Abstract
Background and Aim: Feline leukemia virus (FeLV) infection remains an important cause of morbidity and mortality in domestic cats. Conventional p27 antigen assays are widely used for screening but may fail to detect proviral DNA in cats without detectable antigenemia. This study aimed to evaluate a polymerase chain reaction (PCR) assay targeting the conserved FeLV pol gene for molecular detection of FeLV and to compare its diagnostic performance with a commercial p27 antigen rapid immunoassay in an enriched clinical cohort of Thai cats.
Materials and Methods: A total of 160 residual ethylenediaminetetraacetic acid-blood specimens were obtained from an enriched referral cohort of cats presented to Kasetsart University Veterinary Teaching Hospital for FeLV screening or blood-donor qualification. Proviral DNA was analyzed by conventional PCR targeting an approximately 791-bp fragment of the FeLV pol gene, and results were compared with those of the commercial p27 antigen assay. PCR products from discordant specimens were subjected to Sanger sequencing and sequence comparison with reference FeLV pol sequences. Diagnostic sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy were determined.
Results: FeLV proviral DNA was detected by pol gene PCR in 137/160 (85.6%) specimens, whereas 94/160 (58.8%) were positive by the p27 antigen assay. All 94 antigen-positive specimens were PCR-positive, while 43/160 (26.9%) were PCR-positive but antigen-negative. Using PCR as the reference standard, the antigen assay showed 68.61% sensitivity (95% confidence interval: 60.13–76.27%), 100% specificity, 100% PPV, 34.8% NPV, and 73.13% overall accuracy. Sanger sequencing of discordant PCR-positive/antigen-negative specimens demonstrated 98% nucleotide identity with reference FeLV pol sequences, supporting the presence of FeLV proviral DNA in these antigen-negative specimens.
Conclusion: The pol gene PCR detected substantially more FeLV-positive specimens than p27 antigen testing in this enriched clinical cohort, particularly among antigen-negative cats harboring detectable proviral DNA. Incorporating molecular testing as a complementary method may improve detection in high-risk cats, blood-donor screening, and cases with discordant or clinically suspected FeLV infection. Because the cohort was deliberately enriched, the observed positivity rates should not be extrapolated to the general Thai cat population.
Keywords: antigen detection, diagnostic accuracy, feline leukemia virus, latent infection, molecular diagnosis, polymerase chain reaction, proviral DNA, Thailand.