Japanese encephalitis
Version: November 2025
Introduction
Japanese encephalitis is a viral infection caused by the Japanese encephalitis virus (JEV). Transmitted through the bite of infected mosquitoes, particularly Culex species, it predominantly affects rural and peri-urban areas in Asia. The disease is prevalent in regions where rice farming and pig rearing coexist, creating an ideal mosquito habitat. Although most infections are mild or asymptomatic, severe cases result in brain inflammation, leading to symptoms such as high fever, headache, and seizures. These severe cases can be fatal or cause long-term neurological issues. Vaccination is essential for prevention, especially in endemic areas.
Highlights
- Seasonal Trends: Japanese encephalitis cases in mainland China peak during the summer months, particularly from July to September, reflecting a seasonal trend associated with mosquito activity.
- Decline in Cases: The data from 2020 to 2025 show a general decline in the number of cases compared to earlier years, indicating improved control measures or other factors influencing disease dynamics.
- Mortality Reduction: Over the years, mortality has decreased significantly, suggesting advancements in medical treatment and disease management.
- Current Situation: As of November 2025, the number of cases remains relatively low with a slight uptick in recent months, warranting continued surveillance and mosquito control efforts.
Analysis
Cases Analysis
The data on Japanese encephalitis in mainland China from November 2015 to October 2025 highlights a clear seasonal pattern, with cases peaking between July and September. This coincides with warmer temperatures and increased mosquito activity, which are vectors for the virus. Such trends reflect a cyclic nature of the disease outbreak, closely tied to environmental conditions. Notably, years such as 2017 and 2018 experienced significantly high peaks, particularly August 2018 with 904 cases, potentially indicating variances in vector control efforts or favorable conditions for mosquito proliferation.
Mortality trends exhibit fluctuations, often rising during peak months but not always in direct proportion to case numbers. For instance, August 2017 and 2018 saw high cases and deaths, peaking at 55 in August 2018, suggesting differences in healthcare responses or virus virulence. Although yearly totals decreased from 2019, notable peaks in cases and deaths during August to October persist, emphasizing the challenge in controlling this arbovirus and the need for continued public health vigilance. Data from 2021 onwards displays lower case numbers, with occasional spikes, hinting at improved interventions but underscoring that risk remains. Overall, while reductions in cases in recent years show progress, the seasonal nature continues to demand targeted preventive measures during high-risk periods.
Deaths Analysis
An analysis of Japanese encephalitis (JE) deaths in the Chinese mainland from late 2015 to 2025 reveals notable trends and fluctuations. From 2015 to 2018, there were significant spikes in cases, particularly in warmer months like August, corresponding with higher vector activity. Deaths followed a similar pattern, although cooler months such as December 2018 and early 2019 exhibited relatively high fatalities compared to case numbers. These patterns could indicate challenges with healthcare access or the influence of other seasonal health factors.
Starting from 2019, there was a noticeable shift, with both JE cases and deaths generally declining. This trend suggests improved healthcare responses, possibly through better treatment, increased vaccinations, or enhanced public health initiatives. By 2021, both cases and fatalities had significantly decreased, possibly reflecting successful public health strategies to control JE. In 2025, while there was a slight increase in cases during summer months, deaths remained low. This indicates progressing management of severe outcomes and the importance of continued efforts in disease prevention and treatment.
Overall, the data highlights the need for sustaining preventive measures, improving healthcare accessibility, and adapting strategies to address seasonal variations. The reduction in fatalities over the years underscores the effectiveness of targeted public health interventions in mitigating Japanese encephalitis’s impact.