Biochemical and immunological indicators suggesting natural resistance to Leishmania infantum in dogs from an endemic Mediterranean area

Background Vector-borne diseases (VBDs) are the major zoonotic threats in Mediterranean regions, where dogs act as key reservoirs for pathogens such as Anaplasma phagocytophylum , Ehrlichia canis , Leishmania infantum , and Rickettsia rickettsii . Understanding how these pathogens affect the host physiology is crucial to identifying possible natural resistance against L. infantum infection and its mechanisms. This study analyzed biochemical and haematological profiles associated with single and multiple vector-borne infections in an autochthonous Sicilian dog breed naturally exposed to endemic pathogens. Methods Thirty-two clinically healthy Mannara dogs were studied in Sicily between September 2024 and January 2025. Serological detection of A. phagocytophylum , E. canis , L. infantum , and R. rickettsii antibodies was performed using IFAT, and L. infantum DNA was assessed by real-time PCR. Complete blood count, serum biochemistry, and protein electrophoresis were performed. Statistical analysis was performed using parametric or non-parametric tests, followed by false discovery rate (FDR) correction. Results None of the dogs tested were positive for L. infantum DNA, although 37.5% showed specific antibodies for this pathogen. Coinfections with two or more pathogens occurred in 40.6% of animals, mainly in adults. Dog seropositive for A. phagocytophylum showed significantly higher β2-globulin levels and lower albumin and albumin/globulin (A/G) ratios than uninfected dogs ( p -value < 0.05, FDR-adjusted). Coinfected dogs displayed elevated β2- and γ-globulin fractions and reduced albumin and A/G ratios compared with non-infected dogs ( p -value < 0.05, FDR-adjusted). Sex and age does not affect the biochemical or haematological parameters evaluated. Conclusions Mannara dogs (an autochthonous breed of the Mediterranean basin) showed biochemical evidence of chronic but balanced immune activation, despite the absence of active L. infantum infection. The decrease in A/G ratio and the increase in β2- and γ-globulins suggest sustained humoral stimulation compatible with natural resistance. Continuous exposure to multiple vector-borne pathogens may promote an immune-trained phenotype conferring resilience against L. infantum infection.