Benavides, J., Katzer, F., Maley, S.W., Bartley, P.M., Cantón, G.J., Palarea Albaladejo, J., Purslow, C., Pang, Y.P., Rocchi, M.S., Chianini, F., Buxton, D.A. and Innes, E.A.
||In order to investigate the pathogenesis of neosporosis following a primary infection in late pregnancy, cattle were subcutaneously infected with 5x108 Neospora caninum (NC1 isolate) tachyzoites at day 210 of gestation and serial necropsies were then carried out at 14, 28, 42 and 56 days post-infection (dpi). No abortions occurred and all the foetuses were viable at the time of euthanasia. There was a high rate of vertical transmission, as parasite was detected by immunohistochemical labelling and PCR in all the foetuses from 28 dpi. Focal lesions, characterized as focal necrosis, were observed in the placentomes of the placenta from 28 dpi and showed resolution during later time points, denoted by infiltration of inflammatory cells at 42 dpi and fibrosis at 56 dpi. Foetuses at 28 and 42 dpi showed scarce and isolated lesions which did not represent a threat to foetal viability. No lesions were observed in the foetuses at 14 or 56 dpi suggesting control of the infection and resolution of the lesions by maternal and foetal immune responses. Although once infection was established, it could not be cleared from the host or vertical transmission of the parasite avoided. When compared to previous experimental infections at day 70 and 140 of gestation using the same challenge model, there was a delay in the arrival of the parasite to the placenta, suggesting an important change in the maternal response limiting the initial infection during the last term of pregnancy.