Fumagillin is an antibiotic originally used against fungal Nosema apis infections in honeybees. Some studies found it to be effective against some myxozoan parasites, including Myxobolus cerebralis, an important parasite of fish; however, in the more rigorous tests required for U.S. Food and Drug Administration approval, it was ineffective. Fumagillin can block blood vessel formation by binding to an enzyme called methionine aminopeptidase 2.