Serological diagnosis is complicated by extensive cross-reactivity between anti-DENV and ZIKV immunoglobulin M/ immunoglobulin G (IgM/IgG) antibodies.4, 5, 6, 7 Antibodies produced in primary infection tend to have higher specificity compared to those produced in secondary infections, further reducing the utility of serology tests for the diagnosis of flavivirus infections in areas where these infections are endemic.4, 5, 6, 7 A systematic review showed that about 15–84% of antibodies produced against non-DENV flaviviruses were cross-reactive with those of DENV on different assays.8 This evidence concerns the gene CD40LG and infection.