Abstract
BACKGROUND Visceral leishmaniasis is a major public health challenge in South America, and dogs are its main urban reservoir. OBJECTIVE Validation of the canine Dual-path Platform immunoassay for canine visceral leishmaniasis (DPP® CVL) for a sample set composed of 1446 dogs from different Brazilian endemic areas. METHODS A well-defined reference standard by means of parasitological culture, immunohistochemistry, and histopathology was used. Animals were classified as asymptomatic, oligosymptomatic, or symptomatic. Sensitivity and specificity were assessed as a single set and in clinical groups. A reproducibility assessment of the tests was conducted using the Kappa (κ) index at three different laboratories (A, B, and C). FINDINGS Overall, 89% sensitivity and 70% specificity were obtained for the entire sample set. Analysis of the clinical groups showed a gradual decrease in the sensitivity and an increase in the specificity with the reduction of clinical signs in the dogs that were assessed, reaching a sensitivity of 75% (42.8-94.5%) among asymptomatic dogs and lower specificity of 56% (46.2-66.3%) among symptomatic dogs. Inter-laboratory agreement was substantial (κAB= 0.778; κAC= 0.645; κCB= 0.711). MAIN CONCLUSIONS The test performance is somewhat dependent on canine symptomatology, but such influence was less evident than in previous studies. Favourable results for sensitivity and specificity can be obtained even in asymptomatic animals; however, caution is needed in these evaluations, and the results suggest that the immunochromatographic test may be further improved for better investigation in asymptomatic dogs. The results obtained confirm the usefulness of DPP® CVL for application in serological surveys.
Highlights
Visceral leishmaniasis is a major public health challenge in South America, and dogs are its main urban reservoir
The high overall sensitivity observed confirms the results of previous studies conducted with smaller sample sizes.[24,25] the DPP® CVL test was developed for joint detection of antibodies against K26 and K39 antigens,(26) and historically, studies of the anti-Leishmania canine chromatographic immunoassay formulation have indicated an increased sensitivity when using both antigens together, while the use of k39 or rk39 in isolation has resulted in lower sensitivities.[27,28] Subsequently, Otranto et al[29] reached high sensitivity with the use of the rk39 antigen alone, other studies have suggested that the combined use of different antigens is associated with increased sensitivity in immunochromatographic tests;(17,25,30) Souza Filho et al[31] demonstrated high sensitivity with the use of the AlereTM test, which utilises chimaera rK28
The parasitological methods used in this study are considered the gold standards for leishmaniasis diagnosis.[14]. Despite some limitations, such as the need for pathologist expertise in microscopic amastigote detection[33] and its susceptibility to contamination, parasitological diagnosis is still considered the best method for diagnosis because of its high specificity.[14] even considering that we used three different parasitological tests to build our reference standard, one should keep in mind that the results of the study might be slightly biased due to the well-known imperfections in the sensitivity of such tests
Summary
A well-defined reference standard by means of parasitological culture, immunohistochemistry, and histopathology was used. Combining antigens K9, K26 and K39) of L. infantum.[16] Despite such characteristics and the ease of application, discussion on the accuracy of DPP persists, especially regarding its sensitivity for detection of infected asymptomatic animals.[17] In this context, there is a need to conduct a study that addresses a representative sample of dogs from an endemic area, that uses a well-defined reference standard and blind analysis, and that follows the recommended methodological principles for the preparation and report of diagnostic accuracy studies.[18] With this perspective, this study aimed to validate and assess the inter-laboratory concordance of the DPP® CVL chromatographic immunoassay by applying it to samples of animals from different Brazilian endemic areas
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