New epidemiological profile of schistosomiasis from an area of low prevalence in Brazil

Abstract INTRODUCTION: Schistosomiasis, caused by infection from Schistosoma mansoni, is a disease that represents an important public health problem for Brazil, especially for states in the Northeast region. Thus, the aim of this study is to present a new epidemiological profile for the disease in a municipality with low prevalence in the state of Alagoas, Brazil. METHODS: A cross-sectional study was conducted through a coproparasitological and malacological survey. A structured questionnaire was applied to the study participants to survey possible risk factors and a spatial analysis (kernel density) was used to measure the risk of infection. RESULTS: Of the 347 participants, 106 (30.5%) were infected by Schistosoma mansoni, most of them from the urban area of the municipality (68.9%; 73/106). A 3-fold risk of infection was found for individuals living in the urban area and a risk of 2.15 times for self-declared farmers. Biomphalaria glabrata and B. straminea were the species found in the municipality, but no animals were diagnosed as infected by the parasite. Spatial analysis showed a random distribution of vectors and human cases of the disease, and the formation of two clusters of human cases in the urban area was seen. CONCLUSIONS: A new epidemiological profile for schistosomiasis from S. mansoni infection was presented in a municipality of low endemicity: a high proportion of positive individuals in the urban area; presence of snails without positive diagnosis for S. mansoni infection; random distribution of vectors and human cases; and absence of association between classical risk factors and human infection.

摘要 引言：曼氏血吸虫（Schistosoma mansoni）感染引发的血吸虫病（schistosomiasis）是巴西的重大公共卫生问题，尤以东北部各州为突出。本研究旨在为巴西阿拉戈斯州一个低流行率市镇，提供该疾病的全新流行病学特征。
方法：本研究采用横断面研究（cross-sectional study）设计，通过粪便寄生虫学（coproparasitological）调查与软体动物学（malacological）调查开展研究。向研究对象发放结构化问卷（structured questionnaire）以调研潜在感染危险因素，并运用空间分析（spatial analysis）结合核密度（kernel density）法评估感染风险。
结果：共纳入347名研究对象，其中106例（30.5%）感染曼氏血吸虫，多数感染者来自该市镇城区（68.9%；73/106）。研究发现，城区居民的感染风险为非城区居民的3倍，自我申报为农民的人群感染风险为2.15倍。该市镇检出的媒介螺类为光滑双脐螺（Biomphalaria glabrata）与截形双脐螺（Biomphalaria straminea），但未检出感染该寄生虫的动物。空间分析结果显示，媒介生物与人类病例均呈随机分布，且城区存在2个人类病例聚集区。
结论：本研究报道了低流行市镇中曼氏血吸虫感染所致血吸虫病的新流行病学特征：城区感染者占比偏高；检出媒介螺类但未发现其感染曼氏血吸虫；媒介生物与人类病例分布均呈随机性；经典危险因素与人类感染无显著关联。