Diagnostic performance of parasitological, immunological and molecular tests for the diagnosis of Schistosoma mansoni infection in a community of low transmission in Venezuela.

In Venezuela, areas endemic for schistosomiasis are of low transmission, with low parasite loads. Immunological tests often lack specificity and cannot differentiate past from present infections. Molecular tests are an alternative, although validation studies in endemic areas are needed. The aim of this study was to determine the performance of parasitological, immunological and molecular tests for the diagnosis of Schistosoma mansoni infection in low-transmission settings. A cross-sectional study was carried out in a rural community located in a schistosomiasis-endemic area of Venezuela to determine the prevalence and diagnostic performance of the Kato-Katz (KK) technique, Circumoval Precipitin Test (COPT), ELISA based on soluble egg antigen (ELISA-SEA) with and without treatment with sodium metaperiodate (ELISA-SEA-SMP), and PCR for amplification of the 121 bp highly repeated sequence of Schistosoma mansoni in faeces, urine and serum samples. The highest prevalence rates were obtained with ELISA-SEA (38.7%), COPT (33.3%), ELISA-SEA-SMP (31.5%), PCR on faeces (21.6%), and KK (17.1%), whereas PCR-based prevalence in urine was 6.2% and no positivity was detected in serum samples. Results showed that ELISA-SEA is the best method for the diagnosis of both current and former infections and that PCR on faeces is the best method for detecting recent transmission. The use of different tests that complement one another also allowed for a better diagnosis of Schistosoma mansoni infection, revealing a relatively high prevalence (33.8%) of schistosomiasis in a community of low transmission.

Evaluation of parasitological and molecular techniques for the diagnosis and assessment of cure of schistosomiasis mansoni in a low transmission area

This study evaluated parasitological and molecular techniques for the diagnosis and assessment of cure of schistosomiasis mansoni. A population-based study was performed in 201 inhabitants from a low transmission locality named Pedra Preta, municipality of Montes Claros, state of Minas Gerais, Brazil. Four stool samples were analysed using two techniques, the Kato-Katz® (KK) technique (18 slides) and the TF-Test®, to establish the infection rate. The positivity rate of 18 KK slides of four stool samples was 28.9% (58/201) and the combined parasitological techniques (KK+TF-Test®) produced a 35.8% positivity rate (72/201). Furthermore, a polymerase chain reaction (PCR)-ELISA assay produced a positivity rate of 23.4% (47/201) using the first sample. All 72 patients with positive parasitological exams were treated with a single dose of Praziquantel® and these patients were followed-up 30, 90 and 180 days after treatment to establish the cure rate. Cure rates obtained by the analysis of 12 KK slides were 100%, 100% and 98.4% at 30, 90 and 180 days after treatment, respectively. PCR-ELISA revealed cure rates of 98.5%, 95.5% and 96.5%, respectively. The diagnostic and assessment of cure for schistosomiasis may require an increased number of KK slides or a test with higher sensitivity, such as PCR-ELISA, in situations of very low parasite load, such as after therapeutic interventions.

Neglected tropical diseases: prevalence and risk factors for schistosomiasis and soil-transmitted helminthiasis in a region of Minas Gerais State, Brazil.

