In addition, host factors are of importance: these include age (children at higher risk than adults), ethnicity (white people at higher risk than black people), chronic diseases (bronchial asthma, diabetes mellitus, sickle cell anemia), nutritional status, sex and the individual’s genetic composition (allelic variants of genes that encode cellular receptors such as DC-SIGN and FcγRIIA, Vitamin D receptor as well as molecules involved in the antigen recognition, HLA, and cytokines have also been associated with higher or lower risk of DHF) [85–91]. This evidence concerns the gene CD209 and sickle cell disease.