Soil contamination with parasitic helminth ova and larvae in the districts of Gampaha and Colombo in Sri Lanka; A preliminary survey

Abstract

Despite Sri Lanka's success in controlling human soil-transmitted helminthiases through mass deworming and improved sanitation, widespread soil contamination from animal excreta remains a public health risk, for toxocariasis and cutaneous larva migrans. This study aimed to determine the prevalence of parasitic helminth eggs and larval stages in soil in selected public areas of Gampaha and Colombo districts. Sampling locations were selected randomly; four sites were sampled at each location. Fifty-six soil samples were collected during May-September 2024 from parks (n=8), temples (n=4), university-grounds (n=12), roadside (n=4), school-grounds (n=12) and home-gardens (n=16). The samples were processed using the Magnesium sulphate flotation and Baermann technique for detection of helminth ova and larvae respectively. Identification of parasitic stages was based on morphological appearance under light microscopy at 40x10 magnification. Species diversity was calculated using the Shannon-Weiner diversity index and compared in wet and dry soil samples using the two sample t-test. The prevalence of parasitic helminth stages in soil samples was 37.5% (n=21). Ova of Toxocara spp. (n=8, 38.1%), Ascaris lumbricoides (n=2, 9.5%) and hookworm (n=1, 4.8%) and hookworm larvae, probable Ancylostoma spp. (n=10, 47.6%) were detected. Soil contamination was relatively high in temples (n=2, 50%), parks (n=3, 37.5%), and schoolgrounds (n=3, 25%). Species diversity was moderate (H’=1.56) with no significant difference between dry and wet soil samples (P=0.406; P>0.05). Contamination of soil with human and animal pathogenic parasite stages specially in public areas such as temples and children’s parks indicates the risk of exposure to these pathogens while at play or walking barefoot. Regular deworming of pets and controlling stray animal populations are recommended.