Bone marrow parasite load assessed by qPCR in canine leishmaniosis: Correlation and agreement with clinical status, LeishVet staging, acute phase proteins, and hematologic alterations at diagnosis.

Canine leishmaniosis causes clinical and clinicopathological abnormalities, including hematological and acute phase proteins changes. Although quantitative polymerase chain reaction (qPCR) improves diagnosis and bone marrow is one of the most sensitive samples for parasite detection, their correlation with parasite burden remains unclear. This cross-sectional study evaluated the correlation and agreement between bone marrow qPCR parasite load, clinical status, LeishVet stage, acute phase proteins, and cell blood count (CBC) alterations in dogs with leishmaniosis at diagnosis. Diagnosis was based on compatible clinical signs and/or clinicopathological findings together with positive serology and/or bone marrow qPCR for Leishmania Infantum. Dogs were excluded if they had received anti-Leishmania or immunomodulatory treatment in the previous 12 months. Published clinical score (used as surrogate of the clinical status), acute phase proteins and bone marrow qPCR parasite load scores were used, while a new CBC score based on peripheral cytopenia was developed; all scores and the LeishVet staging system were categorized into four levels. Correlation and agreement between scores were assessed using Spearman's correlation and Weighted Cohen's kappa tests, respectively. Two-hundred and seventy dogs were included into the study. The bone marrow qPCR score showed significant weak-to-moderate positive correlations with all variables and slight-to-fair agreement with all scoring systems except the CBC score. In conclusion, bone marrow qPCR parasite load in untreated dogs with canine leishmaniosis showed only weak-to-moderate associations with disease severity across the study population. However, the substantial overlap in parasite load values among clinical stages limits its usefulness for predicting disease severity in individual dogs, highlighting the need to further evaluate current staging systems for clinical management.