Family Babesiidae is a group of small parasitic protozoans that infect the red blood cells of many mammals, including domestic animals and humans. The family is also known by various synonyms, including the Theileriidae, Nuttalliellidae, and Haemogregarinidae families. Some species of Babesiidae can cause severe disease in animals and humans, including babesiosis, a malaria-like illness. These parasites are typically transmitted by ticks, and symptoms of babesiosis can include fever, anemia, and muscle pain. For animals, Babesiidae infections can lead to decreased milk production, weight loss, and sometimes death. The diagnosis and treatment of Babesiidae infections are important for the health of both animals and humans.