Among the measles-rubella specimens, we identified 75 (%) with evidence of CHIKV infection by IgM, including 62 (%) confirmed by cross-neutralizing PRNT with detectable titers to CHIKV and not to ONNV among the samples tested probably because the samples were previously selected with an ELISA test considered specific for CHIKV. The gene discussed is CD40LG; the disease is measles.