A longitudinal study was carried out on kennelled stray dogs in a canine leishmaniasis (CanL) endemic area, to evaluate early and late diagnostic performance of a non-invasive conjunctival swab (CS) nested (n)-PCR analysis for Leishmania detection in 2 cohorts of dogs, respectively. (A) Sixty-five IFAT- and CS n-PCR-negative dogs exposed to, and followed up once or twice a month during a full sand fly season (July-November 2008). In parallel, a sand fly survey was performed on site using standard sticky traps set twice a month, for a cumulative surface of 63 m(2). (B) Seventeen IFAT- and CS n-PCR-negative dogs found positive in July 2008 at the peripheral blood buffy-coat (BC) n-PCR. These dogs were examined again by BC n-PCR in September and November 2008, and before the subsequent transmission season (May 2009) along with CS n-PCR and IFAT. None of the cohort (A) dogs converted to positive CS n-PCR during the transmission season. Although approximately 2500 phlebotomine specimens were collected with peaks of 100-147 specimens/m(2) sticky trap, the cumulative density of the only proven CanL vector in the area (Phlebotomus perniciosus) was found to be very low (0.5/m(2)). All cohort (B) dogs remained substantially seronegative; BC n-PCR showed an intermittent positive trend during the period surveyed, resulting in 82% conversions to negative by the end of the study, in contrast with 71% conversions to positive at the CS n-PCR analysis. In conclusion, while CS n-PCR was not found effective for the early detection of Leishmania contacts in dogs exposed to a low pressure of vectorial transmission, this assay showed to slowly convert to positive in a high rate of dogs, in the absence of seroconversion. CS n-PCR technique can be a suitable marker for assessing Leishmania exposure in dogs as a non-invasive alternative to current serological and molecular tools.
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