Comparison of four commercial serological tests for the detection of Leishmania infantum antibodies in dogs

Early detection and treatment of cases of Leishmania infantum infection are critical in controlling the spread of the disease in dogs. Several serological methods are available to support the diagnosis of canine leishmaniosis. The immunofluorescence antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) are the main tests used by clinicians. High antibody levels are associated with severe parasitism and disease and are diagnostic of clinical leishmaniosis. Conversely, the presence of low antibody levels is not necessarily indicative of disease and may be more difficult to detect by serological tests. The aim of this study was to evaluate and compare the diagnostic performance of four commercially available serological tests, including ELISAs (CIVTEST® CANIS LEISHMANIA short and standard protocols), LEISHMANIA-ELISA DOG®, ELISA/S7® and MegaFLUO®LEISH IFAT, for the detection of specific antibodies against L. infantum antigens in dogs in different states of infection. Canine sera samples from seropositive sick infected dogs (n = 75), seropositive apparently healthy dogs (n = 48), and seronegative apparently healthy dogs from a high endemic area (Cadiz, n = 40) and seronegative apparently healthy dogs from very low endemic area of L. infantum infection (Asturias, n = 40) were classified based on the results of an in-house UAB ELISA as a reference test. The positive percent of agreement (PPA) and negative percent of agreement (NPA) observed for each test were as follows: CIVTEST® standard (93.4 %, 100 %) on 202 samples tested, CIVTEST® short (84.4 %, 100 %) on 202 samples tested, LEISHMANIA-ELISA DOG® (81.8 %, 72.2 %) on 138 samples tested, ELISA/S7® (34.8 %, 45 %) on 195 samples tested and MegaFLUO®LEISH IFAT (100 %, 100 %) on 203 samples tested, respectively. The accuracy was as follows: CIVTEST® standard (0.96), CIVTEST® short (0.91), LEISHMANIA-ELISA DOG® (0.77), ELISA/S7® (0.39), and MegaFLUO®LEISH IFAT (1). The Cohen´s Kappa index (K) from best to worst was: MegaFLUO®LEISH IFAT (K = 1), CIVTEST® standard (K = 0.92), CIVTEST® short (K=0.81), LEISHMANIA-ELISA DOG® (K =0.54), and ELISA/S7® (K=-0.19). Finally, the area under the receiver operating characteristic curve (AUC-ROC), in the ELISAs test, ordered from the maximum to the minimum value was: CIVTEST® short (1), CIVTEST® standard (0.99), LEISHMANIA-ELISA DOG® (0.87), and S7® (0.37). In conclusion, this study demonstrated that the diagnostic performance of the commercially available ELISA tests against L. infantum antigen can vary widely. Moreover, it highlights the fact that CIVTEST® CANIS LEISHMANIA is a reliable test to support the diagnosis of canine leishmaniosis in clinical settings.