Soil-Transmitted Parasites and Non-Pathogenic Nematodes in Different Regions of Porto Alegre City, Brazil: A Comparison between Winter and Summer

We assessed the prevalence of soil-associated parasites and non-pathogenic nematodes in eight public areas of Porto Alegre (Rio Grande do Sul state, southern Brazil), the most populous city in Rio Grande do Sul. Soil samplings were carried out during the winter of 2022 and summer of 2023: A total of 80 samples were collected in winter and 80 in summer (ten samples from each sampling site per season), totaling 160 soil samples. The frequency of microscopic non-pathogenic nematode larvae was significantly higher (p = 0.048) in winter (93.75%) than in summer (82.50%). Considering the pooled data from winter and summer (n = 160) for human pathogenic parasites, the following frequencies were observed (using microscopy analysis): hookworm (filariform) larvae (1.25%), hookworm (rhabditiform) larvae (11.25%), Strongyloides spp. (filariform) larvae (0.63%), Strongyloides spp. (rhabditiform) larvae (2.5%), hookworm eggs (10.63%), Ascaris spp. eggs (10.00%), and Trichuris spp. eggs (1.25%). Hookworm (rhabditiform) larvae were the most frequent parasitic structures (15.00%) in winter, and A. lumbricoides eggs were the most frequent parasitic structures (8.75%) in summer. No statistically significant difference was observed in the frequency of pathogenic parasites between the seasons (p > 0.05). Toxoplasma gondii DNA was assessed, but all soil samples tested negative in molecular analysis. Our results indicate that soil from many regions of Porto Alegre shows a high prevalence of soil-transmitted helminths, indicating the need for improvements in social conditions and environmental sanitation in the city. Our study also suggests that climate change may affect soil biodiversity, potentially harming non-pathogenic nematodes and favoring human pathogenic parasites.