Mixed infection of FeLV-A and FeLV-B caused more severe anemia and death in infected cats

Feline leukemia virus (FeLV) exhibits remarkable subtype diversity and is associated with fatal outcomes including anemia and lymphoma. However, there is a virtual void of FeLV-related research in China. In this study, 536 samples were detected using the qPCR method, followed by the amplification of the env gene sequences for genetic evolution and recombination analyses. Our results demonstrated a 2.2% positivity rate (12/536), with successful env gene amplification from four FeLV-A and FeLV-B positive samples. Phylogenetic reconstruction revealed that Chinese FeLV-A strains likely originated from multiple countries. Importantly, recombination analysis confirmed FeLV-B emergence through genetic recombination between FeLV-A and enFeLV. Electron microscopy visualized characteristic FeLV particles, while necropsy and histopathological examination identified lymphoma-like lesions. In conclusion, these findings reveal that FeLV-A strains pose a risk of transmission in China. They can recombine with enFeLV to generate FeLV-B with enhanced pathogenicity, leading to severe anemia in infected cats and accelerating their death process.