piroplasms

Piroplasms are small protozoan parasites of the order Piroplasmida within the phylum Apicomplexa. They are intraerythrocytic parasites, most commonly members of the genera Babesia and Theileria, which cause piroplasmosis in a range of vertebrate hosts. Transmission is tick-borne, with ixodid ticks serving as vectors; the parasites complete part of their life cycle in the tick and part in the vertebrate host.

Life cycle and biology: sporozoites transmitted by tick saliva invade red blood cells (Babesia) or leukocytes (Theileria). Babesia species reproduce inside erythrocytes by binary fission, producing merozoites that infect additional RBCs; Theileria species undergo transformation of lymphocytes to schizonts before merozoite production; sexual stages occur in ticks with transstadial transmission.

Clinical features and hosts: In animals, piroplasmosis often causes fever, anemia, hemoglobinemia or hemoglobinuria, icterus, and variable mortality, with cattle, sheep, goats, dogs, and other species affected depending on the parasite. In humans, Babesia species such as B. microti can cause babesiosis, presenting with fever, malaise, myalgia, and hemolytic anemia; severe disease can occur in splenectomized or immunocompromised individuals, sometimes requiring transfusion.

Diagnosis and treatment: Diagnosis relies on detection of intraerythrocytic piroplasms on Giemsa-stained blood smears, supplemented by PCR and serology. Treatments vary by host and agent: diminazene or imidocarb in animals; in humans, atovaquone with azithromycin or clindamycin with quinine; severe cases may require supportive care and, rarely, exchange transfusion. Tick control is important for prevention.

Epidemiology and significance: Babesia and Theileria have wide geographic distribution in temperate and tropical regions. Babesiosis is a zoonotic concern in areas with competent tick vectors and, occasionally, transfusion-associated transmission. Theileriosis primarily affects livestock, with economic impact in affected regions.