European Preparedness for Japanese Encephalitis Virus Through Alignment of Animal Health Laboratory Diagnosis

Abstract

Outbreaks of Japanese encephalitis (JE) can have severe health and economic impacts in both humans and susceptible animal species and are estimated to cause ~68,000 human disease cases in Asia annually. The disease is caused by infection with the mosquito-borne JE virus (JEV), which continues to expand its geographical range from its endemic region in Asia. Since appropriate vertebrate host and mosquito vector species are present in Europe and average European summer temperatures continue to increase, JEV introduction could lead to the establishment of the pathogen in native mosquito species and wild birds and disease outbreaks among humans, pigs, and horses. Incursions could occur through movements of infected pigs and mosquitoes but also via migratory birds that act as reservoirs. Introduction and establishment of JEV in these populations may not be apparent at first, providing time for virus spread before spillover to the human population. Further complicating serological detection of JEV is the extensive cross-reactivity with other orthoflaviviruses circulating in Europe (i.e., tick-borne encephalitis virus [TBEV], West Nile virus [WNV], and Usutu virus [USUV]). In addition, viremia in clinical cases may be short, hindering virus detection. To facilitate European preparedness for detection, surveillance, and monitoring of JEV introduction and spread, five veterinary national reference laboratories in Europe collaborated with the aim to align JEV diagnostic pipelines to prepare for future emergence of JEV in Europe. All institutes assessed established and newly developed serological and molecular assays to build capability with sensitive and specific diagnostic tools for JEV detection. Additionally, methods for whole-genome sequencing (WGS) were established and compared. In summary, this project provides a framework for communication and international collaboration between arboviral researchers at national veterinary institutes. The sharing of knowledge and expertise, and alignment of diagnostic techniques, has facilitated improvement of diagnostic pipelines for JEV detection and contributed to preparedness for JEV introduction into Europe.

Keywords: Japanese encephalitis; diagnostics; emerging; orthoflavivirus; zoonosis.

Figure 1

Transmission cycles of Japanese encephalitis virus in endemic and enzootic areas, highlighting the impact of climate changes (increased temperature and rainfall) on the risk of virus outbreaks, and the potential involvement of wild boar. Created with BioRender.com. Mansfield, K. (2025) https://BioRender.com/n6xdcp3.