1. A protozoan genus (family Nosematidae, order Microsporida, phylum Microspora) with species (Nosema apis, Nosema bombycis, and others) pathogenic for invertebrates of economic importance (bees, silkworms); others are being studied as possible agents of biologic control of pest insects or other target invertebrates. N. connori infects human fat tissue, diaphragm, myocardium, liver, and other tissues of immunosuppressed people.
The definition information for Nosema is provided by Stedman's. You can search our medical dictionary here.