Molecular genotyping of Babesia caballi.

Overview

• This study developed molecular tests to rapidly identify and measure different genetic types of Babesia caballi, a parasite causing equine piroplasmosis, to improve detection and prevent the spread of the disease worldwide.

Introduction to Babesia caballi and Its Significance

• Babesia caballi is a parasite that infects red blood cells in horses, causing equine piroplasmosis, a disease affecting horse health and international horse movement.
• There are three known genotypes of B. caballi, labeled A, B, and C, which differ genetically, especially in the 18S rRNA and rhoptry-associated protein (rap-1) gene sequences.
• The presence of different genotypes complicates diagnosis because some serological tests recommended by the World Organisation for Animal Health (WOAH) may fail to detect all variants, leading to false declarations of disease freedom.

Limitations of Current Diagnostic Methods

• Current serological assays may not detect all genotypes of B. caballi uniformly, especially due to genetic variation among these strains.
• A newly identified antigen, spherical body protein 4 (sbp4), holds promise as a target for serological detection, but its effectiveness across various geographical strains was previously unknown.
• Lack of molecular tools that can specifically distinguish among the three B. caballi genotypes has limited diagnostic precision.

Objective and Methodology

• The research aimed to develop molecular typing assays capable of rapid detection, differentiation, and quantification of B. caballi genotypes A, B, and C.
• Field samples were collected and screened for B. caballi presence using an established multiplex qPCR assay designed for equine piroplasmosis.
• Phylogenetic analysis was conducted on amplified sbp4 and 18S rRNA genes from South African isolates to confirm their genotype (found to be either B or C, with no genotype A detected in the samples).
• Multiple sequence alignment of sbp4 gene sequences (including published genotype A sequences) was performed to identify conserved regions suitable for primer and probe design.

Development of Genotype-specific Assays

• Three primer pairs and three genotype-specific TaqMan minor-groove binder (MGB™) probes were designed targeting the conserved regions found in sbp4.
• The molecular assays developed were qPCR-based and aimed to simultaneously detect and distinguish the three B. caballi genotypes.
• These assays demonstrated high specificity and efficiency in identifying each genotype distinctly.

Key Findings and Implications

• Genotype A was not found in the sampled field population, consistent with prior observations on regional distribution.
• The molecular phylogenetic analysis corroborated that South African field isolates belong to genotypes B or C.
• The new qPCR assays provide a robust diagnostic tool to prevent the accidental global spread of variant B. caballi genotypes by enabling accurate detection and genotyping.
• The assays can enhance biosecurity, facilitate appropriate disease management strategies, and improve surveillance programs in equine populations.

Conclusion

• This study successfully developed and validated molecular genotyping assays for B. caballi, addressing previous diagnostic limitations caused by genetic diversity.
• The application of these assays can provide more accurate detection of equine piroplasmosis infections, ensuring better disease control and international trade safety for horses.