IgM seroneutralisation for improved confirmation of Japanese encephalitis virus infection in a flavivirus endemic area
Bharucha T., Ayhan N., Pastorino B., Rattanavong S., Vongsouvath M., Mayxay M., Changthongthip A., Sengvilaipaseuth O., Phonemixay O., Zitzmann N., Newton P., de Lamballerie X., Dubot-Pérès A.
Background: The mainstay of diagnostic confirmation of acute Japanese encephalitis (JE) involves detection of anti-JEV IgM by ELISA. Limitations in the specificity of this test are increasingly apparent with the introduction of JEV vaccinations and the endemicity of other cross-reactive flaviviruses. Virus neutralisation testing (VNT) is considered the gold standard but is challenging to implement and interpret. We performed a pilot study to assess IgG depletion prior to VNT for detection of anti-JEV IgM neutralising antibodies, 'IgM-VNT' as compared to standard VNT. Methods: We evaluated IgM-VNT in paired sera from anti-JEV IgM ELISA positive patients (JE n=35) and negative controls of healthy flavivirus naïve (n=10) as well as confirmed dengue (n=12) and Zika virus (n=4) patient sera. IgM-VNT was subsequently performed on single sera from additional JE patients (n=76). Results: Anti-JEV IgG was detectable in admission serum of 58% of JE patients. The positive, negative and overall percentage agreement (PPA, NPA, OPA) of IgM-VNT was 100%. 12/14 (86%) patient samples unclassified by VNT, and with sufficient sample available for IgG depletion and IgG ELISA confirming depletion were classified by IgM-VNT. IgM-VNT enabled JE case classification in 72/76 (95%) of the patients for whom only a single sample was available. Conclusions: The novel approach has been readily adapted for high-throughput testing of single patient samples, and it holds promise for incorporation into algorithms for use in reference centres.