How conjunctival swab PCR detects Leishmania in dogs outside endemic

Abstract

Due to the increasing numbers of dogs imported from or visiting Mediterranean countries, canine leishmaniasis has become an important infectious disease in countries where natural transmission typically does not occur. Although conjunctival swabs have recently been described as a useful diagnostic tool in endemic areas, their usefulness in non-endemic areas is unknown. The aim of this study was to evaluate the sensitivity and specificity of a conjunctival swab polymerase chain reaction (PCR) in dogs in a non-endemic area. Dogs (n=74) that were presented for suspected canine leishmaniasis or for screening purposes after a history of travelling were prospectively included. PCR results from conjunctival swabs were compared to those from bone marrow, lymph nodes and blood and also to antibody results determined by an indirect immunofluorescence antibody test or enzyme-linked immunosorbent assay. Dogs were considered infected if bone marrow, lymph node, or blood PCR was positive and were defined as not infected if bone marrow PCR, the gold standard of testing, was negative. The sensitivity and specificity of the conjunctival swab PCR were 78.4% (confidence interval [CI] 95%, 62.8-88.6) and 93.8% (CI 95%, 79.8-98.3), respectively. There was substantial agreement between PCR results from conjunctival swabs and lymph nodes (&#x3ba;=0.642), fair to moderate agreement between conjunctival swabs and bone marrow (&#x3ba;=0.483), and almost no agreement between conjunctival swabs and blood (&#x3ba;=0.070). Dogs with high antibody titres were more likely to be positive on conjunctival swab PCR than dogs with negative or doubtful antibody titres (P<0.001). Thus, conjunctival swab PCR is a good non-invasive test to diagnose Leishmania infection in dogs in non-endemic countries.