Japanese encephalitis:  Another mosquito-borne disease to watch out for


Any sickness is hard to detect among infants and young children. That is why parents or guardians are generally asked to look out for vomiting, a bulging fontanel (soft area on the top center of the head), and incessant crying that does not get better when the baby is picked up and comforted and body stiffness.

While these signs may be manifestations of common, treatable diseases, parents should not be complacent. If the child exhibits the above-mentioned symptoms, there is a possibility that he or she is afflicted with encephalitis.

Encephalitis is defined as inflammation (swelling up) of the brain resulting from a viral, bacterial or parasitic infections or when the body’s own immune system mistakenly attacks brain tissue. But the most common cause is a viral infection. The brain swells (becomes inflamed) as a result of the body’s attempt to fight off the infections.

Encephalitis generally begins with fever and headache. The symptoms rapidly worsen, and there may be seizures (fits), confusion, drowsiness and loss of consciousness, and even coma.

According to a medical web site, www.medicalnewstoday.com, encephalitis can be life-threatening, but this is very rare. However, in severe cases the person may experience very severe headaches, nausea, vomiting, confusion, disorientation, memory loss, speech problems, hearing problems, hallucinations, as well as seizures and possibly coma. In some cases the patient can become aggressive.

Immunization is the most effective way of reducing the risk of developing encephalitis. This include vaccines for measles, mumps, rubella, and if the virus exists in those areas, Japanese encephalitis and tick-borne encephalitis.

In areas known to have mosquitoes that carry encephalitis-causing viruses, take measures to reduce the risk of being bitten. This may include wearing appropriate clothing, avoiding mosquito-infested areas, avoiding going outside at specific times during the day when there are lots of mosquitoes about, keeping your home mosquito-free, using mosquito repellant, and making sure there is no stagnant water about your house.


What is Japanese encephalitis?

Japanese encephalitis (JE) is an infection of the brain caused by the Japanese encephalitis virus. The virus belongs to the same family as Dengue and, just like Dengue, is primarily transmitted by a mosquito vector. The mosquito vector (Culex tritaeniorhynchus) is different from the mosquito vector of Dengue. Although it tends to be more common in rural, rice-growing regions and in areas where livestock, e.g. pigs, are raised, it has also been reported in urban areas.

“That’s because people travel, communities are expanding out to previously rural areas and mosquitoes can travel as well, among many other factors. JE is found only in Asia, where it is the most common vaccine-preventable form of encephalitis. So, while the name is Japanese encephalitis, it is not limited to Japan and is found practically in the entire Asian region,” Dr. Jaime Santos, told the BusinessMirror.

Santos is past president of the Pediatric Infectious Disease Society of the Philippines. In an e-mail interview, he said the signs and symptoms of JE are like any other form of encephalitis (there are many causes of viral encephalitis) varying from mild to severe. Fever, headache, vomiting and other nonspecific symptoms are common in symptomatic patients, together with convulsions, changes in sensorium including coma and neurologic deficits. Neurologic deficits, e.g., paralysis, convulsions and learning difficulties can persist as sequelae even if the patient has recovered from the acute episode of infection.

“Thus, patients who have JE can eventually become a significant burden to families, the health-care system and the society as a whole,” Santos said.

According to the World Health Organization (WHO), 24 countries in the Southeast Asia and Western Pacific regions have endemic JE transmission, exposing more than 3 billion people to risks of infection. Unfortunately, the Philippines is included among these countries, Santos said.

He said it is only lately that more information has come to light following a few studies on epidemiology of JE. For the latest collated data, he cited the latest reference: Lopez AL. et.al. Epidemiology of Japanese Encephalitis in the Philippines: A Systematic Review. PLOS Neglected Tropical Diseases. DOI:10.1371/journal.pntd.0003630. March 20, 2015, this is freely accessible in the internet.

“Because it is often underreported and unrecognized for various reasons, there is a lack of confirmatory lab facilities in many areas and lack of disease surveillance in the past, the public is often not aware of it,” Santos reported. He also cited the conclusions of the study, as follows:


  •   JE constitutes a significant public-health burden in all regions of the Philippines
  •   Supports the inclusion of JE vaccine in the national immunization program
  •   The lack of reported acute encephalitis cases, as well as JE cases, in some provinces suggests a weakness in disease surveillance rather than the absence of disease


Santos also noted that, in endemic areas for JE, the burden of disease is greatest in the young. In the absence of immune protection in the form of antibodies to the virus, the young are the most susceptible. Infections, therefore, occur mostly in the pediatric population.

“A lot of infected individuals do not develop disease but develop antibodies, which subsequently protects them from getting the disease as adults. So in endemic areas, a lot of adults already have natural immunity, unless they never got infected earlier in life,” he explained.


Vaccination against Japanese encephalitis

For diseases transmitted by vectors like mosquitoes, according to Santos, control can only be achieved using multiple strategies which are time-consuming, costly and difficult to accomplish.

“That is why vaccination is the recognized key to control of JE. Countries that have implemented JE vaccination have managed to reduce the burden of disease. This is true of Japan and Thailand, for example. A lot of countries now, including our neighboring countries, have implemented JE vaccination
either as targeting entire populations or select areas, where burden of disease is highest,” Santos said.