(also Babesiidae), a family of protozoans assigned to the class Sporozoa or the class Sarcodina (depending on the recognition or nonrecognition of their capacity for sexual reproduction in the bodies of ticks). The protozoans parasitize the red blood cells of cattle, horses, asses, swine, dogs, rats, and other mammals. Ticks are the carriers of Piroplasmidae. The protozoans reproduce asexually by division or budding in the blood cells. Upon entering the body of the tick with blood, the organisms reproduce and then embed themselves in the ovum. In this way transovarial transmission of the protozoans to ticks of the next generation occurs. In the second-generation ticks the parasites are localized in various tissues, including the salivary glands. When the infected ticks suck vertebrate blood, they transmit Piroplasmidae to the vertebrate.
The family Piroplasmidae includes the genera Babesia (or Piroplasma), Babesiella (or Microbabesia), and Nuttallia. Representatives cause serious diseases in animals, including piroplasmidoses, babesiases, and nuttalliases.