The immune response to hookworm is complex and variable, but studies on Necator americanus hookworm infections in naive healthy human volunteers have revealed eosinophilia, parasite-specific IgG and IgE and secretion of both Th1 [interferon (IFN)-γ and tumour necrosis factor (TNF)-α] and Th2 [interleukin (IL)-5 and IL-13] cytokines (Maxwell et al., 1987; Wright and Bickle, 2005; Geiger et al., 2008). The gene discussed is IL5; the disease is ancylostomiasis.