Establishment of a model of Neospora caninum infection in pregnant mice.

The aim of this study was to establish an animal model of Neospora caninum infection in pregnant BALB/c mice infected with different doses of N. caninum tachyzoites. After infection, the female BALB/c mice were housed with male BALB/c mice. The aim of this study was to observe clinical signs and pathological changes, detect Nc5 gene expression in the main organs, and measure the wet weight and coefficient of the placenta of the pregnant mice. In addition, the level of cytokines and placental hormones in the serum was measured in pregnant mice. Our results showed that the optimal dose of the mice in the infected model was 10 tachyzoites. The infected pregnant mice presented with various clinical signs, including depression, ataxia, and variable mortality. Pathological observations of the brain, liver, and spleen in the mice exhibited hyperemia, bleeding, and swelling. Moreover, N. caninum tissue cysts or tachyzoites were observed in the brain, liver, and spleen tissues by hematoxylin-eosin (HE). The Nc5 gene was detected in the brain, liver, spleen, and placental tissues of the mice. With the increase in infection days, the weight of the placenta in the model mice increased, and the placenta ratio decreased gradually. Compared with the control group, the placenta weight and placental ratio were significantly different (P < 0.05). Furthermore, the levels of the placental hormones, corticotropin-releasing hormone (CRH), chorionic gonadotropin (CG), prolactin (PRL), and estriol (E3), and cytokines IFN-γ, IL-4, and TGF-β were differentially expressed between the model and the control group (P < 0.05 or P < 0.01), which indicated that infection with N. caninum caused an imbalance in the regulatory function of the placental hormones and cytokines in pregnant mice. A pregnant mouse model of N. caninum infection was successfully established in this study, providing a foundation for the study of the pathogenic mechanisms of N. caninum.