However, since WNV IgM can persist in serum for months and even years after infection (Prince et al., 2005; Busch et al., 2008; Murray et al., 2010, 2013; Papa et al., 2011, 2015) and significant cross reactivity exists between all flaviviruses it is often difficult to diagnose acute WNV infection based on these commercial kits alone. Here, CD40LG is linked to infection.