An Extraction-free One-Pot Assay for Rapid Field Discrimination of African Swine Fever Virus Variants by a Single-Step RPA-CRISPR/Cas12a Strategy.

Abstract

African swine fever virus (ASFV) causes devastating outbreaks in swine populations worldwide. The co-existence of wild-type and emerging gene-deleted variants (e.g., ASFV-ΔI177L) necessitates rapid on-site diagnostic tools for strain identification, which is critical for timely disease control and tailored farm management. Here, we developed a field-deployable, extraction-free one-pot assay (CORDSv2) that combines multiplex RPA and CRISPR/Cas12a to target conserved ASFV sequences and specific fluorescent markers (eGFP/mCherry) of gene-deleted variants. The assay achieved ultrasensitive detection (LOD: 6 copies/μL) and demonstrated 97.9% accuracy with 96 field samples. To streamline field operations, we integrated an extraction-free protocol (for serum/saliva) with freeze-dried reagent microspheres, enabling stable storage and direct use with minimal manual handling. When paired with a portable fluorometer (hippoCORDS), the system completes the entire sample-to-answer workflow within 1 h with a single step: addition of lysate to the microspheres. This robust, portable system addresses the urgent need for simple, on-site ASFV variant surveillance and is adaptable for other high-threat pathogens.