Japanese Encephalitis

Culex Mosquito. "CulexNil"

India saw an outbreak of Japanese Encephalitis (JE) in the summer of 2014 with multiple deaths. In 2015, the virus has returned. Although there is a vaccine, deaths have been rising from 41 in 2010 to 160 in 2014, with a 5 fold increase in the number of reported case in Assam in the northeast of India. There was also at least 60 deaths in West Bengal.

Changes in climate - with rising temperatures and rainfall changes - may have increased JE transmission. This is in part because warmer temperatures allow for more rice to be grown, with more standing water in rice paddies, which leads to more mosquitoes. The disease also occurs later in the year now, as Culex mosquitoes last longer, not just from May to July, but now until November.

What Is the Disease Like?

Most people infected with JE do not get sick. Only 1% have any symptoms. Those who do develop symptoms usually develop them 5-15 days after the mosquito bite. Initial symptoms include fever, headache, vomiting.

Over the next few days, some will develop more serious disease, about 1 in 250. This can include weakness, even paralysis, other neurologic or movement symptoms. These symptoms resemble Parkinson's with frozen faces, tremors, and stereotyped movements (especially cogwheel rigidity and choreoathetotic movement). There may be paralysis - which is acute and flaccid and hence resembles polio. Seizures may occur.

What Happens?

Among those who develop encephalitis, 20-30% die. Of those who survive, 30-50% continue to have mental/neurologic or psychiatric symptoms.

How Does It Spread?

The virus spreads by mosquito bites, especially from Culex tritaeniorhynchus and Culex vishnui (especially in India as well as Sri Lanka and Thailand). This disease is most prevalent in Southeast Asia and East Asia. The disease occurs in 24 countries in Asia and the Western Pacific region where 3 billion people live. The disease is not found in many urban areas, especially in countries like Japan where it has been under control, as well as Korea where there has been mass vaccination.

In many areas, transmission is seasonal - summer and fall.

The virus is maintained between mosquitoes and pigs, as well as some birds. Humans are "dead end hosts" meaning they cannot transmit infection (as the virus levels remain too low in our blood for mosquitoes to transmit to anyone else). Horses and sometimes cattle also develop dead end infections which can be deadly, but which also do not transmit the infection. There is concern that by having pig farming close to humans that we risk spreading JE to humans.

How Is It Diagnosed?

Diagnosis is made through a clinical exam and history and then confirmed through laboratory testing. Blood or cerebrospinal fluid can be tested for early antibodies (IgM) which appear 3-8 days after the illness started and continue up to 1-3 months or more after the disease onset).

The cerebrospinal fluid will also show a moderate elevation in white blood cells (with lymphocytes), normal glucose, and slightly elevated protein. Blood will show moderate elevation in white blood cells, drop in red blood cells and sodium. An MRI may show changes in the thalamus as well as possibly the basal ganglia, midbrain, pons, and medulla. 

Is There a Vaccine?

There is a vaccine. The US vaccine is a 2 dose vaccine dosed 28 days apart with the final dose 1 week or more before travel. It is recommended only for those who will be traveling outside of urban areas for at least 1 month during the JE transmission season. It is licensed for those 2 months of age and older. A booster dose can be given 1 year later if there is continued exposure for those over age 17, but it is unclear whether boosters are needed.

There are other vaccines that are also used in endemic areas.

Is There a Treatment?

There isn't specific treatment. Hospitalization for supportive care (fluids, pain meds) is often required.

How to Avoid Infection:

  • Avoid areas with known transmission
  • Use insect repellant that includes DEET
  • Wear long sleeves and pants
  • Be vaccinated if appropriate
  • Avoid going outside at times when there are the most mosquitoes
  • Sleep under a bed net, use air conditioning if possible and close windows and screens
Was this page helpful?