Changing paradigm in the epidemiology of Japanese encephalitis in a non-endemic region

Area of Science:

• Epidemiology
• Virology
• Public Health

Background:

• Japanese encephalitis (JE) is a significant mosquito-borne zoonotic disease caused by the JE virus (JEV).
• JEV circulates asymptomatically in natural hosts, with transmission primarily occurring through mosquitoes of the Culex vishnui subgroup.
• Thanjavur district in Tamil Nadu was considered a non-endemic region for JE prior to this investigation.

Purpose of the Study:

• To investigate the prevalence of JEV in both mosquito vectors and the human population within the Thanjavur district.
• To assess the risk of JEV infection in children aged 5-12 years in a region not previously recognized as endemic.
• To identify potential factors contributing to JEV transmission dynamics.

Main Methods:

• A sero-surveillance study was conducted among rural school children (5-12 years) during JE and post-JE seasons (2011-2013).
• Vector abundance studies were performed from 2011 to 2014 to identify dominant mosquito species.
• Statistical analysis was used to compare JE seropositivity rates between seasons and historical data.

Main Results:

• High JE infection rates were observed in children aged 5-12 years, with rates of 32.2% in 2011-12 and 65.2% in 2012-13.
• Culex tritaeniorhynchus was identified as the dominant mosquito species and the primary vector responsible for transmission.
• A significant increase in human infection rates was noted compared to 1991-93, alongside a decrease in the cattle to pigs ratio.

Conclusions:

• The study highlights a concerning prevalence of JE among children, particularly during the transmission season.
• A reduced cattle to pigs ratio may be a contributing factor to the increased JEV infections observed over two decades.
• Urgent implementation of effective surveillance systems and vaccination strategies is crucial to prevent JE outbreaks.