Japanese Encephalitis
Compiled By : Assoc.Prof. Chukiat Sirivichayakul
Assist.Prof. Achara Asavanich
Assist.Prof. Achara Asavanich
Produced By : Information leaflet committee, Faculty of Tropical Medicine,
Mahidol University and Department of Disease Control, Ministry
of Public Health
Mahidol University and Department of Disease Control, Ministry
of Public Health
Japanese encephalitis (JE) virus. Transmission to man is mainly by the mosquito Culex tritaeniorrhynchus, which breeds in rice fields.
Transmission
Pigs are amplifying hosts of this virus. The JE virus multiplies rapidly, resulting in viremia, but the pig remains asymptomatic. When the mosquito vector feeds on an infected pig, the virus multiplies in the mosquito and is transmitted to man or other animals, such as horse, cattle, sheep and bird, through mosquito bite.
Pigs are amplifying hosts of this virus. The JE virus multiplies rapidly, resulting in viremia, but the pig remains asymptomatic. When the mosquito vector feeds on an infected pig, the virus multiplies in the mosquito and is transmitted to man or other animals, such as horse, cattle, sheep and bird, through mosquito bite.
Endemic areas
This disease was first recognized in Japan. Currently, it is found widely in East Asia, Southeast Asia and South Asia. In Thailand, high incidence is found where rice and pig farms coexist, especially in Mae Hong Son, Mukdahan, Kamphaeng Phet, Samut Sakhon and Nan provinces.
This disease was first recognized in Japan. Currently, it is found widely in East Asia, Southeast Asia and South Asia. In Thailand, high incidence is found where rice and pig farms coexist, especially in Mae Hong Son, Mukdahan, Kamphaeng Phet, Samut Sakhon and Nan provinces.
Symptoms
Approximately 1 in 300 JE virus infected persons become ill. The incubation period is 5-15 days. The illness starts with high fever, vomitting, headache and weakness. One to seven days later (usually 2-3 days), neurological signs and symptoms, such as stiff neck, drowsiness, delirium, convulsions, unconsciousness, tremor and paralysis may occur for 3-6 days. Those with severe conditions may die at this stage (the mortality rate is 15-30%).
Finally, the fever gradually subsides, followed by improved neurological conditions. However, about half of the survivors have severe sequelae, such as spasms, paralysis, convulsions, mental retardation, speech disorders and emotional disturbances.
Approximately 1 in 300 JE virus infected persons become ill. The incubation period is 5-15 days. The illness starts with high fever, vomitting, headache and weakness. One to seven days later (usually 2-3 days), neurological signs and symptoms, such as stiff neck, drowsiness, delirium, convulsions, unconsciousness, tremor and paralysis may occur for 3-6 days. Those with severe conditions may die at this stage (the mortality rate is 15-30%).
Finally, the fever gradually subsides, followed by improved neurological conditions. However, about half of the survivors have severe sequelae, such as spasms, paralysis, convulsions, mental retardation, speech disorders and emotional disturbances.
Diagnosis
The disease can be diagnosed by physical examination along with the history of living in or entering endemic areas. Detection of antigens and antibodies to JE virus from serum and spinal fluid are considered the most accurate.
The disease can be diagnosed by physical examination along with the history of living in or entering endemic areas. Detection of antigens and antibodies to JE virus from serum and spinal fluid are considered the most accurate.
Treatment
There is no specific anti-JE drug currently available. Only symptomatic and supportive treatments are provided to prevent the complications that may occur.
There is no specific anti-JE drug currently available. Only symptomatic and supportive treatments are provided to prevent the complications that may occur.
Prevention
After vaccination was applied in Japan, China and Korea, the number of patients in these countries was reduced dramatically. JE virus vaccine is available in Thailand. Self-protection and reduction of man-mosquito contact by application of repellent or the use of a bed-net are advisable. Control of mosquito vectors in rice fields and pig-farming areas may require a major effort, since Thailand is considered an agricultural country.
A person who has never received vaccination and plans to enter an endemic area should be completely vaccinated at least two weeks before arrival.
After vaccination was applied in Japan, China and Korea, the number of patients in these countries was reduced dramatically. JE virus vaccine is available in Thailand. Self-protection and reduction of man-mosquito contact by application of repellent or the use of a bed-net are advisable. Control of mosquito vectors in rice fields and pig-farming areas may require a major effort, since Thailand is considered an agricultural country.
A person who has never received vaccination and plans to enter an endemic area should be completely vaccinated at least two weeks before arrival.
