Low Parasite Load Estimated by qPCR in a Cohort of Children Living in Urban Area Endemic for Visceral Leishmaniasis in Brazil

Abstract

BackgroundAn important issue associated with the control of visceral leishmaniasis is the need to identify and understand the relevance of asymptomatic infection caused by Leishmania infantum. The aim of this study was to follow the course of asymptomatic L. infantum infection in children in an area of Brazil where it is endemic. The children were assessed twice during a 12-month period.MethodologyIn this population study, 1875 children, ranging from 6 months to 7 years of age, were assessed. Blood samples were collected on filter papers via finger prick and tested by ELISA (L. infantum soluble antigen and rk39). Seropositives samples (n = 317) and a number of seronegatives samples (n = 242) were subjected to qPCR. After 12 months, blood samples were collected from a subgroup of 199 children and tested for Leishmania spp. to follow the course of infection.Principal FindingsAt baseline qPCR testing identified 82 positive samples. The prevalence rate, as estimated for 1875 children based on the qPCR results, was 13.9%. The qPCR testing of whole blood samples collected from a cohort of children after 12 months (n = 199) yielded the following results: of the 44 (22.1%) children with positive qPCR results at baseline, only 10 (5.0%) remained positive, and 34 (17.1%) became negative; and of the 155 (77.9%) children with negative qPCR results, 131 (65.8%) remained negative, and 24 (12.1%) became positive at the follow-up measurement. The samples with positive findings at baseline (n = 82) had a mean of 56.5 parasites/mL of blood; and at follow-up the mean positive result was 7.8 parasites/mL.ConclusionsThe peripheral blood of asymptomatic children had a low and fluctuating quantity of Leishmania DNA and a significant decrease in parasitemia at 1-year follow-up. Quantitative PCR enables adequate monitoring of Leishmania infection.

Application of qPCR in conjunctival swab samples for the evaluation of canine leishmaniasis in borderline cases or disease relapse and correlation with clinical parameters

“…The present study assessed the diagnostic value of CS qPCR in dogs with borderline IFAT titres, suspected disease relapse or the presence of comorbidity, comparing the CS qPCR results with BC qPCR and haematochemical analyses. The use of BC samples to detect Leishmania in dogs is a much debated issue [35][36][37]. Our study confirmed that BC qPCR is not as accurate as CS qPCR as a tool to rule out suspected leishmaniasis infection.…”

Comparison of Parasitological, Serological, and Molecular Tests for Visceral Leishmaniasis in HIV-Infected Patients: A Cross-Sectional Delayed-Type Study

“…The quality parameters of the standard curves, including PCR efficiency, linear dynamic range, and correlation coefficient, were obtained by software analysis, and they were accurate and similar to the parameters obtained by previous studies from our group. 16,18 The parasite load was expressed by the Leishmania DNA load (relative copy number of the 67-bp SSU rRNA fragment) normalized against the reference gene ACTB according to the work by Overbergh and others. 19 ACTB copy numbers for the target samples were divided by the highest ACTB value obtained in the experiment, resulting in a correction factor used for normalization.…”

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…14% of 4,695 asymptomatic Ethiopians were qPCR-positive in blood of which 3.2% had high genome equivalent counts (Miller et al, 2014), suggesting that distribution of parasitaemias is skewed and that perhaps the small proportion of asymptomatic infections with higher parasitaemia are more likely to develop disease and have a disproportional role in onward transmission. However of 44 Brazilian children with positive qPCR results at baseline, only 10 remained qPCR-positive 12 months later, showing a significant decrease in genome counts (dos Santos Marques et al, 2012). Only 4 of 25 asymptomatic PCR-positive individuals remained PCR-positive 12 months later in SE Brazil (de Gouvea Viana et al, 2008).…”