Baruah Aditya, Hazarika Razibuddin A, Barman Nagendra N, Islam Saidul, Gulati Baldev R
Department of Veterinary Public Health, College of Veterinary Science, Assam Agricultural University, Guwahati, Assam, India.
Department of Veterinary Microbiology, College of Veterinary Science, Assam Agricultural University, Guwahati, Assam, India.
J Vector Borne Dis. 2018 Oct-Dec;55(4):291-296. doi: 10.4103/0972-9062.256564.
BACKGROUND & OBJECTIVES: Assam is the most vulnerable state for Japanese encephalitis (JE) in India. The situation warrants characterization of epidemiological patterns of JE in vectors, pigs and human population. This investigation was aimed to determine the relative abundance of mosquito species and seroprevalence of JE in pigs in order to draw an epidemiological association with reported human JE cases in Assam.
Pig sera and mosquitoes from selected farms in Sivasagar and Kamrup districts of Assam were collected fortnightly for one year during June 2015-May 2016. Pig sera were tested for JE antibodies by haemagglutination and virus neurtralization tests. Mosquito species were identified microscopically following the taxonomic keys. The results were analyzed with data on confirmed human JE cases in the selected districts.
Culex gelidus (26.07%) and Cx. tritaeniorhynchus (24.07%) were the most abundant species in collected mosquitoes (n = 997). A total of 22.99% of pigs (n = 335) were JEV seropositive and 45.65% of human acute encephalitis syndrome cases (n = 230) were positive for JE virus (JEV) infection. Relative mosquito abundance, pig positivity and human cases were highest during monsoon (June-September) and least during winter (December-February). Rise in mosquito population was observed during pre-monsoon season (March-May) and concurrently higher number of human cases and pig seropositivity were recorded. A good correlation was observed between mosquito number and JEV positivity in pigs/human, and between pigs and human cases (p < 0.05). Human population in Sivasagar was at higher risk for JE infection (OR: 6.46, p < 0.0001) than in Kamrup rural district.
INTERPRETATION & CONCLUSION: This study indicates that a seasonal correlation exists between mosquito abundance and JEV seroconversion in pigs with concurrent human JEV outbreaks under field conditions in Sivasagar and Kamrup rural districts of Assam and that monitoring mosquito abundance/density and pig JEV seropositivity may help in predicting JEV outbreak in human population in the region.
阿萨姆邦是印度日本脑炎（JE）疫情最脆弱的邦。这种情况需要对媒介、猪和人群中JE的流行病学模式进行特征描述。本研究旨在确定蚊虫种类的相对丰度以及猪群中JE的血清阳性率，以便与阿萨姆邦报告的人类JE病例建立流行病学关联。
在2015年6月至2016年5月期间，每两周从阿萨姆邦锡瓦萨加尔和卡姆鲁普地区选定的农场采集猪血清和蚊虫样本，为期一年。通过血凝试验和病毒中和试验检测猪血清中的JE抗体。按照分类学检索表在显微镜下鉴定蚊虫种类。将结果与选定地区确诊的人类JE病例数据进行分析。
在采集的蚊虫（n = 997）中，环纹库蚊（26.07%）和三带喙库蚊（24.07%）是数量最多的种类。共有22.99%的猪（n = 335）JE病毒血清学阳性，45.65%的人类急性脑炎综合征病例（n = 230）JE病毒（JEV）感染呈阳性。蚊虫相对丰度、猪的阳性率和人类病例数在季风季节（6月至9月）最高，在冬季（12月至2月）最低。在季风前季节（3月至5月）观察到蚊虫数量增加，同时记录到更高的人类病例数和猪的血清阳性率。在蚊虫数量与猪/人类的JEV阳性率之间，以及猪与人类病例之间观察到良好的相关性（p < 0.05）。锡瓦萨加尔的人群感染JE的风险（比值比：6.46，p < 0.0001）高于卡姆鲁普农村地区。
本研究表明，在阿萨姆邦锡瓦萨加尔和卡姆鲁普农村地区的野外条件下，蚊虫丰度与猪的JEV血清转化之间存在季节性相关性，同时伴有人类JEV疫情爆发，监测蚊虫丰度/密度和猪的JEV血清阳性率可能有助于预测该地区人群中的JEV疫情。
