Lyophilized and ready-to-use direct agglutination test in the serodiagnosis of canine visceral leishmaniasis: performance comparison.

Abstract

In the south of Europe, more than 2.5 million dogs are infected with Leishmania infantum and suffer of canine visceral leishmaniasis (CVL). More than half of these are asymptomatic and as infectious to phlebotomine sandflies as the symptomatic animals. Nowadays, there are no serological tests to apply in field conditions, sensible enough to signal these dogs. In this way, hoping to develop a sensitive, specific, easy-to-use and cheap serological tool, capable of monitor CVL and meet recommendations of World Health Organization (WHO, 2010) our group tried, in this study, to adapt a direct agglutination test (DAT) able to offer, same or better benefits, as the one already developed for the human host (Harith et al., 1995). So, we compared the performance of a DAT, where its antigen was prepared from intact Leishmania infantum promastigotes treated with β-mercaptoethanol (β-ME-DAT), with another one, conventional, tripsinated, but prepared with intact promastigotes (TRYP-DAT). The β-ME-DAT showed sensitivity and specificity values of 100% and the TRYP-DAT, respectively, 93.5% and 100%. The predictive positive value (PPV) was 93.9% in the β-ME-DAT and 87.8% in the TRYP-DAT; the predictive negative value (PPN) was respectively 100% and 97.5%. The concordance (κ=0.879, p=0.000) and correlation (0.935) obtained between the two tests with these different antigens were optimal. Despite the fact that more studies are needed to better evaluate our findings, in our opinion, this new β-ME-DAT, has the potential to detect CVL at its early stages, prior to appearance of clinical signs and parasite proliferation and consolidation. This achievement suggests new research lines directed towards early diagnosis of CVL and subsequent quick treatment, possibly using less toxic and cheaper medicines.