In areas where PRNTs are not performed, positive dengue and negative Zika virus IgM antibody tests should be interpreted as a “presumptive recent dengue virus infection,” positive Zika and negative dengue virus IgM antibody tests should be interpreted as a “presumptive recent Zika virus infection,” and positive dengue and Zika virus IgM antibody tests should be interpreted as a “presumptive recent flavivirus infection.” If only one IgM antibody test was performed and was positive and PRNT was not performed, the second IgM test should be performed. Here, CD40LG is linked to Zika virus infectious disease.