Hair quantitative PCR outperforms blood analysis for detecting Leishmania DNA in dogs: a non-invasive tool for clinical states of infection

BACKGROUND: Canine leishmaniosis, caused by Leishmania infantum, is a significant zoonotic disease threatening both canine and human health worldwide. Early and accurate diagnosis is crucial for effective treatment and control. The use of hair samples for molecular diagnosis of L. infantum infection in dogs is a relatively novel approach and has not yet been extensively studied. Despite recent advances in blood-based polymerase chain reaction (PCR), noninvasive alternatives like hair quantitative PCR (qPCR) remain underexplored for different clinical states of infection. This study evaluates the utility of hair samples for qPCR diagnosis compared with traditional blood-based methods in different clinical states of infection. METHODS: A total of 134 dogs from various regions of Spain, classified into healthy seronegative (n = 14), healthy seropositive (n = 59), or clinically sick (n = 61) were studied. Most sick dogs were in LeishVet stage IIa. Hair ear (n = 97) or neck (n = 37) and blood samples (n = 134) were collected. Diagnostic methods included quantitative in-house enzyme-linked immunosorbent assay (ELISA), endpoint ELISA, interferon gamma (IFN-γ) release whole blood assay, and hair and blood qPCR for Leishmania spp. RESULTS: Hair qPCR showed significantly (P < 0.001) higher sensitivity in sick dogs (74%) compared with blood qPCR (36%) while no differences were found in healthy seropositive dogs (P = 0.593). IFN-γ production was not associated with hair qPCR positivity in either healthy seropositive or sick dogs. However, medium/high ELISA seropositivity was associated with substantially increased qPCR positivity in both blood (P = 0.002) and hair (P < 0.001). Sick dogs exhibited significantly higher antibody levels (P < 0.001), while healthy seropositive dogs showed stronger IFN-γ responses (P = 0.027). CONCLUSIONS: Hair qPCR is a sensitive, non-invasive diagnostic tool for detecting Leishmania DNA in sick dogs.