BACKGROUND: Among the neglected tropical diseases (NTDs), schistosomiasis and the three main soil-transmitted helminthiases (STHs), i.e., ascariasis, trichuriasis and hookworm infection, represent the most common infections in developing countries. In Brazil, there is a lack of epidemiological data in many parts of the country, which favors the unawareness of the real situation concerning these diseases. Due to this, we investigated the occurrence of schistosomiasis and STHs in a region of Minas Gerais State, Brazil. METHODS: One stool sample was collected from 503 individuals, whose ages ranged from 0.1 to 91.2 years, and screened using both the Kato-Katz and the Formol-Ether methods. In parallel, a malacological survey was carried out in the main water bodies of the district, and Biomphalaria susceptibility assays and kernel-based techniques were also performed. RESULTS: No individual was found infected with Ascaris lumbricoides or hookworm. Schistosoma mansoni was the most common parasite found (1.6%). The prevalence was higher in males and the chance of acquiring the disease increased by 43.35 times with contact with a body of water. None of the Biomphalaria tenagophila and B. glabrata specimens were found naturally infected, but B. glabrata was highly susceptible to infection with Schistosoma mansoni. Using kernel-based techniques, clusters of Biomphalaria were found near the households where the infected individuals lived. CONCLUSIONS: Schistosomiasis was the most prevalent parasitic infection found. Our findings show that the occurrence of this disease has been underestimated by the local health care service, and highlight the importance of epidemiological surveillance in areas of low prevalence for schistosomiasis.

Evaluation of two coproscopic techniques for the diagnosis of schistosomiasis in a low-transmission area in the state of Minas Gerais, Brazil

This population study, which evaluated two parasitological methods for the diagnosis of schistosomiasis mansoni, was performed in a low-transmission area in Pedra Preta, Montes Claros, Minas Gerais, Brazil. A total of 201 inhabitants of the rural area participated in this research. Four stool samples were obtained from all participants and analysed using the Kato-Katz method (18 slides) and a commercial test, the TF-Test®, which was performed quantitatively. The data were analysed to determine prevalence, the sensitivity of the diagnostic methods, the worm burden and the definition of the "gold standard", which was obtained by totalling the results of all samples examined using the Kato-Katz technique and the TF-Test®. The results showed that the prevalence obtained from the examination of one Kato-Katz slide (the methodology adopted by the Brazilian control programme) was 8 percent compared to 35.8 percent from the "gold standard", which was a 4.5-fold difference. This result indicates that the prevalence of schistosomiasis in so-called low-transmission areas is significantly underestimated.

Clinical and ultrasound findings before and after praziquantel treatment among Venezuelan schistosomiasis patients

Abdominal ultrasound can be a useful tool for diagnosing periportal fibrosis related to Schistosoma mansoni infection, and also for planning and monitoring the evolution of hepatic morbidity following control measures. We evaluated the standardized ultrasound methodology proposed by the World Health Organization for detecting periportal fibrosis and portal hypertension, among patients from an endemic area in Venezuela, and the impact of praziquantel treatment 3-5 years later. After chemotherapy, complete reversal of periportal lesions was observed in 28.2 percent of the cases and progression of the disease in 5.1 percent. Improvement in the hepatic disease started with a reduction in the periportal thickening followed by a decrease in the size of the left hepatic lobe, spleen and mesenteric and spleen veins. Ultrasound confirmed the clinical findings after chemotherapy among the patients with reversal of the disease. However, in patients with more advanced disease, these findings were contradictory. There was no correlation between evolution of the disease seen on ultrasound and age, intensity of infection or serological findings.

O ultra-som abdominal pode ser uma ferramenta útil para o diagnóstico da fibrose periportal relacionada à infecção por Schistosoma mansoni, e também para planejar e monitorar a evolução da morbidade hepática após medidas de controle. Nós avaliamos a metodologia padronizada no ultra-som, proposta pela Organização Mundial da Saúde, para a detecção da fibrose periportal e hipertensão porta, em pacientes de área endêmica da Venezuela e o impacto do tratamento com praziquantel 3-5 anos depois. Após quimioterapia, houve reversão completa das lesões periportais em 28,2 por cento dos casos e progressão da patologia em 5,1 por cento. A melhora da patologia hepática começou com a redução do espessamento periportal seguida pela diminuição do tamanho do lobo esquerdo, baço e veias mesentérica e esplênica. O ultra-som confirma os achados clínicos após quimioterapia em pacientes com reversão da patologia; contudo, naqueles com patologia mais avançada, estes achados foram contraditórios. Não houve correlação entre evolução da patologia ultra-sonográfica com idade, intensidade da infecção ou achados sorológicos.