Sero-Epidemiology of Japanese Encephalitis in Nepal

Abstract

Japanese encephalitis (JE) is one of the major public health problems in Nepal becauseof its increasing disease morbidity and mortality.In 2005, a total of 2952 cases of acuteencephalitic syndrome (AES) were reported with a peak(76.4%) during 31-38epidemiological weeks in the range of 92 to 498 cases per week. Among 58 AES casesreporting districts, the highest no. were reported from Kailali (435, 14.7 %) followed byDang, Bardiya, Kathmandu, Banke, Kachanpur, Kapilvastu, Nawalparasi and Sunsari.These 8 districts reported more than 50 % cases. The highest no. of AES cases (839,28.4 %) were recorded from MWDR.Only 2239 specimens (serum/CSF) could be collected and tested by MAC ELISAtechnique, of which 723 (32.3%) were found positive for anti-JEV IgM. Also, 235clinically defined AES cases showed anti-JEV IgM in the range of 20 to <40 unitswhich may be doubtfull/equivocal.Among positive cases, 420 (58.1 % of total JE positives) were male and 303 (41.9 %)were female. The ratio of JE cases in male to female was observed as 1.4:1. Themajoritypositive cases (58.9 %) were from the age group below 15 yearsthan fromabove 15 years. Age group 5-15 years showed both the highest no. of positive cases(41.2 %) and sero-positivity (36 %).JE cases started increasing from May and reached a peak during September (436, 60.3%) and dropped then after. Sero-positivity rate was also highest in themonth ofSeptember (42.1 %).Among 41 districts, the highest no. of positive cases were detected in Bardiya (15.4 %)followed by Kailali (14.7 %), Banke (13.3 %) and Dang (12.3 %). These 4 districtsaccounted for 55.7 % of the total positives. The highest no. of positive cases (314, 43.4%) were detected from MWDR followed by FWDR (130, 18 %). Geographically, terai region (20 districts) reported 75.6 % (2232) of total AES cases and 85.1 % (615) oftotal JE positives.In 2005, 322 deaths due to AES were recorded with the CFR and CI of 10.9 % and 12.9per10 5 population respectively. Among positive cases, 43 died and CFR of 5.9 % andCI (3.2/10 5 ) were reported. The highest CFR (8.9 %) and CI (5.1) for JE positive caseswere found in the age groups above 15years and 5-15 years respectively. CI washighest in Bardiya (65.1) district followed by Kailali (63.5), Dang (60.1), Banke (51.6)and Kanchanpur (35.7). CFR was highest in WDR (15.2 %) followed by FWDR (14.5%) and CI was highest in FWDR (39.1) followed by MWDR (31.5). The actual JEburden can be estimated by strengthening and expanding the diagnostic facilities in thecountry. Continuation of active surveillance, vector control measures and expandedprogramme of immunization (EPI) in JE endemic areas should be strongly emphasizedto reduce the endemicity of disease.