Development and validation of a recombinant Rap1-based lateral flow immunoassay for rapid serodiagnosis of bovine babesiosis in Kazakhstan.

BACKGROUND AND AIM

Bovine babesiosis, caused by , poses significant economic challenges to Kazakhstan's cattle industry. Early and accurate detection is crucial for interrupting transmission cycles, particularly in regions lacking advanced diagnostic infrastructure. This study aimed to develop a rapid lateral flow immunoassay (LFIA) using a recombinant C-terminal fragment of the recombinant rhoptry-associated protein 1 (rRap1) antigen for the serodiagnosis of bovine babesiosis.

MATERIALS AND METHODS

A C-terminal fragment (amino acids 345-480) of the gene was codon optimized and expressed in . The recombinant protein was purified using metal-affinity chromatography and validated through sodium dodecyl sulfate polyacrylamide gel electrophoresis, Western blotting, and nanoflow liquid chromatography-tandem mass spectrometry. A diagnostic evaluation was performed using enzyme-linked immunosorbent assay (ELISA) and LFIA on sera from 102 uninfected and 15 infected cattle, all of which had been pre-tested using polymerase chain reaction. Colloidal gold-protein G conjugates were prepared for LFIA, and test conditions were optimized for antigen concentration and serum dilution. Assay performance was compared with previously published LFIAs.

RESULTS

A 21-kDa rRap1 protein was successfully expressed and demonstrated high specificity to positive control sera. ELISA and LFIA both detected antibodies in 13 of 15 infected samples (sensitivity 86.6%). Specificity was 90.1% for ELISA and 88.2% for LFIA. Receiver operating characteristic analysis showed an area under the curve of 0.83, and Cohen's Kappa indicated fair-to-moderate agreement between ELISA and LFIA. The LFIA exhibited comparable performance to assays based on merozoite surface antigen 1 or spherical body protein antigens, marking the first successful use of a Rap1 C-terminal fragment for LFIA-based field diagnostics in Kazakhstan.

CONCLUSION

The developed rRap1-based LFIA is a promising, field-deployable diagnostic tool for bovine babesiosis, offering rapid results without the need for laboratory equipment. Despite slightly lower sensitivity than ELISA, its simplicity, cost-effectiveness, and specificity support its use in large-scale epidemiological surveillance. Further validation in diverse field conditions and cattle populations is recommended to refine sensitivity and broaden applicability.