Research Article: Epidemiology of Japanese Encephalitis in the Philippines: A Systematic Review

Date Published: March 20, 2015

Publisher: Public Library of Science

Author(s): Anna Lena Lopez, Josephine G. Aldaba, Vito G. Roque, Amado O. Tandoc, Ava Kristy Sy, Fe Esperanza Espino, Maricel DeQuiroz-Castro, Youngmee Jee, Maria Joyce Ducusin, Kimberley K. Fox, Maya Williams.

Abstract: BackgroundJapanese encephalitis virus (JEV) is an important cause of encephalitis in most of Asia, with high case fatality rates and often significant neurologic sequelae among survivors. The epidemiology of JE in the Philippines is not well defined. To support consideration of JE vaccine for introduction into the national schedule in the Philippines, we conducted a systematic literature review and summarized JE surveillance data from 2011 to 2014.MethodsWe conducted searches on Japanese encephalitis and the Philippines in four databases and one library. Data from acute encephalitis syndrome (AES) and JE surveillance and from the national reference laboratory from January 2011 to March 2014 were tabulated and mapped.ResultsWe identified 29 published reports and presentations on JE in the Philippines, including 5 serologic surveys, 18 reports of clinical cases, and 8 animal studies (including two with both clinical cases and animal data). The 18 clinical studies reported 257 cases of laboratory-confirmed JE from 1972 to 2013. JE virus (JEV) was the causative agent in 7% to 18% of cases of clinical meningitis and encephalitis combined, and 16% to 40% of clinical encephalitis cases. JE predominantly affected children under 15 years of age and 6% to 7% of cases resulted in death. Surveillance data from January 2011 to March 2014 identified 73 (15%) laboratory-confirmed JE cases out of 497 cases tested.SummaryThis comprehensive review demonstrates the endemicity and extensive geographic range of JE in the Philippines, and supports the use of JE vaccine in the country. Continued and improved surveillance with laboratory confirmation is needed to systematically quantify the burden of JE, to provide information that can guide prioritization of high risk areas in the country and determination of appropriate age and schedule of vaccine introduction, and to measure the impact of preventive measures including immunization against this important public health threat.

Partial Text: Japanese encephalitis (JE) is a vector-borne disease that is endemic in most of Asia. Worldwide, it is estimated that around 68,000 cases occur annually, 40,000 in the Western Pacific Region alone. Most of these cases in endemic countries occur among children under 15 years of age, as adults are often already immune to the disease. JE is a significant public health threat, with case fatality rates of up to 30% and long-term neuropsychological sequelae in 30–50% of its survivors [1]. Because of the absence of treatment for JE and recent expansion of the geographic range of the disease, the World Health Organization (WHO) has recognized the exigency of improved surveillance for JE and recommended the integration of JE vaccine into routine immunization programmes wherever JE constitutes a public health problem. Vaccination is considered the single, most important control measure for JE [2].

We identified 29 articles and presentations on JE in the Philippines (Fig. 1). Five articles published from 1958 to 1993 reported on JE serologic surveys conducted in various areas of the country (Table 1). The first serologic survey in JE in the Philippines was conducted by Hammon, et al, using the suckling mouse neutralization test (NT) [3]. In 1964, Basaca-Sevilla and Halstead included nine serological studies conducted in the Philippines that identified JE antibodies using HI, CF or NT in their review, suggesting the circulation of JEV in the country [7].

This systematic review of JE data confirms the endemicity of JE in the Philippines and its broad distribution across the country. Based on seroepidemiologic and clinical JE infection studies, animal and mosquito surveys, and surveillance data, JEV has been documented in Metro Manila and in 32 provinces located in all regions of the country and suspected JE cases have been reported in 68 of the 81 provinces and major cities of the country. Mapping of available data on JE in the country suggests that the disease is widespread.



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