Laboratory-based Japanese Encephalitis Surveillance in Nepal and the Implications for a National Immunization Strategy

Abstract

We report on two years of Japanese encephalitis (JE) surveillance in Nepal and the implications for a national immunization strategy. From May 2004 to April 2006, 4,652 patients with encephalitis were evaluated. A serum or cerebrospinal fluid specimen was collected from 3198 (69%) patients of which 1,035 (32%) were positive by Japanese encephalitis IgM ELISA. Most cases (N = 951, 92%) were from the 24 Terai districts (i.e., southern plains, 12.3 million persons) with the majority (N = 616, 65%) from four western Terai districts (population = 1.8 million). The case fatality ratio was 14.7% and 6.3% and the proportion of cases under 15 years old was 52% and 62% in the four western and 20 non-western Terai districts, respectively. Japanese encephalitis immunization targeting residents one year of age and older in the western districts and one through 14 years old in the non-western Terai districts may have reduced Japanese encephalitis cases by 84% and deaths by 92%, nationally.

Hospital-Based Surveillance for Japanese Encephalitis at Four Sites in Bangladesh, 2003–2005

“…In Nepal, the age group affected also included young adults and adults and may have been caused by migration of working people from non-endemic areas to endemic areas. 27 All JE infections were identified during May-December, with 90% identified during May-October. The assessment of JE prevalence in Sylhet in northeastern Bangladesh was limited because patients were only enrolled from December 2004 through July 2005 and this period was only three months of a single JE transmission season.…”

Estimated global incidence of Japanese encephalitis:

“…Each of these papers (or the English translation of five Chinese-language papers) was then carefully reviewed by at least two authors to further cull the list, resulting in a final group of 12 studies that provided original, recent population-based and largely laboratory-confirmed incidence data (or hospital-based incidence data in a defined population). 13,20,[23][24][25][26][27][28][29][30][31][32] These 12 studies consisted of one study each from Bangladesh, Cambodia, Indonesia, Malaysia and Thailand, two from China (excluding Taiwan) two from Japan and three from Nepal. They represented all but three (B, E and I) of the 10 incidence groups (Table 1).…”

“…• Incidence Group G: Overall incidence is 1.0 per 100 000 (approximate weighted average of results from three studies from Nepal 28,29,31 and one study from Bangladesh 30 ); the child to adult case frequency ratio is 4:1 (based on the ratio of 73 cases in 0-14-year-olds to 17 cases in persons aged > 14 years, per the table in the report by Bhattachan and colleagues 31 ).…”

Estimation of the Impact of a Japanese Encephalitis Immunization Program with Live, Attenuated SA 14-14-2 Vaccine in Nepal

“…AES/JE surveillance was strengthened in 2004 with designation of 45 medical facilities as sentinel sites, enhanced case-based surveillance using a standardized case definition, improved access to JE laboratory testing, and use of the infrastructure developed for polio surveillance. 16 The initial 45 sentinel sites consisted of 34 sites in 20 of 24 Terai districts and 11 sites in 5 hill districts. The AES/ JE surveillance system was expanded to additional sites in subsequent years.…”