Development and Validation of a New Scoring System (Total Leishmania Score) for Dogs with Leishmania infantum Infection Including Clinical and Laboratory Parameters

Canine leishmaniosis can cause a variety of signs. The detailed assessment of disease severity lacks a standardized, validated scoring system. This prospective study aimed to develop and validate an objective scoring system (“Total Leishmania Score”, TLS) combining clinical and laboratory parameters for monitoring dogs with Leishmania (L.) infantum infection. Fifty-one L. infantum-infected dogs were examined every 3 months over 1 year. Evaluations included physical examination, complete blood count, serum biochemistry, urinalysis including protein-to-creatinine ratio, and a L. infantum antibody Enzyme-Linked Immunosorbent Assay (ELISA). At each visit, 2 veterinarians applied the TLS, comprising 10 clinical and 8 laboratory parameters graded on a four-point severity scale (0–3) and weighted according to their estimated prognostic relevance values. Interobserver agreement was assessed using intraclass correlation coefficients (ICCs) and Bland–Altman analysis. Longitudinal changes were analyzed using robust linear mixed-effects models. In total, 488 scores were evaluated. Interobserver reliability was excellent (ICC: 0.998; CI95%: 0.997–0.998; p < 0.001) with no relevant systematic bias. Reliability remained excellent at all time points (ICC: 0.996–0.999). The TLS increased significantly before and during relapse (p < 0.001) and decreased significantly within 3 months after leishmanicidal treatment (p < 0.001). The TLS demonstrated excellent reliability and responsiveness, supporting its use for the longitudinal monitoring of dogs with leishmaniosis.