Schistosoma mansoni in Lake Tana: A comprehensive assessment of parasite, snail vector, and associated factors at Gorgora, Northwest Ethiopia

Abstract

Background: Schistosomiasis is one of the neglected tropical diseases of public health importance worldwide. The transmission of this disease is linked to freshwater snails. It has been reported from 78 countries and territories, affecting approximately 290.8 million individuals who required treatment in 2018. The burden of this disease continues to be significant in specific regions, especially in sub-Saharan Africa, despite more than two decades of mass preventive chemotherapy primarily targeting school-aged children. In Ethiopia, the prevalence of the disease in children ranges from 24 to 90% in different localities. While previous studies have primarily concentrated on disease prevalence, there is a lack of attention to the distribution of snails and their infectivity status. This study sought to evaluate the distribution of snails and identify factors related to Schistosoma mansoni infection along Lake Tana at Gorgora, Northwest Ethiopia.

Methods: A community-based cross-sectional study was conducted along Lake Tana in Gorgora town, Northwest Ethiopia from March to May 2020. A total of 385 study participants were selected by systematic random sampling technique. Kato-Katz smears were prepared from stool sample and examined microscopically to confirm S. mansoni eggs. A malacological survey was conducted at 14 sites along Lake Tana shore. Collected snails were put in a small plastic bucket that contained water and plant vegetation, and transported to vector biology laboratory, University of Gondar, within four hours of collection for morphological identification and Cercaria shedding. Data were entered into EpiData version 4.4.2.1 and transferred to SPSS version 20.0 and STATA version 15.0 for analysis. Spatial distribution analysis was done using the ArcGIS system. A P value ≤ 0.05 was considered as statistically significant.

Result: The prevalence of S. mansoni was 36.6% (95% CI: 32.0-41.9). The infection intensity category of Schistosoma mansoni was light (30.5%), moderate (42.5%), and heavy (27.0%). From a total of 1105 snails collected, 546 (49.4%) were Biomphalaria species, 310 (28.1%) were Bulinus species, 105(9.5%) were Lymnae species, and 144(13.0%) were Bivalve. None of the Biomphalaria species collected were infected with human schistosoma. Lake water practice, swimming frequency, and proximity to the lake were significantly associated factors of Schistosoma mansoni infection (P<0.05).

Conclusion: The prevalence of S. mansoni infection was considerable in the study area. Four freshwater snails with a potential of transmitting disease in humans and livestock were identified. Further research and monitoring are essential to comprehensively investigate the factors contributing to the absence of human schistosome cercariae in the hatching results of Biomphalaria snails and to assess the potential impact on schistosomiasis transmission in the region. It is highly recommended to conduct a longitudinal study incorporating molecular techniques to analyze Biomphalaria infection rates and their susceptibility to schistosome infection.