Feline calicivirus (FCV) is a highly contagious virus that causes upper respiratory tract disease, commonly known as cat flu. It is widely distributed worldwide and poses a major threat to feline health. Therefore, it is essential to find an efficient and rapid method for detecting FCV. In this study, the colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay, using neutral red as an indicator, was developed and validated to target the ORF2 gene of FCV for the first time. Additionally, the study compared the diagnostic abilities of polymerase chain reaction (PCR), nested PCR, and RT-LAMP assays for detecting FCV in clinical samples. The optimized RT-LAMP amplification was carried out at 56.3 °C. The technique visually detected FCV within 70 min, with a limit of detection of 14.3 × 10¹ copies/µL, and showed no cross-reactivity with other feline pathogens. Out of 54 oropharyngeal swab samples, 17 tested positive for FCV using both nested PCR and RT-LAMP, while only one tested positive using conventional PCR. The positivity rate was higher with nested PCR and RT-LAMP (31.48%) compared to conventional PCR (1.85%). Consequently, these results demonstrated the effectiveness of the colorimetric RT-LAMP assay developed in this study as an alternative for diagnosing FCV in cats.

Feline infectious peritonitis (FIP), a devastating disease with near-complete mortality, is caused by the feline coronavirus (FCoV) and affects domestic cats worldwide. Herein, we report the development of a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay incorporating xylenol orange (XO) as a visual indicator for FCoV detection. The assay employed six oligonucleotide primers targeting regions of the nucleocapsid (N) gene. Under optimized conditions (65 °C, 60 min), amplification products were detected through pH-dependent colour changes in the XO dye. The RT-LAMP-XO assay exhibited high specificity for FCoV, with no cross-reactivity against other common feline viral pathogens. While the detection limit (1.7 × 10¹ copies/µL) was an order of magnitude higher than that of qPCR, the method offered advantages in simplicity and speed compared to existing diagnostic approaches. Although less sensitive than qPCR, the RT-LAMP-XO assay may serve as a rapid screening tool when used in combination with additional primer sets. These findings demonstrate the potential utility of XO-based RT-LAMP as a simple, visual detection method for FCoV infection.

Feline leukemia virus (FeLV) is a retrovirus that globally affects both domestic and wild cats, leading to the development of leukemia, lymphoma, and immunosuppression. However, it is important to note that the daily antigen test may yield false negative results. In this study, we successfully developed the first colorimetric loop-mediated isothermal amplification (LAMP) associated with neutral red (NR-LAMP) for the detection of FeLV. The NR-LAMP assay exhibited high sensitivity and efficiency compared to the routine polymerase chain reaction (PCR) reference method. To ensure specificity, a novel LAMP primer set was custom-designed based on the pol gene of multiple FeLV strains, which resulted in no cross-amplification with other feline viruses. Under the optimized isothermal amplification conditions at 61 °C for 40 min, the NR-LAMP assay achieved a detection limit of 10⁰ copies/µL. Using a blind clinical test involving 98 samples, the NR-LAMP assay demonstrated perfect agreement with the reference PCR method, providing a sensitivity of 97.3% and a specificity of 100%. This proposed NR-LAMP assay surpasses other related approaches in terms of sensitivity, efficiency, and cost-effectiveness. Consequently, the colorimetric NR-LAMP reaction serves as a robust and convenient diagnostic tool for the inspection of FeLV, offering an alternative molecular method for future clinical applications and commercial utilization.

Feline coronavirus (FCoV) is a major pathogen causing feline infectious peritonitis (FIP), a lethal disease in cats, necessitating accurate diagnostic methods. This study developed and compared novel primers targeting the FCoV membrane (M) gene for enhanced detection. Specific primers were designed for the M gene and their performance evaluated using reverse transcription-PCR (RT-PCR), nested RT-PCR, and reverse transcription-quantitative PCR (RT-qPCR) on 80 clinical effusion samples from cats suspected of FIP. Specificity of assays was tested against other feline viruses, with sensitivity being assessed via serial dilutions of FCoV RNA. RT-qPCR had the highest sensitivity, detecting 9.14 × 10¹ copies/µL, identifying 93.75% of positive samples, followed by nested RT-PCR (87.50%, 9.14 × 10⁴ copies/µL) and RT-PCR (61.25%, 9.14 × 10⁶ copies/µL). All assays had 100% specificity, with no cross-reactivity to other viruses. The nested RT-PCR and RT-qPCR outperformed RT-PCR significantly, with comparable diagnostic accuracy. The novel primers targeting the FCoV M gene, coupled with RT-qPCR, delivered unparalleled sensitivity and robust reliability for detecting FCoV in clinical settings. Nested RT-PCR was equally precise and amplified diagnostic confidence with its high performance. These cutting-edge assays should revolutionize FCoV detection, offering trusted tools that seamlessly integrate into veterinary practice, empowering clinicians to manage feline infectious peritonitis with unprecedented accuracy and speed.