Here, we found that both the newly developed BLACKBOX CCHFV IgM ELISA (employing recombinant CCHFV NP) and the VectoCrimean-CHF-IgM test readily detected CCHFV specific IgM antibodies in all samples collected after day 4 after onset of symptoms corresponding to a sensitivity of 100% when compared to the in-house gold standard CCHFV IgM IIFT. This evidence concerns the gene CD40LG and congestive heart failure.