Rapid identification of African swine fever virus in diagnostic samples using CRISPR-Cas

Abstract

African swine fever virus (ASFV) is a highly transmissible pathogen affecting swine, causing a devastating disease with high mortality rates in naive populations. Given the likelihood of significant economic impacts associated with an ASF outbreak, considerable resources have been allocated in the United States to safeguard the swine industry against this threat. Ongoing outbreaks of ASF in the Dominican Republic and Haiti further threaten the U.S. swine industry, given their proximity and involvement in movement to and from North America. Although surveillance programs are ongoing, limited point-of-care (POC) tests are available during outbreaks with the sensitivity and specificity standards of laboratory testing (e.g., real-time PCR [rtPCR]). However, the recently developed CRISPR-Cas–based testing systems may offer comparable high-quality results. We sought to develop a low-cost visual detection method for ASFV by employing a recombinase polymerase amplification (RPA)-dependent CRISPR-Cas12a technique that can be utilized in the field as a POC assay. Our CRISPR-Cas12a assay had comparable sensitivity and specificity to rtPCR, both visually and when quantified using a fluorescence reader. In whole blood samples from ASFV-suspect or ASFV-negative cases, our CRISPR assay achieved a sensitivity of 98.3% (10² DNA copies) and a specificity of 100%. Test results of our RPA-CRISPR assay can be visualized in as few as 7 min, with peak fluorescence at 40 min (RPA and CRISPR steps). Our results lay the groundwork for a large-scale POC assay assessment for ASFV detection and offer a robust workflow that works with commonly submitted diagnostic samples.