In addition, it is well-recognized that IgM following JEV infection can be detectable for months or years, so there is sometimes uncertainty when JE IgM is detected in serum whether it truly reflects JEV as the cause of a patient’s presentation or could be persisting IgM following a previous asymptomatic infection or mild febrile illness unrecognized as JE. This evidence concerns the gene CD40LG and infection.