Nosema apis is a microsporidian, a small, unicellular parasite that mainly affects honey bees. It causes nosemosis, also called nosema, which is the most widespread of the adult honey bee diseases. The dormant stage of nosema is a long lived spore which is resistant to temperature extremes and dehydration. Nosema apis spores cannot be killed by freezing contaminated comb. Nosemosis is a listed disease with the Office International des Epizooties (OIE) .