Serological evidence of continued Japanese encephalitis virus transmission in Singapore nearly three decades after end of pig farming

Grace Yap,Lee Ching Ng,Xiao Fang Lim,Chiharu Okumura,Mahathir Humaidi,Yee Ling Lai,Sharon Chan,Choon Beng How,Marcella Kong,Diyar Mailepessov,Gladys Yeo

doi:10.1186/s13071-019-3501-0

Abstract

BackgroundSingapore used to report an annual average of 14 cases of Japanese encephalitis, but ever since the abolishment of pig farms in the early 1990s, the local incidence rate for Japanese encephalitis virus (JEV) infections has reduced drastically. Studies done in the early 2000s demonstrated the presence of JEV-specific antibodies in animals such as wild boars, dogs, chickens and goats on the offshore island and peripheral parts of the Singapore, indicative of prior JEV exposure. A JEV wildlife and sentinel chicken surveillance system was initiated in 2010 through to 2017 to study the animal host seroprofiles.ResultsA total of 12/371 (3.23%) of resident bird samples, 24/254 (9.45%) of migratory bird samples and 10/66 (15.16%) of wild boar samples were positive for the presence of JEV antibodies. Seroconversions in sentinel chickens were observed at two time points. Through this study, two sites with active transmission of JEV amongst avian or porcine hosts were identified.ConclusionsJEV transmission in animal hosts has continued despite the phasing out of pig farming nearly thirty years ago; however, the public health risk of transmission remains low. Environmental management for mosquito population remains key to keeping this risk low.

Highlights

Singapore used to report an annual average of 14 cases of Japanese encephalitis, but ever since the abolishment of pig farms in the early 1990s, the local incidence rate for Japanese encephalitis virus (JEV) infections has reduced drastically
A total of 371 donor bird sera were screened for JEV antibodies by immunofluorescence assay (IFA), followed by the confirmation of neutralizing antibodies by plaque reduction neutralization assay (PRNT)
A total of 254 plasma samples were collected from migratory birds which included plovers and common redshanks (Tringa tetanus)

Summary

Introduction

Singapore used to report an annual average of 14 cases of Japanese encephalitis, but ever since the abolishment of pig farms in the early 1990s, the local incidence rate for Japanese encephalitis virus (JEV) infections has reduced drastically. Studies done in the early 2000s demonstrated the presence of JEV-specific antibodies in animals such as wild boars, dogs, chickens and goats on the offshore island and peripheral parts of the Singapore, indicative of prior JEV exposure. Singapore used to report an annual average of 14 cases of JEV until the abolishment of pig farms in 1992 [6,7,8,9,10,11]. After 1992, the local incidence of JEV infections reduced drastically. JEV-specific antibodies were detected in animals such as wild boars, dogs, chickens

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