Epidemiology of Japanese encephalitis in the Philippines: a systematic review

Japanese 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. We 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. We 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. This 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.