Investigating Environmental Determinants of Soil-Transmitted Helminths Transmission using GPS Tracking and Metagenomics Technologies

Abstract

Background: The Global Health community aims to eliminate soil-transmitted helminth (STH) infections by 2030. Current preventive methods such as Mass Drug Administration, WASH practices, and health education needs to be complimented to halt transmission. We tracked the movement of hookworm-infected and non-infected persons and investigated soil factors in the places they frequented within an endemic community to further understand the role of human movement and sources of infections.

Methods: 59 positive and negative participants wore GPS tracking devices for 10 consecutive days and their movement data captured in real time. The data was overlaid on the community map to determine where each group differentially spent most of their time. Soil samples were collected from these identified sites and other communal places. Physical and chemical properties were determined for each sample using standard methods and helminth eggs cultured into larvae using the Baermann technique. Bivariate and multivariate analyses were used to determine associations between larvae counts and soil factors. Helminth species were identified with metagenomic sequencing and their distributions mapped to sampling sites in the community.

Results: The study found that there was no significant difference in the average larvae counts in soil between sites assessed by infected and non-infected participants (P=0.59). However, soil factors, such as pH, carbon and sandy-loamy texture were associated with high larvae counts (P<0.001) while nitrogen and clay content were associated with low counts(P<0.001). The dominant helminth species identified were Panagrolaimus superbus (an anhydrobiotic helminth), Parastrongyloides trichosuri (a parasite of small mammals), Trichuris trichuria (whipworm), and Ancylostoma caninum (dog hookworm). Notably, no Necator americanus was identified in any soil sample.

Conclusion: This study provides important insights into the association between soil factors and soil-transmitted helminths. These findings contribute to our understanding of STH epidemiology and support evidence-based decision-making for elimination strategies.

Keywords: GPS tracking; Metagenomics; Soil-transmitted helminths; soil factors.

Figure 1:. Map of Ghana showing the Kintampo North Municipal area.

Kawampe is located on the main trunk road to the north of Ghana. Map created with ArcGIS 10.8 with shapefiles from https://www.diva-gis.org/gdata.

Figure 2:. Map of Kawampe showing the soil types at each sampled site.

Lima series (yellow dots) was found mainly to the north of the community while the Kumayili type (pink triangles) was widespread and to the southern part. Map created with ArcGIS 10.8

Figure 3:. 3A) 3-D illustration of all the participants’ movements across space and time.

The green patches were the areas where most participants were located, while the red and blue circles indicated the length of time both positive and negative participants spent within these green patches respectively. The 3B) 2-D plot illustrates the movement patterns of the positive group (red lines) and negative group (blue lines). Red triangles denote the sites frequented by infected individuals and where soil samples were collected, while blue triangles represent where negatives were mostly found. These triangles indicate the exact centers of the grids (green patches) in 3A.

Figure 4:

Soil factors significantly associated with high and low larvae counts.

Figure 5:. The distribution of dominant helminth parasites found in specific areas within the study community.

Parastrongyloides trichosuri (blue), Panagrolaimus superbus (green, Trichuris trichiura (yellow) and Ancylostoma caninum (red). The counts are in parentheses.