IFNG and infection: Therefore, the Se and Sp of the IFN-γ assay are related to the tests adopted to define the “positive animal.” These parameters are calculated on the basis of tests applied at the different stages of infection, in animal producing antibodies against MAP and/or in animal shedding MAP, while the IFN-γ test reveals infected animals that generally do not yet produce antibodies and do not yet shed MAP in their feces.