Seroconversion to Japanese Encephalitis Virus Among U.S. Infantry Forces in Korea

Abstract

Abstract. Japanese encephalitis virus (JEV) is endemic in the Republic of Korea (ROK), posing a medical threat to more than 29,000 U.S. Forces military personnel currently deployed in the ROK. The objective of this study was to provide data on the risk of JEV exposure among U.S. Forces in the ROK. One thousand U.S. Army Soldiers were randomly selected for the study from the cohort of infantry Soldiers deployed in the ROK for a period of at least 330 days from 2008 to 2011. Pre-and post-deployment serum specimens were tested for the presence of JEV antibodies by plaque reduction neutralization test. A total of 2/1,000 (0.2%) U.S. Army Soldiers post-deployment specimens tested positive for JEV antibody. Results from the pre-deployment specimens indicated one true seroconversion and one with titers suggestive of a JEV infection. These results indicate a low, but nonzero risk of JEV exposure among U.S. Army Soldiers in the ROK.Japanese encephalitis virus (JEV) infections can result in serious outcomes. The case fatality rate is reported to be between 20% and 30%, with 30-50% of the survivors having long-term neurologic and psychiatric sequelae that often lead to an early death.1 JEV is endemic in the Republic of Korea (ROK), with > 2,500 cases reported for years 1964 (966 deaths), 1966 (695 deaths), and 1967 (810 deaths). For this reason, the ROK government initiated a mandatory childhood National Immunization Program in 1967 that became fully established by 1983, when only 139 cases (12 deaths) were reported. 2,3From 1984 to 2009, there were only 0-7 cases reported annually as a result of the mandatory childhood vaccination policy. 2,3 However, even with these measures in place, JEV remains present in the mosquito populations, through zoonotic transmission, as indicated by outbreaks from 2010 to 2014 (89 cases, 18 deaths) (T. A. Klein, pers. comm.). 2,4The continued presence of JEV in the ROK poses a potential threat to the greater than 29,000 U.S. Forces military personnel deployed and greater than 13,000 beneficiaries (civilians and family members) who currently reside in the ROK. Historically, Department of Defense (DoD) policy only recommended, but did not require, JEV vaccination for service members visiting or deploying in the Pacific Command region, including the ROK, for more than 30 days or for short-term nonurban travel. 5,6 However, in 2015, the Air Force and U.S. Forces Korea began requiring JEV vaccinations for service members who will be in the ROK for 30 days or more. 7,8 During the Korean War (1950)(1951)(1952)(1953), there were 299 cases of confirmed/ suspected JE cases among U.S. service members during 1950 alone.9,10 JE has also been identified in vectors where U.S. Army personnel train and military installations throughout the ROK. For example, during 2010 there were more than 80 pools of Culex tritaeniorhynchus, the primary vector of JEV in the ROK, collected near the Demilitarized Zone that were positive for JEV Genotype I and one pool that was positive for Genotype V, which had not been repo...

‘More than devastating’—patient experiences and neurological sequelae of Japanese encephalitis§

“…The risk of developing JE in travellers is hard to determine. Asymptomatic infection is detectable but infrequent 25 , 26 . Disease incidence will be even lower—estimated in European travellers at one case per 5.4 million visits to Asia 27 .…”

Method Comparison for Japanese Encephalitis Virus Detection in Samples Collected from the Indo-Pacific Region

“…Forces Korea (Eick-Cost et al, 2015). They found that prevalence was as low as 0.2% of the population studied, and at least one soldier had titers high enough to indicate current or recent infection.…”

“…A 2015 study performed in the Republic of Korea tested the serum of 1,000 soldiers that had never previously deployed to determine the prevalence of JEV antibodies among personnel in the U.S. Forces Korea (Eick-Cost et al, 2015). They found that prevalence was as low as 0.2% of the population studied, and at least one soldier had titers high enough to indicate current or recent infection.…”

Method comparison for Japanese encephalitis virus detection in samples collected from the Indo-Pacific region

“…A 2015 study performed in the Republic of Korea tested the serum of 1,000 soldiers that had never previously deployed to determine the prevalence of JEV antibodies among personnel in the U.S. Forces Korea ( 17 ). They found that prevalence was as low as 0.2% of the population studied, and at least one soldier had titers high enough to indicate current or recent infection.…”