Fumagillin is primarily used as an antiprotozoal agent, especially in the treatment of microsporidiosis, a parasitic infection that affects immunocompromised individuals such as those with HIV/AIDS. It works by inhibiting the growth of microsporidia by targeting their metabolic pathways. In veterinary medicine, fumagillin has been used to control nosema infections in honeybees, helping to protect bee colonies from collapse due to parasitic infestations. Additionally, it has shown potential in research settings for its anti-angiogenic properties, meaning it can inhibit the formation of new blood vessels, which is being explored in studies related to cancer and other diseases involving abnormal vascular growth. However, its clinical use is limited due to potential toxicity, particularly with long-term exposure.