A faunistic survey of snails and their infection with digenean trematode cercariae in Bandar-e Anzali at the littoral of the Caspian Sea.

Trematodes are known as a diverse group of endogenous parasites, which snails as their intermediate hosts can dramatically affect parasite transmission dynamics. Snails play a key role in life cycles of digenean trematode. However, there has not been much faunistic surveys in terms of snails' distribution in Iran. The current study was aimed to identify snail's fauna and their current geographic distribution in four regions of Guilan province, Iran. Several species of snails (land and freshwater snails) were obtained from 4 different areas (2018-2019), and then samples were separately transferred to the laboratory. Diagnosis of snails was then performed according to morphometric characteristics including dextral or sinistral shell, shape, color and size of shell. Moreover, radula was stained and then photographed under microscopic examination. Furthermore, 25% of any species were tested for cercarial infection. In total, 2082 snails belonging to 12 species were identified based on the morphological characteristics. Land snails were identified to be Helicella sp. (46.4%), Helix aspersa (34.1%), Helicopsis sp. (8%), Pomatia sp. (6.7%) and Oxyloma elegans (4.8%). Moreover, freshwater snails were Physa acuta (30.6%), Lymnaea auricularia (25.8%), Lymnaea gedrosiana (18.7%), Lymnaea palustris (8.9%), Lymnaea truncatula (8.1%), Planorbis sp. (6.4%) and Lymnaea stagnalis (1.5%). In collected snails, Lymnaea auricularia (0.66%) and Lymnaea gedrosiana (0.45%) were the only snails harboring cercariae (Gymnocephalus cercariae). There was no statistically significant difference between the cercarial infection and snail species (P<0.05). Comprehensive field studies are highly needed for better evaluation of the snail biodiversity in the Caspian Sea region due to the particular climatic conditions and the high prevalence of trematodosis.