Nosema (microsporidian)

Nosema is a genus of microsporidian parasites. The genus, circumscribed by Swiss botanist Carl Nägeli in 1857, contains 81 species. Most parasitise insects and other arthropods, and the best-known Nosema species parasitise honeybees, where they are considered a significant disease by beekeepers, often causing a colony to fail to thrive in the spring as they come out of their overwintering period. Eight species parasitize digeneans, a group of parasitic flatworms, and thus are hyperparasites, i.e., parasites of a parasite.