Serological diagnosis of canine leishmaniosis: comparison of three commercial ELISA tests (Leiscan®, ID Screen® and Leishmania 96®), a rapid test (Speed Leish K®) and an in-house IFAT

Background: Speed Leish K (R) is used as a serological screening test for Leishmania infection prior to vaccination. Limited comparative serological studies with Speed Leish K (R) have been performed. The aim of this study was to evaluate the diagnostic performance of four commercially available serologic tests including ELISAs (Leiscan (R), ID Screen (R) and Leishmania 96 (R)), a rapid test (Speed Leish K (R)) and an in-house IFAT for the detection of specific antibodies against Leishmania infantum antigen in dogs in different states of infection. Methods: Sick infected dogs (n = 36), healthy infected dogs (n = 18), L. infantum seropositive dogs with low to high levels of antibodies (n = 53), dogs seropositive to other pathogens (to evaluate cross reaction) (n = 14) and uninfected dogs from a non-endemic area (n = 50) and from an endemic area (n = 32) were analysed by the serological methods mentioned above. Results: The sensitivity was as follows: ID Screen (R) (0.953), Leiscan (R) and Leishmania 96 (R) (0.925), IFAT (0.869) and Speed Leish K (R) (0.636). The maximum specificity (1.000) was attained for all diagnostic tests except the Leishmania 96 (R) (0.896) and IFAT (0.917). The accuracy was as follows: ID Screen (R) (0.975), Leiscan (R) (0.961), Leishmania 96 (R) (0.911), IFAT (0.892) and Speed Leish K (R) (0.808). In relation to the area under the ROC curve (AUC-ROC), the maximum value was attained with the ID Screen (R) (0.993) closely followed by Leiscan (R) (0.990), then, Leishmania 96 (R) (0.962), IFAT (0.926) and Speed Leish K (R) (0.818). For the Kappa index, the best result was obtained by the ID Screen (R) (0.951) followed by Leiscan (R) (0.921), Leishmania 96 (R) (0.822), IFAT (0.783) and Speed Leish K (R) (0.622). Statistically significant differences were found between the AUC- ROC of quantitative serological tests and the only qualitative rapid test evaluated. There were also statistically significant differences between AUC-ROC of the ELISAs (ID Screen (R) and Leiscan (R)) and IFAT. Conclusions: Leiscan (R) and ID Screen (R) had superior diagnostic performance measures than IFAT and all quantitative serological tests were superior when compared to Speed Leish K (R). Thus, Speed Leish K (R) may be considered a less valuable screening test prior to vaccination as it may result in vaccination of seropositive dogs and in some cases seropositive sick dogs.