Mcpt4−/− mice showed ↓ parasitemia, ↑ intestinal permeability, early ↑ ileal mast cells and IgE, altered E‐cadherin/ZO‐1 junctions, ↓ neutrophil MPO activity, early Type‐1 cytokine bias (↑IL‐12p40, TNF‐α) vs. Type‐2 bias (↑IL‐10, IL‐4) in WT; despite reduced parasitemia, ↑ transmission to A. stephensi. The gene discussed is MPO; the disease is parasitic infectious disease.