Diagnosis of human infection is not easy, and is based upon: (1) the presence or absence of antiviral IgM (as measured in IgM antibody capture-ELISA, MAC-ELISA) in acute-phase serum or cerebrospinal fluid (CSF) specimens; (2) a virus-specific four-fold or higher IgG titer rise or fall from acute- to convalescent-phase paired serum specimens; and/or (3) direct demonstration of infectious virus, viral antigen, or viral RNA in serum, CSF, or tissue specimens. This evidence concerns the gene CD40LG and infection.