Bioclimatic analysis and spatial distribution of fascioliasis causative agents by assessment of Lymnaeidae snails in northwestern provinces of Iran

Abstract

Background: Snails of the Lymnaeidae family are the intermediate hosts of Fasciola species, the causative agents of fascioliasis. The purpose of this study was to determine the prevalence of Fasciola species in lymnaeid snails and to investigate the association of geoclimatic factors and Fasciola species distribution in northwestern provinces of Iran using geographical information system (GIS) data.

Methods: A total of 2000 lymnaeid snails were collected from 33 permanent and seasonal habitats in northwestern Iran during the period from June to November 2021. After identification by standard morphological keys, they were subjected to shedding and crushing methods. Different stages of Fasciola obtained from these snails were subjected to the ITS1 polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for species identification. The associations of weather temperature, rainfall, humidity, evaporation, air pressure, wind speed, elevation, and land cover with the distribution of Fasciola species were investigated. Geographical and statistical analysis was performed using ArcMap and SPSS software, respectively, to determine factors related to Fasciola species distribution.

Results: Of the 2000 snails collected, 19 were infected with Fasciola hepatica (0.09%), six with F. gigantica (0.03%), and 13 with other trematodes. Among geoclimatic and environmental factors, mean humidity, maximum humidity, and wind speed were significantly higher in areas where F. hepatica was more common than F. gigantica. The altitude of F. hepatica-prevalent areas was generally lower than F. gigantica areas. No significant relationship was observed between other investigated geoclimatic factors and the distribution of infected snails.

Conclusions: The present study showed the relationship of humidity and wind speed with the distribution of snails infected with F. hepatica or F. gigantica in the northwestern regions of Iran. In contrast to F. gigantica, F. hepatica was more prevalent in low-altitude areas. Further research is recommended to elucidate the relationship between geoclimatic factors and the presence of intermediate hosts of the two Fasciola species.

Keywords: Fasciola; GIS; Iran; Lymnaeid snails; PCR.

Fig. 1

Geographical location of the sampling areas for lymnaeid species in Iran. The provinces surveyed for this study are shown in dark green

Fig. 2

PCR–RFLP pattern of the ITS1 gene of Fasciola spp. in infected snails: F. gigantica (lanes 2, 4, 5, 8, 9) and F. hepatica (lanes 3, 6, 7, 10, 11), 100-bp DNA size marker (lane 1), and negative control (lane 12)

Fig. 3

Climate interpolated raster maps: minimum air pressure (a), maximum air pressure (b), mean air pressure (c), minimum temperature (d), maximum temperature (e), mean temperature (f), minimum humidity (g), maximum humidity (h), mean humidity (i), soil temperature (j), rain (k), dew temperature (l)

Fig. 4

Maps of the environmental factors: digital elevation model (a) and land cover (b)