Limnic gastropods and trematodes of public health concern in Barreirinhas, Maranhão State, Brazil.

Limnic gastropods are of great importance as both biodiversity components and public health threats. These organisms serve as vectors for some helminths that may be involved in the occurrence of human zoonoses. Previous studies carried out in the region of the Lençóis Maranhenses National Park (LMNP) reported the occurrence of gastropod species, including Biomphalaria glabrata (Say, 1818) and Biomphalaria straminea (Dunker, 1848), vectors of Schistosoma mansoni (Sambon, 1907), the causative agent of schistosomiasis. This study aimed to survey gastropod species occurring in the region to understand their diversity and geographical distribution. Another aim was to analyze the potential infection of these organisms by trematodes. The municipality of Barreirinhas experiences a large influx of people due to its importance as a Brazilian tourist hub in the LMNP. Four surveys were carried out in Barreirinhas. Based on reports from the population about mollusk occurrences, six bodies of water in the municipality were investigated, distributed in urban and rural areas. The collected specimens were identified using morphological methods and analyzed weekly for 45 days to detect trematodes. The survey carried out in Barreirinhas from October 2021 to August 2022 revealed the occurrence of mollusks of interest, totaling 1273 specimens of the species Melanoides tuberculata (Müller, 1774), Pomacea sp. (Perry, 1810), and B. straminea. The predominant species was B. straminea, with 777 specimens (61%), followed by M. tuberculata with 347 specimens (27.3%), and Pomacea sp., with 149 specimens (11.7%). Larvae of Xiphidiocercaria (Microphallidae) and Gymnocephala (Gymnophallidae) were found parasitizing Pomacea sp. Brevifurcate apharyngeate distome larvae were detected in B. straminea.