Japanese Encephalitis Virus as Cause of Acute Encephalitis, Bhutan (original) (raw)

2020, Emerging Infectious Diseases

J apanese encephalitis virus (JEV), a mosquitoborne flavivirus, is a common cause of encephalitis in Asia (1). Japanese encephalitis (JE) causes considerable illness and death, particularly in children <15 years of age (2). No specific treatment exists, but JE is preventable by vaccination. JEV is maintained in an enzootic cycle between mosquitoes and amplifying vertebrate hosts, primarily pigs and wading birds (2). Culex mosquitoes are the principal vectors, especially Cx. tritaeniorhynchus, and commonly breed in rice fields and other stagnant water collections (2). JEV transmission occurs predominantly in rural agricultural areas (2). In Bhutan, JEV vectors are prevalent in many southern districts and in some interior districts. Five Culex mosquito species have been identified: Cx. tritaeniorhynchus, Cx. vishnui, Cx. pseudovishnui, Cx. gelidus, and Cx. quinquefasciatus. In particular, Cx. tritaeniorhynchus mosquitoes have been documented in the southern districts of Chukha, Samtse, Sarpang, and Samdrup Jonghkar. In much of the country, rice fields and other mosquito breeding sites are common (G.M. Yeshey et al., unpub. data, https://www.researchgate. net/publication/277224776_Effect_of_mineral_fertil-izers_on_rice_productivity_in_Punakha-Wangdue_ Valley), and pigs and wading birds can be found. At least 18,800 pigs were reported in Bhutan in 2017 and reared in centralized government breeding farms, with up to several hundred pigs, or in backyard farms, typically with <5 pigs (3,4). About two thirds of the country's ≈750,000 persons live in rural areas (5). In consideration of the favorable conditions for JEV transmission and proximity to other JE-endemic countries, in 2011, the Royal Centre for Disease Control, Ministry of Health, implemented surveillance to investigate JE presence among humans in Bhutan. The Surveillance Bhutan's landscape ranges from lowland plains in the south to the Himalayan mountains in the north (6). The climate varies with elevation: very cold yearround in the north, temperate in the midlands, and subtropical in the south. Monsoon season spans mid-July through September. Bhutan has 20 administrative districts each with >1 general hospital. The regional referral hospital in Sarpang district in the south serves the central region and the referral hospital in Mongar district in the east serves the eastern region. The national referral hospital in the capital Thimphu also serves as the regional referral hospital for the western region. The Royal Centre for Disease Control has conducted sentinel site-based JE surveillance at 5 sites since 2011: the national and 2 regional referral hospitals, Phuntsholing hospital in Chukha district in the southwest, and Samdrup Jongkhar hospital in Samdrup Jongkhar district in the southeast (Figure). The Royal Centre for Disease Control staff based surveillance case definitions on those from the World Health Organization (WHO) JE surveillance