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Flavivirus infections in Chiang Mai area, Thailand, in 1982
Abstract:
Infection by JE virus still constitutes major cause of encephalitis in Chiang Mai Area, although some cases of possible dengue encephalopathy were observed. In spite of many apparent encephalitis cases, infection of vector mosquitoes by JE virus was not demonstrated. Virus isolation from hospitalized patients showed that the principal type of dengue virus circulating in Chiang Mai in 1982 was type 1 virus. Seroepidemiological survey on healthy humans indicated that the northern part of Chiang Mai Province in the region of the Maekong Valley has not yet been invaded so much by dengue viruses, compared with the Chiang Mai Valley, where dengue infection apparently became more prevalent than 12 years ago. The survey also indicated that the spread of JE virus in the study area was not uniform. Survey on vertebrates showed that anti-JE antibodies were highly prevalent among swine, horses, mules, sheep, and dogs. On the other hand, antibody prevalence was low in monkeys, ducks, and sparrows, and was negative among chickens and lizards. IgM-ELISA appeared to help differential diagnosis on JE from dengue even when the HI test did not give positive results.
Insights
Japanese encephalitis (JE) virus remains a primary cause of encephalitis in Chiang Mai. Dengue virus type 1 was prevalent in 1982, with varying JE virus spread and high JE antibodies in domestic animals.
Area of Science:
- Medical Entomology
- Virology
- Epidemiology
Background:
- Japanese encephalitis (JE) virus is a significant cause of encephalitis in Chiang Mai.
- Dengue encephalopathy cases were observed, but JE virus infection in local mosquitoes was not confirmed.
- The prevalence of dengue virus has increased in the Chiang Mai Valley over 12 years.
Purpose of the Study:
- To investigate the epidemiology of JE virus and dengue virus in Chiang Mai.
- To identify the circulating dengue virus serotype and assess JE virus spread.
- To determine the prevalence of JE virus antibodies in vertebrate hosts.
Main Methods:
- Virus isolation from hospitalized patients.
- Seroepidemiological surveys in humans and vertebrates.
- Immunoglobulin M-Enzyme-Linked Immunosorbent Assay (IgM-ELISA) and Hemagglutination Inhibition (HI) tests.
Main Results:
- Dengue virus type 1 was the predominant serotype isolated in 1982.
- JE virus spread was non-uniform across the study area.
- High prevalence of anti-JE antibodies was found in swine, horses, mules, sheep, and dogs.
- Low or negative antibody prevalence was observed in monkeys, ducks, sparrows, chickens, and lizards.
- IgM-ELISA showed potential for differentiating JE from dengue, especially when HI tests were inconclusive.
Conclusions:
- JE virus remains a major etiological agent of encephalitis in Chiang Mai.
- Dengue virus type 1 is actively circulating, with increased prevalence in the Chiang Mai Valley.
- Domestic animals, particularly swine and equines, are significant reservoirs for JE virus.
- IgM-ELISA is a valuable tool for differential diagnosis of JE and dengue encephalitis.