Abortion caused by hemolytic disease associated with co-infection by Anaplasma marginale and Babesia spp. in dairy cattle.

Bovine anaplasmosis and babesiosis are important tick-borne diseases associated with significant economic losses, although fetal infection and abortion are rarely described. This study reports a bovine abortion associated with co-infection by Anaplasma marginale, Babesia bovis and Babesia bigemina. in the Midwestern region of Brazil. Fetal necropsy was performed, followed by cytological, histopathological, immunohistochemical, and molecular analyses. Gross findings included jaundice, splenomegaly, hepatomegaly, and renal discoloration, consistent with severe hemolytic disease. Blood smear evaluation revealed intraerythrocytic inclusions compatible with (A) marginale and Babesia-like merozoites, and PCR confirmed (B) bovis and B. bigemina, and Anaplasma spp. infection was confirmed by sequencing. Histologically, lesions consisted of erythrophagocytosis, hemosiderosis, hemoglobin casts, and marked intravascular leukocytostasis in multiple organs. Immunohistochemistry demonstrated accumulation of macrophages and T lymphocytes, suggesting activation of a fetal inflammatory response. These findings emphasize the importance of including hemoparasitic infections in the differential diagnosis of bovine abortion and support a role for fetal immune responses in lesion development.