Parasitemia and Associated Immune Response in Pregnant and Non-Pregnant Beef Cows Naturally Infected With .

The aim of this longitudinal study was to characterize the parasitemia of and the associated immunological parameters in naturally infected beef cows for 10 months. The following groups were established: seropositive pregnant cows (+Preg, = 7), seropositive non-pregnant cows (+Npreg, = 7), seronegative pregnant cows (-Preg, = 4), and seronegative non-pregnant cows (-Npreg, = 4). Several samples were obtained for absolute and relative leukocyte counting, cytokines IL-10, IL-12, α-TNF, and γ-IFN quantification, specific IgG, IgG1, and IgG2 and avidity and DNA molecular detection and quantification. The +Preg group had a higher frequency and concentration of DNA in PBMC in the last third of pregnancy compared to +Npreg ( <0.05), with 22 and 8% of detection, respectively. Parasitemia correlated positively with IgG titers and negatively with IgG1/IgG2 ratio ( <0.05). On day 222 of the assay, the +Preg group had the lowest total leukocyte counting ( <0.05). The +Preg group had a higher concentration of IgG and higher avidity in the last third of gestation compared to +Npreg ( <0.05). Avidity correlated with total IgG and IgG2 ( <0.05). All +Preg cows gave birth to clinically healthy but seropositive calves before colostrum intake, therefore, the congenital transmission was 100% efficient. Only a complete genotype from a placenta and a partial genotype from cow #3 of the group +Preg were achieved by multilocus microsatellite analysis. Overall, parasitemia is frequent in seropositive beef cows during the last third of gestation. This correlates with higher antibody levels and a decrease in total leukocyte counting. The precise timing of the parasitemia may be used for diagnosis purposes and/or for design strategies to avoid vertical transmission. Further studies are needed to identify the immune molecular mechanisms that favor parasitemia during gestation in chronically infected cattle.