One of the most common viral infectious diseases in Asia is Japanese encephalitis. Although outbreaks are usually controlled by mass vaccination and symptoms are usually not severe, in some cases this virus is associated with dangerous inflammation of the brain that can leave significant sequelae or even cause death.

In this article we will describe what Japanese encephalitis is, what causes it and what are its symptoms and main signs. We will also explain where this disease appears frequently and what measures can be taken to prevent it, as well as the care that is usually recommended in case it develops.

What is Japanese encephalitis?

Japanese encephalitis is an infectious disease that is contracted through mosquito bites . It is caused by a virus that is endemic to 24 countries in East, South, and Southeast Asia, as well as the Western Pacific Islands.

In places such as China, Thailand, Korea, Vietnam, India, Indonesia, the Philippines, Taiwan, Myanmar, Sri Lanka, Cambodia, Laos, Nepal and Malaysia, cases of Japanese encephalitis are very common, although there are vaccines to prevent them.

The virus that causes Japanese encephalitis is classified in the flavivirus family , which also includes yellow fever, dengue fever, West Nile virus, and viruses that cause some types of hepatitis.

Although in a large number of cases the virus does not cause the appearance of severe symptoms, more than a third of people suffering from Japanese encephalitis suffer permanent sequelae and approximately 30% die from the alterations caused by brain inflammation.

Signs and symptoms

Most of the time, getting Japanese encephalitis virus does not cause any symptoms, or only headache and fever. However, sometimes an inflammation of the brain (encephalitis) develops that can become severe.

In one out of every 100 or 250 cases the infection progresses to a disease that appears 5 to 15 days after the mosquito bite and can be life-threatening. The characteristic signs and symptoms of this phase are the following :

  • Headache
  • Intense fever
  • Vomiting
  • Disorientation
  • Tremors
  • Seizures
  • Stiffness in the neck
  • Spastic paralysis
  • Brain Coma

Just under a third of people infected with Japanese encephalitis are permanently affected by this virus. It is common for there to be sequelae related to neurological disorders , such as partial paralysis, loss of speech and cognitive and behavioural disorders.

Causes and epidemiology

Japanese encephalitis is mainly transmitted by the mosquito species Culex tritaeniorhynchus and Culex vishnui. Animals such as farm pigs and herons often carry the virus ; mosquitoes infect people and other animals, especially horses, through their bites.

The disease mainly affects populations in rural areas and regions surrounding cities because of the greater proximity of animals; it is also associated with rice cultivation and flood irrigation. In comparison, it is relatively rare in urban areas.

In Asia, approximately 70,000 cases of Japanese encephalitis are reported each year ; the disease causes the death of between 13,000 and 20,000 people annually. However, most people in countries where Japanese encephalitis is endemic become immune after vaccination or after contracting it during childhood.

Large epidemics of Japanese encephalitis tend to occur in summer, although in tropical countries the prevalence is high year-round and increases even more in the rainy season; this is related to the increase in the number of mosquitoes. The frequency of intense outbreaks ranges from approximately 2 to 15 years.

Prevention and treatment

There is no cure for Japanese encephalitis, so the treatment is aimed at reducing the symptoms , as well as favouring the biological processes that allow the elimination of the infection. For these purposes, rest, significant amounts of fluids and antipyretic and analgesic medications are prescribed.

In general, in the countries of Asia and the Pacific where this virus is common, there are medical protocols aimed at minimizing the risk of contracting the disease and suffering its most serious effects, mainly through vaccination and monitoring the appearance of new cases and epidemics .

Since people in other regions of the world are not as prepared to defend themselves against Japanese encephalitis, it is advisable to get preventive vaccination before traveling to places where the virus could be contracted. Also, using repellent products and covering your arms and legs can prevent mosquito bites.