High-Resolution Melting Analysis for Simultaneous Detection and Discrimination between Wild-Type and Vaccine Strains of Feline Calicivirus.

High-resolution melting (HRM) analysis, a post-polymerase chain reaction (PCR) application in a single closed tube, is the most straightforward method for simultaneous detection, genotyping, and mutation scanning, enabling more significant dynamic detection and sequencing-free turnaround time. This study aimed to establish a combined reverse-transcription quantitative PCR and HRM (RT-qPCR-HRM) assay for diagnosing and genotyping feline calicivirus (FCV). This developed method was validated with constructed FCV plasmids, clinical samples including nasal and oropharyngeal swabs from living cats, fresh-frozen lung tissues from necropsied cats, and four available FCV vaccines. We performed RT-qPCR to amplify a 99-base pair sequence, targeting a segment between open reading frame (ORF) 1 and ORF2. Subsequently, the HRM assay was promptly applied using Rotor-Gene Q® Software. The results significantly revealed simultaneous detection and genetic discrimination between commercially available FCV vaccine strains, wild-type Thai FCV strains, and VS-FCV strains within a single PCR reaction. There was no cross-reactivity with other common viruses in cats, including feline herpesvirus-1, feline coronavirus, feline leukemia virus, feline immunodeficiency virus, and feline morbillivirus. The detection limit of the assay was 6.18 × 10 1 copies/μl. The linear regression analysis revealed a statistically significant correlation between the C:G component percentage that presented the melting temperature shift of each strain typing pattern at 0.25 °C to 1% C:G alteration. This study, therefore, is the first demonstration of the uses and benefits of the RT-qPCR-HRM assay for FCV detection and strain differentiation in naturally infected cats.