Hair parasite load as a new biomarker for monitoring treatment response in canine leishmaniasis

Canine leishmaniasis treatment focuses on the reduction of parasite load, the clinical improvement of the animal, and the avoidance of relapses, in a scenario where the definitive parasite clearance is not achievable. Therefore, monitoring is crucial during the treatment of this disease. Quantitative PCR has been shown as an ideal tool for the treatment monitoring when quantifying parasite load in target organs such as lymph node or bone marrow, tissues that are too invasive for regular evaluation. This study aims to prove the potential of hair parasite load in the treatment monitoring of canine leishmaniasis. Six dogs were treated with meglumine antimoniate and monitored up to four months after the end of the treatment. Parasite loads in bone marrow, blood, lymph node and hair were quantified by real-time quantitative PCR. Total IgG, IgG1, and IgG2 antibody titres were analysed by immunofluorescent assay and a clinical assessment was carried out. Treatment consisted of two 28-day courses of meglumine antimoniate (100mg/kg/day) separated by an one-month interval. Analyses were performed before (day 0), during (day 60) and after treatment (day 120), and at the end of a follow-up period (day 210, four months after the end of treatment). Hair parasite load turned out to be strongly correlated with bone marrow, lymph node and blood parasite loads and with the clinical score and the IgG1 antibody titre. The evolution of this biomarker reflects the evolution of the parasitological, immunological and clinical state of the dog, highlighting its potential as a non-invasive marker for the treatment monitoring in canine leishmaniasis.