[Surveillance for Japanese encephalitis in Henan Province, 2004-2025]

Objective: To analyze the epidemiological characteristics of Japanese encephalitis (JE) in Henan Province from 2004 to 2025, and the results of antibody among the healthy population and mosquito surveillance at sentinel sites in 2012. Methods: A descriptive epidemiological analysis was conducted of JE case data in Henan Province from 2004 to 2025 obtained from the China Information System for Disease Control and Prevention. In 2012, Luoyang and Xinyang Cities were selected as surveillance sites. Blood samples were collected from healthy individuals across eight age groups, and neutralizing antibodies against the JE virus were detected using a micro-plaque reduction neutralization test. Mosquito specimens were collected using the person-hour method to calculate mosquito density and isolate the JE virus. Results: From 2004 to 2025, the incidence rate of JE in Henan Province decreased from 0.94/100 000 to 0.01/100 000, showing an overall downward trend average annual percentage change (AAPC)=-13.00% (95%CI:-30.00% - -10.00%, P=0.004). The cases mainly occurred from July to September (91.21%, 4 211/4 617). The distribution of cases was predominantly in the southern regions of Henan Province (Nanyang, Xinyang, Luoyang, Zhumadian, Zhoukou, and Shangqiu), accounting for 76.69% (3 541/4 617). Cases aged 0-14 years accounted for 78.32% (3 616/4 617), but the incidence in the population aged ≥15 years showed an increasing trend (AAPC=8.87%, 95%CI: 4.76%-13.71%, P<0.001), with a particularly significant increase in those aged ≥40 years (AAPC=11.93%, 95%CI: 7.32%-16.99%, P<0.001). In Luoyang City, cases aged ≥15 years accounted for 63.62% (376/591), significantly higher than the provincial average (21.68%, 1 001/4 617). The difference in the proportion of cases aged ≥15 years between Henan Province and Luoyang City was statistically significant (χ²=471.69, P<0.001). At surveillance sites in Luoyang City and Xinyang City in 2012, the positive rate of JE antibodies among the healthy population aged ≥15 years in Luoyang City was 53.28% (65/122), significantly lower than that in Xinyang City (91.34%, 116/127), which was consistent with the predominance of cases in the population aged ≥15 years in Luoyang City and cases aged 0-14 years in Xinyang City. The peak mosquito density in Luoyang City occurred in August, which was one month later than in Xinyang City, consistent with the peak JE incidence in Luoyang City occurring in September, one month later than that in Xinyang City. Five strains of genotype ⅠJE virus were isolated from mosquitoes in the two cities. Conclusions: From 2004 to 2025, the incidence of JE in Henan Province declined while the incidence in the ≥15 age group increased. The age distribution and temporal patterns of JE cases across regions were consistent with local antibody levels in the healthy population and the seasonal fluctuations of mosquito populations. It is necessary to strengthen surveillance and prediction and implement differentiated, precise prevention and control measures to reduce incidence.