Assessment of circulating immune complexes in canine leishmaniosis and dirofilariosis

Canine leishmaniosis (CanL) by Leishmania infantum (L.i.) and heartworm disease by Dirofilaria immitis (D.i.) are common zoonotic vector-borne diseases (VBDs) characterized by a variety of pathological and clinical signs. The immunopathology in both VBDs is extremely complex, and their clinical manifestations are strongly dependent on the type of immune response elicited by the parasites. In particular, the formation of circulating immune complexes (CICs) plays an important role in the pathogenesis of these VBDs. Based on the international guidelines, dogs with high anti-L. infantum antibody titres and one or more clinical and/or laboratory signs related to CanL require anti-Leishmania treatment. Consequently, the CICs measurement could be used for improving the clinical staging process of CanL. The aim of the study was to assess the CICs level by a competitive inhibition enzyme immunoassay, in healthy or sick dogs seropositive to L.i. and in healthy dogs positive to D.i. Out of 51 enrolled dogs, 11 were included in Group A (seronegative to L.i., D.i. negative and healthy), 15 in Group B (exposed to L.i., D.i. negative and healthy), 12 in Group C (seropositive to L.i., D.i. negative and sick) and 13 in Group D (seronegative to L.i, D.i. positive and healthy). The comparison of CIC level in canine sera revealed a significant difference among groups (P < 0.001), with the highest concentration (i.e., median = 104.6 µg/mL) in dogs with CanL. The findings of the study highlight the CICs measurement as a useful tool in the clinical staging of CanL for avoiding misclassification of dogs as leishmaniotic, thus not requiring anti-Leishmania therapy, as well as the possibility of results misuse in geographical areas where both leishmaniosis and heart-worm disease are endemic.