AB Blood System Phenotypes Are Not Associated with Leishmania infantum Infection or Seropositivity in Cats from Italy

Feline leishmaniosis (FeL) caused by Leishmania infantum is increasingly recognized in endemic areas, but factors influencing susceptibility in cats remain incompletely understood. Because blood group antigens may modulate host–pathogen interactions, this study evaluated whether feline AB blood system phenotypes are associated with L. infantum seropositivity and/or molecular positivity in cats from Italy. Exploratory analyses further assessed whether blood phenotype was associated with the magnitude of indirect fluorescent antibody test (IFAT) antibody titres or with real-time PCR (qPCR) parasite load. In this retrospective cross-sectional study, cats were classified as L. infantum positive when they had an IFAT titre →1:80 and/or a positive qPCR on blood or lymph node aspirates. Feline AB blood typing was performed by tube agglutination, with type B and AB samples confirmed by immunochromatographic testing and back typing. A total of 706 cats were included. Overall, 67/706 cats (9.5%) were classified as L. infantum-positive. Blood phenotype distribution was 83.1% type A, 10.1% type B, and 6.8% type AB. L. infantum positivity was detected in all three phenotypes, and no evidence of association was found between blood phenotype and L. infantum positivity, IFAT seropositivity, qPCR positivity, IFAT titre, or qPCR parasite load. After adjustment for region, blood phenotype remained not significantly associated with L. infantum positivity. These findings suggest that feline AB blood system phenotypes were not associated with L. infantum infection in this feline cohort. Future studies should investigate whether blood phenotype may influence other aspects of FeL, such as clinical expression or disease outcome.