Parasitic Contamination of Soil in the Southern United States

Abstract

Parasites are generally associated with lower income countries in tropical and subtropical areas. Still, they are also prevalent in low-income communities in the southern United States. Studies characterizing the epidemiology of parasites in the United States are limited, resulting in little comprehensive understanding of the problem. This study investigated the environmental contamination of parasites in the southern United States by determining each parasite's contamination rate and burden in five low-income communities. A total of 499 soil samples of approximately 50 g were collected from public parks and private residences in Alabama, Louisiana, Mississippi, South Carolina, and Texas. A technique using parasite floatation, filtration, and bead-beating was applied to dirt samples to concentrate and extract parasite DNA from samples and detected via multiparallel quantitative polymerase chain reaction (qPCR). qPCR detected total sample contamination of Blastocystis spp. (19.03%), Toxocara cati (6.01%), Toxocara canis (3.61%), Strongyloides stercoralis (2.00%), Trichuris trichiura (1.80%), Ancylostoma duodenale (1.42%), Giardia intestinalis (1.40%), Cryptosporidium spp. (1.01%), Entamoeba histolytica (0.20%), and Necator americanus (0.20%). The remaining samples had no parasitic contamination. Overall parasite contamination rates varied significantly between communities: western Mississippi (46.88%), southwestern Alabama (39.62%), northeastern Louisiana (27.93%), southwestern South Carolina (27.93%), and south Texas (6.93%) (P <0.0001). T. cati DNA burdens were more significant in communities with higher poverty rates, including northeastern Louisiana (50.57%) and western Mississippi (49.60%) compared with southwestern Alabama (30.05%) and southwestern South Carolina (25.01%) (P = 0.0011). This study demonstrates the environmental contamination of parasites and their relationship with high poverty rates in communities in the southern United States.

Figure 1.

Map of communities and their respective poverty rates. Quintiles of poverty rates were retrieved from the 2019 American Community Survey and displayed around the time of soil sample collections.

Figure 2.

Overall parasite contamination rate (%, blue bars) and poverty rates (%, black dots) by community. There was a significant difference in the contamination rate between the communities (P <0.0001). The contamination rate was calculated as number of positive samples/total number of samples tested × 100%. Samples for any parasite tested were considered positive for the overall parasite contamination rate. Community poverty rates were obtained from the 2019 American Community Survey by the U.S. Census Bureau.

Figure 3.

Toxocara spp. contamination rate (%, blue bars) and poverty rates (%, black dots) by community. There was a significant difference in the contamination rate between the communities (P <0.0001). The contamination rate was calculated as number of positive samples/total number of samples tested × 100%. Samples positive for T. cati or T. canis were considered positive for the Toxocara spp. contamination rate. Community poverty rates were obtained from the 2019 American Community Survey by the U.S. Census Bureau.

Figure 4.

Normalized Toxocara cati burdens (fg/µL of DNA per kg of soil) by the community. T. cati burdens were significantly greater for communities with higher poverty rates (P = 0.0011). Community poverty rates were obtained from the 2019 American Community Survey by the U.S. Census Bureau.