Longitudinal study of antibody kinetics and vertical transmission of Toxoplasma gondii in naturally infected pregnant sheep in Brazil.

Toxoplasmosis is a reproductive disease with a significant impact on sheep farming, particularly when it affects pregnant ewes. However, there is still a lack of data regarding the humoral immune response in naturally infected animals, as well as information on the frequency of congenital transmission. In this context, the objective of this study was to report the vertical transmission rate of Toxoplasma gondii to lambs and the kinetics of anti-T. gondii antibodies in pregnant sheep. Fifteen infected ewes (Group 1, G1) and 45 non-infected ewes (Group 2, G2) were monitored through serological tests over a six-month period. At the end of the study, 46.7% (28/60) of the sheep were seroreactive, indicating a seroconversion rate of 28.9% (13/45) in G2. Vertical transmission was observed in 38.9% (7/18) of liveborn lambs and the overall abortion rate was 10.7% (3/28). Furthermore, a significant association was detected between maternal seropositivity and the transplacental transmission of T. gondii (p = 0.024). An increase in RIPC values in the ELISA was also observed prior to abortion in three ewes; however, no statistically significant differences were identified among the sampling days (p > 0.05). These findings highlight the importance of congenital transmission as an effective route of infection in lambs, in addition to indicating fluctuations in antibody titers during the gestation of naturally infected females. In this context, understanding the maternal immune response, particularly at critical stages of pregnancy, provides valuable insights into reproductive toxoplasmosis and the failures that lead to congenital infection.