Development of a rapid and highly accurate diagnostic test for detecting Theileria equi in horses using recombinase polymerase amplification (RPA) combined with nucleic acid lateral flow immunoassay.

Overview

• This study developed a rapid, highly accurate diagnostic test for detecting Theileria equi, the protozoan causing equine piroplasmosis in horses.
• The test uses recombinase polymerase amplification (RPA) combined with a nucleic acid lateral flow immunoassay (LFD) to provide results within 25 minutes without specialized equipment.

Background

• Equine piroplasmosis (EP) is a disease caused primarily by Theileria equi, affecting horses and causing symptoms like fever, anemia, and edema.
• The disease’s non-specific clinical signs make it difficult to diagnose based on symptoms alone.
• A significant challenge is the presence of many carrier horses that show no overt signs but harbor the pathogen.
• Current diagnostic methods include molecular, serological, and microscopic techniques, but these require specialized tools, trained personnel, and are time-consuming.

Objective

• To develop a rapid, sensitive, and specific diagnostic assay capable of detecting Theileria equi in horses.
• To simplify diagnostics by creating a method that does not rely on complex lab equipment or prolonged testing times.

Methodology

• The study used recombinase polymerase amplification (RPA), an isothermal DNA amplification technique that works rapidly at a constant temperature, suitable for field use.
• Pre-labeled DNA primers were utilized to facilitate detection after amplification.
• The amplification products were detected using a nucleic acid lateral flow immunoassay (LFD), a paper-based strip test similar to pregnancy tests, allowing easy visualization of results.
• Sample evaluation included 30 clinical samples tested for Theileria equi presence.

Results

• Out of 30 samples tested, 23 were identified as positive for Theileria equi using the new assay.
• No false positives were detected, indicating 100% specificity.
• The detection limit was as low as 5 ng per microliter of DNA, showing high sensitivity.
• The total time from sample preparation to result interpretation was approximately 25 minutes.
• The assay did not require any specialized or sophisticated equipment, highlighting its potential for use in field conditions.

Significance and Implications

• This RPA-LFD assay provides a fast, easy-to-use, and accurate diagnostic tool for detecting Theileria equi, potentially improving disease management and control.
• Its specificity and sensitivity match or exceed conventional methods but are much quicker and simpler.
• The rapid turnaround time and minimal equipment requirements make it suitable for on-site testing, enabling timely decision-making in equine health management.
• This approach could decrease the reliance on centralized labs and reduce costs associated with EP diagnosis.

Limitations and Future Directions

• Currently, the assay requires DNA extraction prior to testing, which involves some technical skill and processing time.
• Further research is needed to optimize the assay to directly detect Theileria equi from samples without the DNA extraction step.
• Validation with a larger number of field samples and diverse geographic locations would strengthen confidence in the assay’s broad applicability.
• Exploration into integrating sample preparation with the assay for a fully automated or point-of-care diagnostic device could be pursued.