Year-round serological and molecular survey implies the spread of the re-emerged zoonotic canine Leishmania infantum from mountainous hotspot to the lowland in Beijing

Canine leishmaniasis, caused by Leishmania infantum, poses significant zoonotic risks, particularly in endemic regions. This study conducted a year-round serological and molecular survey across 16 districts in Beijing, China, from March 2021 to February 2022, aiming to investigate the prevalence and distribution of L. infantum among domestic dogs. A total of 575 canine blood samples were analyzed using enzyme-linked immunosorbent assay (ELISA) and quantitative polymerase chain reaction (qPCR), with 6.3 % testing positive (i.e., ELISA and/or qPCR positive). Infection rates varied geographically, with the highest positivity rate observed in the mountainous Mentougou District (50.0 %), suggesting a potential hotspot and source of disease spread to adjacent lowland urban areas. Risk factor analysis revealed that infection was significantly associated with age and season, with younger dogs (<6 years) and samples collected during spring showing higher positivity rates (14.1 % and 20.3 %, respectively). Gender and breed were not significant predictors. Phylogenetic analysis of ITS2 sequences confirmed the presence of L. infantum, and microscopic examination further corroborated the findings. These results underscore the importance of combined serological and molecular diagnostics for accurate detection. The observed geographical and seasonal trends suggest an urgent need for enhanced surveillance and targeted control measures to mitigate the public health risks posed by L. infantum in this rapidly urbanizing region. This study provides critical insights into the epidemiology of canine leishmaniasis in Beijing, emphasizing the role of environmental factors and reservoir hosts in disease dynamics.