A comparative and evaluation of an ELISA on the Q5 recombinant protein for the diagnosis of the canine visceral leishmaniasis, incidence of false-positive results associated with the DPP test.

Abstract

Abstract Background Dogs are considered the major domestic reservoir for the human visceral leishmaniasis, a serious disease caused by the Leishmania infantum parasite. Diagnosis of the canine visceral leishmaniasis (CVL) is critical for disease control, with several methods currently available. Among the serological tests, the DPP rapid test and the EIE-LVC, more commonly used in Brazil, are associated with variable sensitivity and specificity. Research with novel recombinant proteins may therefore improve on the CVL diagnosis, such as the ELISA with the recombinant chimeric protein Q5. This study aimed to compare the Q5 in ELISA with the EIE-LVC (Leishmania major) using a large number ofCVL suspected sera (406) with a previous diagnosis based on the rapid DPP test. Methods Serum samples from dogs CVL positive in the rapid DPP test (n=406) and negative samples from healthy dogs (n=46) were used for ELISA tests using recombinant proteins Q5 and Lci13. The data obtained in the ELISA as well as the correlation with the clinical signs and the Socio-environmental characteristics of the animals were calculated using MedCalc and GraphPad Prism 8.0. Results Overall, similar levels of a lower sensitivity (67-68%) were seen for both the commercial EIE-LVC test and the Q5 ELISA when all assessed sera were considered, but a much greater sensitivity (92%) was seen for those from symptomatic dogs only. In contrast, a large number of negative results were observed for the DPP-positive sera from asymptomatic dogs or those with no clinical information available. A selection of those were tested yet again in new ELISA assays using a second batch of the Q5, purified under milder denaturing conditions, as well as another recombinant protein (Lci13). Conclusions The results reveal a higher-than-expected incidence of false-positive results for DPP, reinforcing the need for other recombinant proteins, such as the chimeric Q5, to be investigated as possible alternatives to the currently used CVL diagnostic methods.