Análise TG-ROC de testes de imunofluorescência no diagnóstico de leishmaniose visceral canina

Abstract

TG-ROC analysis of immunofluorescence assays in canine visceral leishmaniasis diagnosis ABSTRACT OBJECTIVE:To analyze the accuracy of the diagnosis of two protocols of indirect immunofluorescence assays for canine visceral leishmaniasis. METHODS:Dogs from the seroepidemiological survey conducted in an endemic area of the cities of Araçatuba and Andradina, in Northwestern São Paulo state, in 2003, and in a non-endemic area of the metropolitan region of São Paulo, were used to assess two protocols of indirect immunofluorescence assay (IFA) for leishmaniasis: one using a Leishmania major heterologous antigen (IFA-BM) and another using a Leishmania chagasi homologous antigen (IFA-CH). Two-graph receiver operating characteristic (TG-ROC) analysis was used to estimate accuracy. TG-ROC analysis compared 1:20 dilution readings of the homologous antigen (IFA-CH), considered as reference test, with IFA-BM dilutions (heterologous antigen). RESULTS:The 1:20 dilution used in the IFA-CH test showed the best contingency coefficient (0.755) and the highest strength of association between the two variables studied (chi-square=124.3). Thus, it was considered the test reference dilution in comparisons with different IFA-BM test dilutions. The best IFA-BM results were obtained from 1:40 dilutions with the best contingency coefficient (0.680) and highest strength of association (chi-square=80.8). With the change in the cut-off point, recommended for the IFA-BM 1:40 dilution in this analysis, the specificity parameter value rose from 57.5% to 97.7%, even though the 1:80 dilution showed the best sensitivity estimate (80.2%), with the new cut-off point.CONCLUSIONS: TG-ROC analysis can provide important information about diagnostic tests, in addition to offering suggestions on cut-off points that can improve test sensitivity and specificity estimates and assessing these tests in terms of the best cost-benefit ratio.

Dogs with divergent serology for visceral leishmaniasis as sources of Leishmania infection for Lutzomyia longipalpis phlebotomine sand flies – an observational study in an endemic area in Brazil

“…In the present study we show that, after two years of intervention, with euthanasia of most seropositive dogs (80.2%), no change in the positivity rates of CVL could be observed. Our data are in accordance with those obtained by [33], in Rio de Janeiro (Brazil), although other studies have described a decrease in the incidence/prevalence of CVL after screening-culling procedures [11,34]. In contrast, a study in an endemic area for VL in Bahia (Brazil) showed that the removal of positive dogs was insufficient to control CVL, but reduced the strength of canine infection, with a consequent decrease in VL incidence [11].…”

“…negative results, which enable the maintenance of the transmission cycle. Low-specificity tests may result in the removal of false-positive, uninfected dogs, which discredits the controlling actions among the population, especially for those who have an affective bond with the animal [33,39]. In December 2011, the Brazilian Ministry of Health replaced the diagnosis protocol of CVL (Brazilian Ministry of Health, 2011).…”

Canine visceral leishmaniosis in an area of fishing tourism, Bonito Municipality, Mato Grosso do Sul, Central-West Brazil

“…However, some studies have reported no crossreactivity between Leishmania and other pathogens (OLIVEIRA et al, 2008;GUIMARÃES et al, 2009). Another possibility is that the levels of anti-Leishmania antibodies were below the cut-off point used as positive, as shown by SILVA et al (2009), which IFAT assay using a 1:20 dilution showed a better contingency coefficient.…”