Accuracy and reproducibility of a rapid chromatographic immunoassay for the diagnosis of canine visceral leishmaniasis in Brazil

Abstract

Background: Visceral leishmaniasis is a major public health concern in Brazil and the domestic dog is the main source of infection. In this study, we aimed to evaluate the accuracy and reliability of a rapid chromatographic immunoassay based on a dual-path platform for the diagnosis of canine visceral leishmaniasis (CVL).

Methods: Sampling consisted of 428 domestic dogs selected from two neighborhoods in the municipality of Fortaleza, Ceara state, Brazil. The reference standard was composed of three parasitological tests and was applied samples from 333 dogs. The rapid test was used to analyse whole blood and serum samples.

Results: Accuracy of the rapid test in whole blood samples through visual reading (n=305), serum samples through electronic reading (n=333) and serum samples through visual reading (n=333), yielded sensitivities of 87.5% (21/24; 95% CI: 66.5 to 96.7), 88% (22/25; 95% CI: 67.5 to 96.8) and 88% (22/25; 95% CI: 67.5 to 96.8), and specificities of 73.3% (206/281; 95% CI: 67.7 to 78.4), 68.2% (210/308; 95% CI: 62.2 to 74.3) and 69.2% (213/308; 95% CI: 63.7 to 74.3), respectively. Agreement between the visual and electronic readings in 428 serum samples were classified as almost perfect (Kappa Index=0.88; 95% CI: 0.83 to 0.93). The positive predictive value of the test using whole blood samples was 21.9% for the 7.9% prevalence detected by the reference standard in the study sample. A sensitivity analysis of the positive predictive value revealed that it remained below 50% in scenarios with a prevalence of up to 20%.

Conclusions: The similarity of the accuracy values of the rapid test using whole blood or serum samples, together with its reliable performance in sera through visual and electronic reading, suggests that it may contribute as a screening test for routine use under field-conditions. However, future studies need to improve the accuracy of the test so that it can be successfully implemented in public health programs.

Keywords: Diagnostic accuracy; Dogs; Leishmania infantum; Rapid tests; Serology; Visceral leishmaniasis.