 The clinical testing of the Na-ASP-2 Skin Test Reagent to detect Immediate-type hypersensitivity to the Na-ASP-2 hookworm antigen will be conducted as part of a larger, on-going observational study of the prevalence and intensity of hookworm infection currently underway in Brazil. Eligible adult participants ages 18-45 years in this observational study will be invited to undergo the skin testing procedure. Skin testing will only be performed if they agree and sign the supplemental informed consent form for this skin testing procedure. 