Abstract
Conjunctival swabs (CS) are the most promising non-invasive samples for the diagnosis and the regular screening of Leishmania infantum infection in dogs although knowledge on their diagnostic performance is still inconclusive. This study evaluates CS real time-PCR (qPCR) analysis for the diagnosis of canine leishmaniosis (CanL) and its prognostic value in seropositive dogs from an endemic area. In October 2020 (T0), 26 dogs were enrolled, divided in two groups according to anti-L. infantum antibody titres (n = 13, group low titre (LT) and n = 13, group high titre (HT)), and followed-up in August 2021. At both timepoints, animals underwent clinical examination, complete blood count and biochemical analyses, and serological (indirect fluorescent antibody test) and molecular (CS and peripheral blood qPCR) testing. At T0, 10 out of 26 enrolled dogs were positive at CS qPCR, with the number of positive animals significantly higher in group HT than in LT. After 10 months, only 5 out of 21 dogs that completed the trial still tested CS qPCR positive, and none of them developed an active CanL based on clinical score and antibody titre. None of the dogs required any leishmanicidal and/or leishmaniostatic treatments. This prospective study showed unsatisfying diagnostic and prognostic performances of CS qPCR analysis in L. infantum seropositive asymptomatic dogs from an endemic area.
Highlights
Zoonotic canine leishmaniosis (CanL) by Leishmania infantum transmitted by sand flies represents a threat for the health of dogs, the principal reservoir hosts for this protozoan [1]
The significant correlation between the severity of the disease and the level of antibody titres [6,7,8] applies to the concentration of circulating immune complexes (CICs), which have been recognized to play a pathogenic role in sick dogs [9,10,11]
In October 2020, L. infantum-seropositive dogs from a shelter located in a CanL endemic area in Apulia region, southern Italy (40.419326◦ N, 18.165582◦ E, Lecce), underwent a complete physical examination, and a clinical score ranging from 0 to 19 was assigned (Table 1)
Summary
A correct diagnostic process is crucial to identify both dogs with clinical signs compatible with L. infantum infection and asymptomatic carriers, which represent the largest infected population (up to 85%) in endemic geographical areas [2,3,4]. In veterinary practice and clinical and epidemiological studies on L. infantum, quantitative serological tests, such as indirect fluorescent antibody test (IFAT) and enzyme linked immunosorbent assays (ELISA), have been largely used due to their high diagnostic performance with a sensitivity and specificity close to 100% in dogs with clinical signs [5]. A seasonal variation in canine anti-L. infantum antibody titres has been described and should be considered in the interpretation of annual antibody screening test results and to make clinical decisions about staging, treatment, and prevention of CanL in dogs [12]
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