Watching Brief
Date of first report of the outbreak | 1st July 2022 (1) |
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Disease or outbreak | Japanese encephalitis viruse (JEV) infection which is caused by Japanese encephalitis virus, a flavivirus, and is transmitted to humans through the bite of infected culicine mosquitoes (2). |
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Origin (country, city, region) | Assam, Northeast region, India. |
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Suspected Source (specify food source, zoonotic or human origin or other) | Japanese encephalitis is a mosquito borne zoonotic disease. The risk of acquiring infection was found to be high in areas close to paddy fields and water bodies, along with the presence of pig’s habitats. Pigs and wading birds are the amplifying hosts (or the natural reservoirs) of JEV (2). |
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Date of outbreak beginning | 1st July 2022 (1) |
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Date outbreak declared over | Ongoing - the most recent report on Japanese encephalitis in Assam was published on 23rd September 2022 (3). |
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Affected countries & regions |
Figure 1
“Assam, a northeast state in India affected by the Japanese encephalitis outbreak, 2022” (4).
Figure 2
“Districts in Assam, India, affected by Japanese encephalitis outbreak, 2022” (4). Upper Assam: Golaghat, Sivasagar, Dibrugarh, Tinsukia, Lakhimpur, Jorhat, Majuli, Cachar. Southern Assam: Hailakandi Central Assam: Nagaon, Hojai, Morigaon. Lower Assam: Barpeta, Nalbari, Baksa, Chirang and Udalguri. Golaghat in upper Assam is the worst affected district. |
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Number of cases (specify at what date if ongoing) | 434 confirmed cases reported from 1st July to 23rd September 2022 (3). |
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Clinical features | Incubation period: 5-15 days. Symptoms:
Mode of transmission (dominant mode and other documented modes) |
JEV, a flavivirus, is transmitted to humans through the bite of infected Culicine mosquitoes. The Culex vishnui group. C. tritaeniorhynchus, C. vishnui and C. pseudo vishnui are the main vectors of JEV reported in different parts of India. C. tritaeniorhynchus has been reported as the most prominent vector in India (5). It is found in Tamil Nadu, Karnataka and Kerala. C. vishnui subgroups are common, widespread and breed in water with luxuriant vegetation, mainly in paddy fields. The abundance of JEV in these areas is related to rice cultivation, shallow ditches and pools in Tamil Nadu, Karnataka and West Bengal. The other species of Culex mosquitoes are variably isolated from states such as Tamil Nadu, Karnataka, West Bengal, Andhra Pradesh and Goa. There is no evidence of human-to-human transmission till date (6). Demographics of cases |
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Case fatality rate |
Of the 434 JEV cases reported in Assam from July to September 2022, 93 people died (3). The CFR in Assam during this outbreak was 21.43% (3). Underreporting of cases may occur, thus overestimating the case fatality of JEV infection. Complications |
Most people infected with JEV do not develop symptoms or have only mild symptoms. However, a small percentage of infected people develop inflammation of the brain (encephalitis), which is the most serious clinical consequence of a JEV infection. Symptoms include sudden onset of headache, high fever, disorientation, coma, tremors and convulsions. About 1 in 4 cases with encephalitis are fatal (2). Available prevention |
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Available treatment |
There is no specific treatment for JEV. Treatment is symptomatic and includes rest, fluids, and over-the-counter pain medications. Patients who develop severe disease require hospitalization for supportive care and close observation. In Assam, nine medical colleges and ten district hospitals were designated as JEV treatment centres, following standard guidelines of the National Health Mission. Comparison with past outbreaks |
| Unusual features |
| Critical analysis |
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Risk factors for the current JEV outbreak: Key questions |
| Acknowledgements |
This Watching Brief is an output of an epidemiology workshop between The National Institute of Epidemiology and EPIWATCH |
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18. Gaurav Das. Fear of Japanese encephalitis adds to continuing flood woes. The Times of India. (01 August 2016). https://timesofindia.indiatimes.com/city/guwahati/fear-of-japanese-encephalitis-adds-to-continuing-flood-woes/articleshow/53487708.cms (accessed 08 February 2023).
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