Relationships between specific antibody responses and clinical signs of dogs living in Tunisian endemic areas of canine leishmaniasis caused by Leishmania infantum

The first step of the diagnostic process of canine leishmaniasis (CanL) is initiated by veterinarians and relies on their assessment of a high number of clinical signs common to other infectious diseases. We investigated herein the relationship between the clinical profile of 64 domestic dogs living in Tunisian endemic areas and their serological immune status with the aim to identify leishmanial serological markers of diagnosis and disease staging. Seven clinical signs were examined and a total clinical score that describes the number (TCS1) and the number plus the intensity of the clinical signs (TCS2) were determined. Laboratory tests consisted of parasitological examination (PE) of Giemsa-stained popliteal lymph node smears, indirect fluorescent antibody test (IFAT), IgG-, IgG1-, IgG2-Enzyme-Linked-Immunosorbent-Assay (ELISA), and IgG1-, IgG2- Western blotting (WB). Dogs’ categorization according to the results of routine diagnostic tests, the TCS1 and TCS2, and the relative IgG1 and IgG2 specific reactivity allowed us to show that active CanL is characterized by an increased reactivity of the IgG2 specific antibodies. Interestingly, the IgG1 levels increased in parallel with the TCS1 and especially with the TCS2, indicating that this isotype is a better marker of dogs’ health deterioration. PE & IFAT positive dogs which presented the highest TCS2 and IgG1 reactivity demonstrated significantly more severe weight loss and paleness of the mucosal membranes, suggesting that these signs characterize the latest stages of the disease. WB analysis showed that threeleishmanial polypeptides merit attention and further investigations. The antigens with MWs 32kDa reacting with IgG1 and 37kDa reacting withIgG2 antibodies were found associated with the results of diagnostic tests and late CanL stages, whereas the 24kDa antigen reacting with the IgG2 isotype and associated with low TCS2 seems to be a marker of the early stages.