Japanese Encephalitis

Japanese Encephalitis


Japanese encephalitis virus (JEP)is a mosquito-borne viral infection. It is a flavivirus related to dengue, yellow fever and West Nile viruses and is the leading cause of viral encephalitis in Asia. JEP is most common in Southern Asia

Humans can get the disease when a mosquito that carries the virus bites them. JEP cannot be spread from person to person. Less than 1% of those infected show any symptoms. link . However, the World Health Organisation say that JEP is fatal to 30% of people who do contract it. JEP is an  inflammation of the brain that can cause headache, fever, confusion, seizures, and death. The virus can infect horses and pigs, as well as humans. This can lead to JEP in horses and miscarriage in pigs. When mosquitoes infect an animal, the animal might become a carrier of the virus. When other mosquitos feed on these animals that have newly acquired the virus, they take it on board and infect other animals.


There is no cure for the disease. Treatment is focused on relieving severe clinical signs and supporting the patient to overcome the infection. Most JEP infections are mild fevers and headaches or without apparent symptoms, but approximately 1 in 250 infections results in severe clinical illness. The incubation period is between 4-14 days.

In children, gastrointestinal pain and vomiting may be the dominant initial symptoms.

Severe disease is characterised by rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and ultimately death. The case-fatality rate can be as high as 30% among those with disease symptoms.

Of those who survive, 20%–30% suffer permanent intellectual, behavioural or neurological sequelae such as paralysis, recurrent seizures or the inability to speak. link


A laboratory test is required to confirm JEP.


There is no antiviral treatment for patients with JEP. Treatment is supportive to relieve symptoms and stabilise the patient.


Safe and effective vaccines are available to prevent disease. WHO recommends having strong JEP prevention and control activities, including JEP immunization in all regions where the disease is a recognised public health priority, 

To reduce the risk for JEP, all travellers to Japanese encephalitis-endemic areas should take precautions to avoid mosquito bites.

Personal preventive measures include the use of mosquito repellents, long-sleeved clothes, coils and vaporisers. Travellers spending extensive time in JEP endemic areas are recommended to get vaccinated before travel.