Japanese Encephalitis

### Japanese Encephalitis: Epidemiological Details

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Japanese Encephalitis (JE) is a viral infection caused by the Japanese encephalitis virus (JEV), which belongs to the Flavivirus genus. It is a significant public health concern in Asia and parts of the western Pacific. Here are the detailed epidemiological aspects of JE:

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#### Geographic Distribution

- Endemic Regions: JE is primarily found in Southeast Asia, the Indian subcontinent, parts of China, and the western Pacific islands.

- Non-Endemic Areas: Sporadic cases can occur in non-endemic regions, primarily through travel-related exposure.

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#### Transmission

- Vectors: The virus is transmitted by Culex mosquitoes, particularly Culex tritaeniorhynchus.

- Reservoir Hosts: Pigs and wading birds act as major reservoirs for the virus.

- Human Infection: Humans are incidental hosts and do not contribute significantly to the virus transmission cycle.

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#### Incidence

- Annual Cases: Approximately 68,000 clinical cases of JE occur annually, but the incidence varies significantly between regions.

- Seasonality: JE incidence peaks during the rainy season, coinciding with increased mosquito activity.

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#### Risk Factors

- Rural Agricultural Areas: Higher risk in rural areas where rice farming is prevalent, as these environments provide ideal breeding grounds for mosquitoes.

- Exposure to Vectors: Increased exposure to mosquitoes, particularly during the evening and nighttime.

- Lack of Vaccination: Higher risk in unvaccinated populations, especially children and travellers to endemic regions.

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#### Clinical Features

- Asymptomatic Infections: Most JEV infections are asymptomatic or result in mild symptoms.

- Severe Disease: Approximately 1 in 250 infections leads to severe clinical illness characterized by high fever, headache, neck stiffness, disorientation, seizures, and coma.

- Case Fatality Rate: The case fatality rate for severe JE ranges from 20% to 30%.

- Neurological Sequelae: 30% to 50% of survivors may experience long-term neurological sequelae, including cognitive impairment, motor deficits, and psychiatric issues.

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#### Diagnosis

- Laboratory Tests: Diagnosis is primarily based on the detection of JEV-specific IgM antibodies in cerebrospinal fluid (CSF) or serum using enzyme-linked immunosorbent assay (ELISA).

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#### Prevention

- Vaccination:

? - Inactivated Vero cell-derived vaccine (JE-VC): Recommended for travellers to endemic areas and residents of endemic regions.

? - Live attenuated vaccine (SA 14-14-2): Widely used in endemic regions, particularly in Asia.

- Mosquito Control: Use of insect repellents, bed nets, and other vector control measures to reduce mosquito bites.

- Personal Protective Measures: Wearing long-sleeved clothing and avoiding outdoor activities during peak mosquito activity times.

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#### Public Health Impact

- Vaccination Programs: Mass immunization campaigns in endemic regions have significantly reduced the incidence of JE.

- Surveillance and Control: Enhanced surveillance and vector control programs are critical in managing and preventing JE outbreaks.

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#### References

- [World Health Organization (WHO) - Japanese Encephalitis](https://www.who.int/news-room/fact-sheets/detail/japanese-encephalitis)

- [Centers for Disease Control and Prevention (CDC) - Japanese Encephalitis](https://www.cdc.gov/japaneseencephalitis/index.html)

- [PubMed - Epidemiology of Japanese Encephalitis](https://pubmed.ncbi.nlm.nih.gov/)

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By understanding these epidemiological details, public health authorities can implement effective strategies for the prevention, control, and management of Japanese encephalitis.