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

Abstract

The aim of this longitudinal study was to characterize the parasitemia of Neospora caninum and the associated immunological parameters in naturally infected beef cows for 10 months. The following groups were established: Neospora caninum seropositive pregnant cows (+Preg, n = 7), seropositive non-pregnant cows (+Npreg, n = 7), seronegative pregnant cows (-Preg, n = 4), and seronegative non-pregnant cows (-Npreg, n = 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 N. caninum DNA molecular detection and quantification. The +Preg group had a higher frequency and concentration of N. caninum DNA in PBMC in the last third of pregnancy compared to +Npreg (p <0.05), with 22 and 8% of detection, respectively. Parasitemia correlated positively with IgG titers and negatively with IgG1/IgG2 ratio (p <0.05). On day 222 of the assay, the +Preg group had the lowest total leukocyte counting (p <0.05). The +Preg group had a higher concentration of IgG and higher avidity in the last third of gestation compared to +Npreg (p <0.05). Avidity correlated with total IgG and IgG2 (p <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 N. caninum genotype from a placenta and a partial genotype from cow #3 of the group +Preg were achieved by multilocus microsatellite analysis. Overall, N. caninum 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.

Keywords: Neospora caninum; cattle; immune response; parasitemia; pathophysiology.

Figure 1

Experimental design, sample schedule, and procedures carried out.

Figure 2

The concentration of IgG, cutoff: ≥10 RIPC (A), and Avidity values (Rz) (B) of IgG from sera of Neospora caninum infected cows. Each point represents the mean ± standard error of the mean (SEM) at the different sampling times for groups +Preg and +Npreg. Correlations between Avidity (Rz) and RIPC for +Preg group (C). The significant statistical differences between groups were analyzed: *p < 0.05.

Figure 3

Optical densities (OD) of IgG1 (A), IgG2 (B), and IgG1/IgG2 ratio (C) in Neospora caninum seropositive cows. Each point represents the mean ± standard error of the mean (SEM) at the different sampling times for groups +Preg and +Npreg. Correlation between Avidity (Rz) and IgG2 (D). The significant statistical differences between groups were analyzed: *p < 0.05.

Figure 4

Mean leukocytes counting in blood from cows of four experimental groups. Total leukocytes (A) and absolute lymphocytes (B); neutrophils (C); eosinophils (D) and monocytes (E). Each point represents the mean ± standard error of mean (SEM) at the different sampling times for groups. The significant statistical differences between groups were analyzed: *p < 0.05.

Figure 5

Percentage of Neospora caninum DNA detected in PBMC using conventional PCR along gestation. Bars represent the total of positive samples/total samples analyzed and y-axis represents % of positive samples (A). Neospora caninum concentration (tachyzoites/10⁶ PBMC) along gestation. Bars represent the mean ± standard error of the mean (SEM) (B). Correlations between parasitemia and IFAT (C) and IgG1/IgG2 ratio (D). The significant statistical differences between groups were analyzed: *p < 0.05.