Canine
visceral leishmaniasis (CVL) is characterized by a high incidence of
asymptomatic infections. Because of the high prevalence of asymptomatic dogs in the endemic areas of
visceral leishmaniasis (VL), a sensitive test is required for an accurate diagnosis. In this study, we evaluated the detection of symptomatic and asymptomatic Leishmania infantum
infection in dogs using the secreted LicTXNPx
antigen (Leishmania infantum cytosolic
tryparedoxin peroxidase) in an ELISA format and compared it to soluble Leishmania
antigens from promastigote or amastigote forms (SPLA and SALA) and two other unrelated secreted Leishmania
proteins (LiTXN1 and TDR1). Moreover, we evaluated the diagnostic potential using the promastigote or amastigote-flow cytometric methodologies. The assays utilized sera collected from a cohort of L. infantum experimentally infected dogs, in which the intravenous or intradermal parasite injection mimics a symptomatic or asymptomatic pattern of
infection, respectively. Our study indicated that anti-LicTXNPx
antibodies were present in both symptomatic and asymptomatic experimental
infections. Among the different Leishmania
recombinant proteins tested, LicTXNPx showed a good predictive correlation with total soluble promastigote or amastigote Leishmania
antigens, suggesting this
antigen as a good candidate for a marker in either symptomatic or
asymptomatic infection. The use of flow cytometry using both forms of live parasites was also tested with the same group of dogs. Amastigotes were shown to have more advantages than promastigotes for the serological diagnostic in both symptomatic and asymptomatic dogs, since higher continuous levels of anti-amastigote
antibodies were detected during the course of experimental
infection. Moreover, additional studies were done using sera from non-infected dogs and clinically asymptomatic and symptomatic dogs with confirmed naturally occurring L. infantum
infections. The sensitivities of amastigote and promastigote flow cytometry were 96% vs. 89%, respectively, while the specificity for both was 93.2%. Therefore, our findings showed for the first time the potential of amastigote-flow cytometry regarding their applicability to detect both symptomatic and asymptomatic VL canine
infections.