Furthermore, this diagnostic approach not only opens up the possibility of screening for symptomatic and asymptomatic L. (L.) infantum chagasi-infection in endemic areas (urban or rural) but also of monitoring the evolution of their clinical-immunological profiles of infection in any of the epidemiological scenarios involved—making it possible to diagnose and treat early cases (III profile) with genetic susceptibility (IgM reactors) before they evolve into severe form (SI profile = AVL) of infection. The gene discussed is CD40LG; the disease is infection.