Theileria annulata antibody level to clinical surveillance of disease progression and parasite stage differentiation in bovine host.

Understanding the progression of Theileria annulata infection is essential for effective treatment and control of theileriosis transmission. A PCR method was used to detect the parasite's sporozoite surface protein gene (TaSP), and the results were compared with two quantitative indirect ELISAs targeting stage-specific antibodies. The early-stage ELISA focused on sporozoite-stage antibodies, while the late-stage ELISA targeted merozoite-stage antibodies based on the TaSP linear B cell peptide epitope and rTaMS protein, respectively, to identify life stages (sporozoite and merozoite) and disease phases (acute, chronic, and recovered) in infected animals. The agreement analysis of PCR with late-stage ELISA showed no agreement (κ = -0.062) and high discordance (χ2 = 30.77), whereas PCR with early-stage ELISA exhibited significant concordance (κ = 0.17) and lower discordance (χ2 = 6.63). The correlation between early and late-stage ELISA is statistically significant (r = 0.6054). In this study, we quantitatively measured antibody levels against two parasitic stages (sporozoite and merozoite) in individual samples for clinical surveillance of disease progression in bovine. Out of 229 field samples, the majority (22.7%) indicated active ongoing infection, 19.2% suggested very recent infection, 16.2% indicated acute or early-stage infection, 10.5% were unexplored or healthy, and 9.6% showed signs of recovered chronic infection. This is the first experimental study to quantitatively monitor individual samples for antibody levels against two parasite stages, alongside PCR, to track stage-specific disease progression. Combining PCR with quantitative indirect early and late-stage ELISA offers an effective approach to differentiate among ongoing active, recovered, acute, and chronic phases of infection.