A Special Insight on the Causal Agents and Mode of Occurrence of Japanese Encephalitis (JE) Infections in Rural Regions of Assam, India.

Abstract

Introduction: Japanese Encephalitis (JE) is a life-threatening disease, especially in the Indian subcontinent. Knowledge about the nature and ecology of the dispersal of JE virus (JEV) vectors needs to be increased. This study mechanistically explores the ecology of JEV vectors and the mode and frequency of occurrence of Acute Encephalitis Syndrome (AES) and JEV infections.

Methods: We established a linear relationship between environmental variables and JEV infection by JEV vectors (mosquitoes)-Culex tritaeniorhynchus, Culex vishnui, and Culex pseudovishnui. The relative abundance of three mosquito species was evaluated, and the JE Sample Positivity Rate (SPR) and JE Case Fatality Rate (CFR) were computed.

Results: Culex vishnui had a high abundance in residential areas during the transition from hot-dry (77.34%) to hot-wet period (78.66%) at temperatures between 31°C and 34°C and relative humidity of 80%-85.3%; this period also coincided with occurrence of AES (39 cases in hot-dry and 88 cases in hot-wet period) and JE (8 instances in hot-dry and 31 cases in hot-wet period). JE infection dominated near rainfed rice fields (rainfall: R = 0.67 at p < 0.05; rainy days: R = 0.74, p < 0.01). SPR was up to 32.28%, and CFR was as high as 42.86%; JEV infection was concentrated in adult male humans near rice fields (15.66%).

Conclusions: Climate modulation over the years can influence the distribution of Culex vishnui and, hence, AES and JE cases. JEV infections tend to rise in JE hotspot regions, especially near rice fields. Thus, comprehensive epidemiological investigations will help prevent a silent outbreak of JE.