Historical overview of studies on Japanese Encephalitis Virus in northern Vietnam, 1964 – 1978

In northern Vietnam from April to September every year, children often have had a malignant syndrome called Acute Encephalitis Syndrome (AES). From 1965 to 1977, the total number of AES in children was 22,545 cases, from whom 4,774 died. Before 1964, the etiology of AES in northern Vietnam has not yet been identified; so the JE infection in our country is still a blank area on the World Map. In this study, we have to determine the etiology of the AES by carrying-out:
Virus isolation
From 1964 to 1976, we have isolated 22 JEV from different specimens including: 10 from AES children (1 from blood, 9 from brains), 1 from bird, 1 from swine blood, 10 from mosquitoes.
The positive diagnoses (HI test) using paired sera taken from AES children have been varied from 25.58% to 67.5%.
Investigate the JEV circulation through serological survey of healthy humans: During 1964-1978, we have tested 7,868 sera, from which the positive rate varied from 25% to 82.94%.
Vectors transmitting JEV
JEVs were isolated for the first time in 1971 from Culex tritaeniorhynchus. Then in 1975-1976, JEV were discovered from Culex gelidus, Aedes albopictus and Aedes (Sp) diemmaccus. To this time, Culex tritaeniorhynchus has been identified as the main vector transmitting JEV in northern Vietnam.
Explore the circulation of JEV in animals
– Birds: in 1964 we have isolated the strain LD-68 from bird Garrulax perspicillatus – Gmelin and have found 8/14 bird species carrying JE antibody; therefore wild birds have played the role as reservoir of JEV.
– Animals:
a/ Serological survey in swine: In 1970: 606 pig sera have been collected in several localities, from which 63.69% were positive to JEV with MAT: 1/619.76.
b/ Sero-survey in livestock: During 1972-1975, we have continued to investigate sera from other animal species. The results obtained demonstrated that swine was the most commonly infected with JEV to compare with other domestic animals.

Results
With the results obtained, we asserted that northern Vietnam was a natural focus of JEV. This virus virtually persisted everywhere, in wild birds, an arthropod transmitted this virus from bird to livestock; at first to a few pigs, Culex tritaeniorhynchus sucking blood from pigs in phase of viremia then widespreading this virus to other pigs, allowed herd of infected pigs increased rapidly and just to this phase, JE infections occur in humans with a small number of children suffered from AES.

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By Do Quang Ha