Background: Japanese encephalitis virus (JEV) is the most common vaccine-preventable cause of encephalitis in Asia. Clinical symptoms vary from a mild non-specific febrile illness to severe encephalitis. However, the majority of JEV infections are asymptomatic, meaning most remain undetected. In Indonesia, JEV is presumed to be endemic in several provinces, but limited disease surveillance means no clinical case has ever been recorded in West Java. JEV surveillance is therefore critical for characterizing epidemiology, measuring disease burden, and documenting the impact of control measures.
Methods: Archived specimens were gathered from previous studies in West Java on hospitalized patients suspected of hantavirus infection (n = 406), and cases of suspected dengue from a cohort of adult factory workers (n = 737) and community clusters (n = 143). All available paired samples (n = 236) from non-dengue febrile cases were tested for anti-JE IgM using immunoglobulin M antibody capture ELISA (MAC-ELISA). Case definition for JE was relatively conservative, based on detection of IgM antibodies in convalescent sera samples (seroconversion) using a CDC reference assay.
Results: Preliminary testing of 253 samples showed 2 JEV-positive cases, one adult and one child. Both cases were from systemic febrile illnesses with fever and headache but no neurological manifestations. Cell culture and RT-PCR were also attempted without positive results. The acute sera (day 2) of both cases were negative but both convalescent sera (day 11) tested positive for JE IgM. Hematological investigations showed no hemoconcentration, thrombocytopenia or leucopenia.
Conclusions: Although there are a number of laboratory tests to diagnose JEV infection, virus detection assays are not useful for diagnostic purposes due to low-level, transient viremia. We may have documented more seroconversions if there were more appropriately timed convalescent samples. This is the first reported case of JEV as the cause of non-encephalitic illness in Java, as JE is not usually in the diagnostic algorithm for febrile illnesses. Our study also suggests that JE surveillance in non-encephalitic cases might contribute towards the true epidemiology of JE disease in humans, which is based primarily on acute encephalitis syndrome.