After the 1990 floods in the coastal Brazilian city of Recife, 8/156 (5.1%) hospitalized AKI cases with thrombocytopenia were originally considered as leptospirosis, but were IFA-positive with R22, by HDPA based on HTNV 84/105, and were IgM-positive by ELISA, suggesting recent SEOV infections. Here, CD40LG is linked to leptospirosis.