Surveillance of Trypanosoma Cruzi Transmission by Serological Screening of Schoolchildren

Article excerpt

The seroprevalence of Trypanosoma cruzi infection among children is a sensitive indicator for assessing the effectiveness of programmes for control of Chagas disease. In this study we report the result of a cross-sectional serological survey carried out among schoolchildren living in a poor rural area in central Brazil. Eluates of blood collected on filter-paper were tested for anti-T. cruzi antibodies using immunofluorescence, haemagglutination, and enzyme-linked immunosorbent assays. The overall seroprevalence of T. cruzi infection was 7.9%, which compared with the findings of the national survey carried out in 1975-80 indicates that a twofold-to-threefold reduction in prevalence has occurred over the last 10 years. This is consistent with a reduction of transmission in the area, probably related to vector control efforts. Based on our results, the incidence of new cases was estimated to be 44 per annum in the study region. In rural areas with a scattered population, surveillance of T. cruzi transmission by serological screening of children at school entry is more practical and economical than entomological evaluation for assessing both the risk of transmission in the community and the efficacy of vector control measures. A sample size of around 1000 schoolchildren is sufficient to detect prevalences as low as 2%, and such an approach would be practical and applicable to most areas where Chagas disease is endemic.

Introduction

The WHO Expert Committee on the Control of Chagas Disease has stated that Chagas disease control is scientifically and technologically feasible[1]. The prevention of Trypanosoma cruzi infection relies on chemical control of the vector with conventional insecticide spraying, improvements in housing, and serological screening of blood donors. Chemical vector control programmes have been successfully implemented in Argentina, Brazil, and Venezuela, resulting in a significant reduction in the domestic population of vectors and interruption of transmission in large parts of these countries[2-4].

The environmental changes resulting from deforestation, mechanization of agriculture, extensive replacement of natural flora by cattle pastures, and the dislocation of rural workers to urban areas that have occurred in some areas in Brazil have also been cited as factors contributing to the control of triatomine bugs[5, 6].

In Brazil, because of political and economic constraints, as well as frequent shifts of resources to different public health problems, it has not been possible to implement regular chemical control of T. cruzi vectors in all the endemic areas. Also, the replacement of the domestic vector, Triatoma infestans, by secondary species has called attention to the importance of the peridomestic habitat in the transmission of Chagas disease and to the need for environmental management as part of the control effort.

Assessment of the impact of programmes for the control of Chagas disease is usually based on entomological monitoring of house infestation and on serological evaluation of selected cohorts of the population[7]. The seroprevalence of T. cruzi infection among children is a sensitive indicator of household rates of seropositivity, and for the assessment of the risk of transmission in the community is more practical and economical than entomological evaluation[8, 9]. In sparingly populated rural areas, where house-to-house surveys are operationally difficult, an alternative approach is the serological screening of schoolchildren[10, 11].

Here we report the result of a cross-sectional survey of schoolchildren living in a poor rural area in central Brazil, where very few economic and environmental changes have occurred in the last two decades, and where vector control activities have been kept as regular as possible. The study was designed to provide baseline information on T. cruzi transmission and to select individuals for participation in further studies on risk factors for the infection. …

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