Encephalitis . Yellow Book. Travellers Health CDChttp//wwwwnc.cdc.gov/travel/yellowbook/2018
3)     World Health Organization. Japanese Encephalitis: surveillance and immunization in Asia  and the Western Pacific, 2016. MMWR June 2017; 23 (92): 321-332.
4)     Position Paper on Japanese Encephalitis Vaccines. Pediatric Infectious Disease Society of the Philippines (A  Specialty Society of the Philippine Pediatric Society)
5)     Japanese Encephalitis. CDC. August 2015. http//www.cdc.gov

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