Soil contamination by Taenia solium egg DNA in rural villages in Kongwa district, Tanzania

Abstract

The presence ofTaenia solium DNA from eggs in soils around the households in four Tanzanian villages in Kongwa district were analysed in relation to seasonal fluctuations and infection risk implications. A total of 192 pooled soil samples from five sampling points per household were examined by droplet digital Polymerase Chain Reaction (ddPCR) from 96 pigkeeping households both during the dry and rainy seasons. The pooled samples were first processed by a flotation-double sieving technique, followed by screening for worm DNA employing universal primers targeting the mitochondrial cytochrome c oxidase subunit I (cox1) gene of human taeniid species and some other helminths. All DNA positive samples were later confirmed by a specific ddPCR probe assay targeting the mitochondrial cox1 gene of T. solium. A total of 17.2% (n = 33) samples were positive with the universal ddPCR, whereas T. solium DNA was confirmed by the specific ddPCR only in 3.1% (n = 3) of the surveyed households. The detection of T. solium DNA in this study spells out a low risk of exposure to T. solium eggs from contaminated household soil. Based on our results, ddPCR seems to be a promising technology for screening T. solium eggs in soil.

Diagnostic tools for the detection of taeniid eggs in different environmental matrices: A systematic review.

“…Warm summer temperatures at the time of collection may therefore contribute to more rapid degeneration of eggs ( Scandrett et al, 2009 ; Bucur et al, 2019 ). In contrast, different records detected significantly more taeniid eggs in soil and vegetables during the dry season compared with cold ones ( Eraky et al, 2014 ; Fallah et al, 2016 ; Maganira et al, 2020 ). A possible explanation for this might be the frequent use of contaminated water for irrigation during spring and summer.…”

“… Sludge Quantitative N.M. Stored on ice until analysis 6 N.M. Bolivia Verbyla et al (2013a) a Verbyla et al (2013b) a Immunofluorescence test with monoclonal 4E5 antibody Echinococcus spp. Soil and sand Quantitative N.M. N.M. 9 7-8 h Kenya Craig et al, 1988 Sieving, drying, dilution (PBS + 0.3% Tween 20), microscopy, and Western blot E. granulosus Topsoil and sludge Qualitative N.M. In polyethylene bags at 4 °C until analysis N.M. N.M. Argentina Sánchez-Thevenet et al, 2019 Double sieving, ZnCl 2 flotation (s.g. 1.45) and ddPCR ( cox- 1) Taenia solium Soil Quantitative N.M. N.M. 5 N.M. Tanzania Maganira et al, 2020 Washing (PBS + Tween 20), ZnCl 2 flotation (s.g. 1.45) and dd PCR ( cox- 1) T. solium Clay, silt, sand and loam soil Quantitative Se: 13–36% N.M. 11 ≤ 48 h Tanzania Maganira et al, 2019 Washing (0.2% Tween 20), sieving centrifugation ZnCl 2 flotation (s.g. 1.42) and real-time qPCR ( rrnL ) E. multilocularis Soil Quantitative LOD: 1 egg/10 g Stored at −80 °C until analysis 11 ≤ 24 h France Umhang et al, 2017 Sieving, ZnCl 2 flotation (s.g. 1.4) and nested PCR (12S rRNA) E. multilocular...…”

“…Such low sensitivity might be attributed to losses during preparatory steps (washing, sieving, flotation), the absence of an eggshell disruption step to improve DNA-extraction, and/or the use of a DNA-extraction kit intended for blood and tissue samples. Specificity was not determined ( Maganira et al, 2019 , Maganira et al, 2020 ). Finally, for the simultaneous detection of, and differentiation between, T. solium , T. saginata, and E. granulosus in water and soil, a qualitative multiplex PCR with a sensitivity of less than 10 pg was developed by González et al (2002) .…”

“…In another record, the soil samples were obtained from the surface layer of the ground at a depth of less than 2 cm at several points within the space of a few meters ( Szostakowska et al, 2014 ). A final record specifying the sample's location aimed at detecting T. solium eggs in soil at a depth of 3 cm at different households within a village (the backyard, around the toilet, inside the house, in front of the house, and around the waste disposal area) ( Maganira et al, 2020 ). In other words, more research is needed to determine the optimal location and time of the sampling with the highest chance of detecting eggs.…”

Development of a dose-response model for porcine cysticercosis

“…Considering the possible importance of low doses of eggs in pig infection, novel methods with a limit of detection of 200 eggs per 200 g (1 egg per gram of sample (EPG)) validated by Gamboa et al . [ 50 ], and the Droplet Digital PCR with a limit of 10 eggs per 5 g (2 EPG) [ 51 ], would be recommended to evaluate T . solium eggs in the environment.…”