New Elisa Test Based on Recombinant Antigen for the Differenciation of Japanese Encephalitis Virus and West Nile Virus Antibodies

Context: Japanese Encephalitis (JEV) virus and West Nile virus (WNV) which belong to the Japanese flavivirus serocomplex are mosquito-borne viruses that can elicit clinical signs of encephalitis in humans and horses. WNV is widely distributed worldwide while JEV is widespread in Eastern and Southern Asian countries. The available ELISA tests for flavivirus diagnosis that are mainly based on inactivated native antigens or recombinant prM/E proteins remain poorly informative regarding the identification of infecting pathogen due to the cross-antigenic reactivity between neurotropic flaviviruses including WNV and JEV. The ectodomain of flavivirus E protein folds into 3 antigenic domains, the central domain I and two strongly immunogenic domains, DII and III, the latter (EDIII) exhibiting a variability that differentiates antigenically the members of a same flavivirus serocomplex.

Objectives: Using the Drosophila expression system, highly purified recombinant EDIII (rEDIII) from JEV and WNV have been produced at the Pasteur Institute. Indirect ELISA tests using a panel of horse and pig antisera to WNV and JEV were performed to assess the antigenicity of rEDIII and their ability to differentiate the antibodies specific to WNV or JEV.

Results: Sensitivity and specificity of these ELISA tests were evaluated, and were found to be respectively 90% for sensitivity and over 98% for specificity. Moreover, this protocol allowed for a clear differentiation between WNV and JEV infection in 73% of 100 positive horses tested (WN positive antibodies and JEV negative antibodies), while this differentiation was found inconclusive for 26% positive horses (WN and JEV positive antibodies). 

Conclusion: Even if there is still some level of cross reactions between JEV and WNV antibodies observed with the newly developed ELISA, these results are encouraging.