University of Tabriz Journal of Zoonotic Diseases 2476-535X 10 3 2026 08 01 Immunopathology, reproductive effects, and diagnostic challenges of Toxoplasma gondii infection in large animals: A narrative review 1248 1266 22032 10.22034/jzd.2026.22032 EN Narges Lotfalizadeh Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran 0000-0003-4910-5498 Saeed Nazifi Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Journal Article 2026 05 24 In large animals, <em>Toxoplasma gondii</em> infection is usually primarily a reproductive disease rather than an overt systemic illness. It is a significant cause of abortion, stillbirth, and neonatal weakness in domestic animals. This review incorporates much of the available information on the biology of the parasite and the host immune system, reproductive outcomes, and the clinical pathology of toxoplasmosis in large animals. Following consumption of sporulated oocysts, a persistent infection is initiated through the development of a tissue cyst, and a Th1-type of immunity is considered to constrain the systemic disease seen in the adult host. However, the gestational immunomodulation leads to a hospitable environment at the maternal-fetal interface, permitting vertical transmission. The reproductive disease is characterized by necrotizing placentitis, vascular damage, and fetal tissue damage, depending on the stage of gestation. There are usually minor and variable clinical pathologic alterations in adults. Therefore, blood testing has limited utility in diagnosing pathologic changes. Diagnosis is primarily based on testing of placental and fetal tissues by histopathology and molecular assays. Serological tests are mainly useful for detecting exposure, but they cannot distinguish prior infection from active reproductive disease. Improving mechanistic insight into maternal–fetal immune interactions alongside the development of reliable ante-mortem biomarkers and validated diagnostic tools is essential to better link immunopathology with clinically relevant outcomes in large animal toxoplasmosis. https://jzd.tabrizu.ac.ir/article_22032_a3cdc5ea715b1652eb528da8cab763a4.pdf