RESUMO
To evaluate the distribution of asymptomatic infection by Leishmania infantum in a metropolis in Brazil with different relative risks (RRs) for disease and risk factors associated with the infection, an ecological study was conducted using a Bayesian approach to estimate the RR of human visceral leishmaniasis (HVL) based on cases between 2008 and 2011. The areas were categorized and selected according to disease incidence: low (area-1), medium (area-2) and high (area-3). Cross-sectional study enrolling 935 children was used to estimate the prevalence of infection by L. infantum. Volunteers from these three areas were tested for L. infantum infection by ELISA (rK39 and soluble antigens). Infection prevalence rates were estimated and compared with the RR of disease. Multilevel logistic regression model evaluated the relationship between infection and the analysed variables. The RR of HVL was distributed heterogeneously in the municipality. The infection prevalence rates were: 34·9% in area-1; 29·3% in area-2; and 33·6% in area-3, with no significant differences between these areas. The variables 'Presence of backyards in the neighbourhood' and 'Younger children' were associated with L. infantum infection. We conclude that infection by L. infantum affects a significant proportion of the infant population regardless of the RR of disease.
Assuntos
Leishmania infantum , Leishmaniose Visceral/epidemiologia , Leishmaniose Visceral/transmissão , Teorema de Bayes , Brasil/epidemiologia , Cidades , Estudos Transversais , Doenças Endêmicas/estatística & dados numéricos , Humanos , Lactente , Modelos Biológicos , Fatores de Risco , Estudos SoroepidemiológicosRESUMO
BACKGROUND: An 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. METHODOLOGY: In 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 (nâ=â317) and a number of seronegatives samples (nâ=â242) 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 FINDINGS: At 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 (nâ=â199) 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 (nâ=â82) had a mean of 56.5 parasites/mL of blood; and at follow-up the mean positive result was 7.8 parasites/mL. CONCLUSIONS: The 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.
Assuntos
Leishmania infantum/isolamento & purificação , Leishmaniose Visceral/epidemiologia , Carga Parasitária , Antígenos de Protozoários/sangue , Doenças Assintomáticas/epidemiologia , Brasil/epidemiologia , Criança , Pré-Escolar , Estudos de Coortes , Ensaio de Imunoadsorção Enzimática , Feminino , Humanos , Lactente , Leishmania infantum/genética , Leishmania infantum/imunologia , Masculino , Reação em Cadeia da Polimerase em Tempo RealRESUMO
BACKGROUND: A PCR-enzyme-linked immunosorbent assay (PCR-ELISA) was developed to overcome the need for sensitive techniques for the efficient diagnosis of Schistosoma infection in endemic settings with low parasitic burden. METHODOLOGY/PRINCIPAL FINDINGS: This system amplifies a 121-base pair tandem repeat DNA sequence, immobilizes the resultant 5' biotinylated product on streptavidin-coated strip-well microplates and uses anti-fluorescein antibodies conjugated to horseradish peroxidase to detect the hybridized fluorescein-labeled oligonucleotide probe. The detection limit of the Schistosoma PCR-ELISA system was determined to be 1.3 fg of S. mansoni genomic DNA (less than the amount found in a single cell) and estimated to be 0.15 S. mansoni eggs per gram of feces (fractions of an egg). The system showed good precision and genus specificity since the DNA target was found in seven Schistosoma DNA samples: S. mansoni, S. haematobium, S. bovis, S. intercalatum, S. japonicum, S. magrebowiei and S. rhodaini. By evaluating 206 patients living in an endemic area in Brazil, the prevalence of S. mansoni infection was determined to be 18% by examining 12 Kato-Katz slides (41.7 mg/smear, 500 mg total) of a single fecal sample from each person, while the Schistosoma PCR-ELISA identified a 30% rate of infection using 500-mg of the same fecal sample. When considering the Kato-Katz method as the reference test, artificial sensitivity and specificity rates of the PCR-ELISA system were 97.4% and 85.1%, respectively. The potential for estimating parasitic load by DNA detection in feces was assessed by comparing absorbance values and eggs per gram of feces, with a Spearman correlation coefficient of 0.700 (P<0.0001). CONCLUSIONS/SIGNIFICANCE: This study reports the development and field evaluation of a sensitive Schistosoma PCR-ELISA, a system that may serve as an alternative for diagnosing Schistosoma infection.