Researchers developed a new test to detect Aspergillus fungal infections using an antibody that recognizes a fungal component called GAG. The test worked very well in mouse studies, reliably detecting the fungus in blood and other body fluids. However, when tested with samples from infected patients, the test could not find GAG in the blood or other fluids, though it could see the fungus in lung tissue. This suggests either patients don’t produce enough GAG in their bloodstream, or something in human biology interferes with detection.