Modelling local and regional spatial distribution patterns of Toxocara canis eggs using spectral indexes

Abstract

Soil contaminated by Toxocara spp. eggs is considered as one of the main infection sources of Toxocariasis worldwide. In this study, we developed with a maximum entropy model (MaxEnt) a local and regional simulation for predicting the spatial patterns of Toxocara spp. eggs in soil in urban parks of Mexicali, Baja California Mexico, based on a remotely sensed Normalized Difference Vegetation Index (NDVI), an indicator of vegetation greenness, Normalized Difference Water Index (NDWI) and Earth Surface Temperature (EST). 56 public parks were sampled during a year (2016-2017). Flotation technique was used for the determination of Toxocara eggs contamination in soil samples. 54% of the parks were positive to helminths eggs. The regional model includes all urban areas, the local model represents one single park. Our findings indicate that NDVI is the variable with more contribution for the survival of the parasite. The probability of favorable conditions for the existence of Toxocara spp. is 89% in green spaces. It is documented that Toxocara eggs survive up to two years in humid, clayey and grassy conditions, being sensitive to direct sunlight. Due to the climate of the city of Mexicali, it is thought that there is a minimum presence of this organism. However, Toxocara spp. has been reported in July, where temperatures exceed 35 °C. This validates that vegetation, regardless of temperature contributes in a greater measure to its presence.

Keywords: Soil contamination, spectral indexes, Toxocara spp., maximum entropy, parks.