Association between allergic responses and Schistosoma mansoni infection in residents in a low-endemic setting in Brazil

Introduction Schistosomiasis is endemic in 76 countries and territories. Several studies have found an inverse correlation between parasitic disease and the development of allergies. The purpose of the present study was to determine whether infection with Schistosoma mansoni in subjects with a low parasite load is protective against allergy. The final sample consisted of 39 S. mansoni-positive and 52 S. mansoni-negative residents of a small community in northeastern Brazil. Methods All subjects were submitted to the Kato-Katz test, anti-S. mansoni IgG measurement, the prick test for aeroallergens, eosinophil counts and serum IgE measurement. Results Subjects who reacted to one or more antigens in the prick test were considered allergic. Only 7 S. mansoni-positive subjects (17.9%) reacted to one or more antigens, whereas 20 S. mansoni-negative subjects (38.5%) tested positive for allergy. Conclusions Our findings suggest that, in areas of low endemicity, infection with S. mansoni significantly reduces the risk of the development of allergy in subjects with a low parasite load. .

A conventional polymerase chain reaction-based method for the diagnosis of human schistosomiasis in stool samples from individuals in a low-endemicity area

The aim of this study was to evaluate the efficacy of a polymerase chain reaction (PCR)-based method to detect Schistosoma mansoni DNA in stool samples from individuals living in a low-endemicity area in Brazil. Of the 125 initial stool samples, 80 were ELISA reactive and eggs were identified in 19 of the samples by parasitological examination. For the PCR evaluations, 56 stool samples were selected and divided into five groups. Groups I-IV were scored negative for S. mansoni eggs by parasitological examination. Groups I and II were ELISA reactive, whereas Groups III and IV were ELISA nonreactive. Groups II and III were positive for other intestinal parasites. PCR testing scored eight samples as positive from these four groups. Group V represented the S. mansoni -positive group and it included ELISA-reactive samples that were scored positive for S. mansoni by one or more parasitological examinations (6/19 were positive by Kato-Katz method, 9/17 by saline gradient and 10/13 by Helmintex®). PCR scored 13 of these 19 samples as positive for S. mansoni . We conclude that while none of these methods yielded 100% sensitivity, a combination of techniques should be effective for improving the detection of S. mansoni infection in low-endemicity areas.

The combination of three faecal parasitological methods to improve the diagnosis of schistosomiasis mansoni in a low endemic setting in the state of Ceará, Brazil

Laboratory diagnosis of intestinal schistosomiasis mansoni can be accomplished through various methods of stool examination to detect parasites, ranging from the most classic tests (Kato-Katz) to several methods that are still undergoing validation. This study was conducted to assess two new parasite identification methods for diagnosing schistosomiasis mansoni in residents of a low endemic area in the municipality of Maranguape, in the state of Ceará, Brazil using the Kato-Katz method as a reference and serology (enzyme-linked immunosorbent assay) for the screening of patients. The Kato-Katz, the saline gradient method and the Helmintex® method parasite identification methods were employed only in subjects who exhibited positive serologic tests. The test results were then analysed and treatment of positive individuals was subsequently performed. After comparing the test results, we observed that the saline gradient method and the Helmintex® method were more effective in diagnosing schistosomiasis mansoni in the study area compared with the Kato-Katz method.

Increased detection of schistosomiasis with Kato-Katz and SWAP-IgG-ELISA in a Northeastern Brazil low-intensity transmission area / Aumento da detecção da esquistossomose com Kato-Katz e SWAP-IgG-ELISA, em área de baixa endemicidade, no nordeste do Brasil

INTRODUCTION: The laboratory diagnosis of schistosomiasis is based mainly on the detection of parasite eggs in stool samples through the Kato-Katz (KK) technique, reading one slide by test. However, a widely known limitation of parasitological methods is reduced sensitivity, particularly in low endemic areas. METHODS: To increase sensitivity, we conducted further slide readings from the same stool sample using the parasitological method associated with a serological test. We used the KK method (three slides) and the IgG anti-Schistosoma mansoni-enzyme-linked immunosorbent assay (ELISA) technique to diagnose schistosomiasis in low endemic areas in the Brazilian State of Ceará. Fecal samples and sera from 250 individuals were analyzed. RESULTS: Sixteen percent and 47.2% of samples were positive in parasitological tests and serological tests, respectively. Parasitological methods showed that 32 (80%) individuals tested positive on the first slide, 6 (15%) on the second slide, and 2 (5%) on the third. The performance of the ELISA test in the diagnosis, using the KK method as diagnostic reference, showed a negative predictive value of 100%, with specificity and positive predictive values of 62.8% and 33.9%, respectively. CONCLUSIONS: In this study, the increase from one to three slides analyzed per sample using the KK technique was shown to be a useful procedure for increasing the diagnostic sensitivity of this technique.

INTRODUÇÃO: O diagnóstico laboratorial da esquistossomose é baseada principalmente na detecção de ovos do parasito nas fezes, realizada pela técnica de Kato-Katz (KK), com a leitura de uma lâmina por teste. No entanto, uma limitação conhecida dos métodos coproscópicos é a reduzida sensibilidade, especialmente nas áreas de baixa endemicidade. MÉTODOS: A fim de reduzir essa limitação, realizamos mais leituras da mesma amostra de fezes pelo método coproscópico e associamos a um teste sorológico.Utilizamos o método de KK (três lâminas) e a técnica de IgG-ELISA, buscando aumentar a sensibilidade do diagnóstico da esquistossomose em área de baixa endemicidade, no Estado Brasileiro do Ceará. Amostras de fezes e soro de 250 indivíduos foram analisadas. RESULTADOS: Destas, 40 e 118 foram positivas nos testes coproscópico e sorológico, respectivamente. Na coproscopia, 32 (80%) indivíduos tiveram testes positivos na primeira lâmina, 6 (15%) na segunda e 2 (5%) apenas na terceira lâmina. O desempenho do teste de ELISA no diagnóstico utilizando-se o método KK como referência de diagnóstico, demonstrou valor preditivo negativo de 100% mas a especificidade e o valor preditivo positivo foram de 62,8% e 33,9%, respectivamente. CONCLUSÕES: Neste estudo, o aumento de uma para três lâminas analisadas por amostra pelo KK, mostrou ser um procedimento útil para o aumento da sensibilidade diagnóstica desta técnica.