Increasing seroprevalence of Japanese encephalitis virus in even-toed hoofed mammals (Artiodactyla species) associated with an upsurge of human cases in South Korea.

Objectives: The annual incidence of Japanese encephalitis (JE) has increased markedly in South Korea since 2010. We hypothesized that this increase was associated with higher frequencies of JE virus in animals.

Methods: We analyzed 5201 serum samples collected from even-toed hoofed mammals (Artiodactyla species) across South Korea from 2008 to 2012 using a stratified two-stage probability approach.

Results: The highest annual incidence of human JE cases and deaths occurred in 2010. Cases increased from six (no deaths) in 2008-2009 to 26 cases (seven deaths) in 2010. The JE virus seroprevalence in deer and elk fawns increased from 2.4% in 2008 to 24.1% in 2009, and in wild boars, it increased from 19.3% to 55.0% in the same period, which preceded the surge of human cases. Furthermore, the seroprevalence in calves increased from 15.3% in 2008 to 35.8% in 2010, and that in lambs and goat kids, increased from 8.5% in 2009 to 26.2% in 2010, which coincided with the surge in humans.

Conclusion: Our findings show that the increased incidence of human JE in South Korea was temporally associated with an increasing seroprevalence in the Artiodactyla species. Surveillance of sentinel animals may be useful to predict the emergence of JE in humans.