Susceptibility or resistance to Bartonella spp. infection in cats: Does the phenotype-B blood matter?

Blood types can influence host susceptibility to infectious diseases by modifying erythrocyte surface antigens that act as pathogen receptors. In cats, AB blood group system polymorphisms determine the expression of distinct sialic acids, with the N-glycolylneuraminic acid (NeuGc) primarily expressed in type A, the N-acetylneuraminic acid (NeuAc) in type B, and both in type AB erythrocytes. This study investigated whether feline blood type influences susceptibility to Bartonella henselae, the agent of cat-scratch disease. A total of 454 blood and serum samples from stray colony, shelter, and owned cats in northern (Milan, Lombardy) and southern (Palermo, Sicily) was analyzed. Blood phenotyping was performed using tube agglutination, and back-typing, and immunochromatography were used to confirm type B and AB samples. B. henselae infection was determined by indirect immunofluorescence antibody test (IFAT) and real-time PCR. Univariate and multivariable logistic regression analyses evaluated associations between blood type, demographic factors, and infection markers. Overall, B. henselae infection prevalence was 19.4% (95% CI:15.8-23.3). Seropositivity was 33.3% among IFAT-tested cats, while PCR positivity was 8.8%. Geographic origin and lifestyle were strong predictors of infection: cats from southern Italy and stray colony or shelter cats were at significantly higher risk, while owned cats were protected. Blood type B was independently associated with PCR positivity (OR=2.6, 95% CI:1.1-5.6, P = 0.017). This association may reflect differences in NeuAc-mediated bacterial adhesion, but causality cannot be inferred from these data. These findings support a potential role of erythrocyte glycan composition in feline-Bartonella interactions but warrant further molecular confirmation. SIGNIFICANCE STATEMENT: This study provides preliminary evidence of an association between feline AB blood group system phenotypes and Bartonella henselae infection markers. By integrating serological and molecular diagnostics across a large, geographically diverse cat population, we observed that type B cats-characterized by NeuAc-rich erythrocyte membranes-had an approximately 2.6-fold greater probability of B. henselae DNA positivity. These findings support the hypothesis of a potential receptor-mediated mechanism underlying pathogen-erythrocyte interactions in cats, analogous to human blood group-dependent infectious processes. The work highlights how naturally occurring variation in erythrocyte glycan composition may shape host-pathogen dynamics, advancing our understanding of the evolutionary immunology of vector-borne diseases in companion animals.