Trematódeos transmitidos por moluscos gastrópodes no Rio São Francisco em Januária, Minas Gerais, Brasil

Abstract

The present study aimed to evaluate the transmission of digenetic trematodes transmitted by mollusc in the São Francisco River, in Januária city, State of Minas Gerais, Brazil. Malacological surveys were carried out on the riverbank and nearby aquatic collections, between July 2017 and August 2019. A total of 11,690 specimens of gastropod molluscs belonging to nine species were collected and evaluated. From them, 369 (3.16%) were found infected with larval trematodes. Initially, cercariae were studied morphologically under an optical microscope to determine cercarian types. When possible, experimental infection studies were carried out with the larvae in order to obtain other developmental stages (metacercariae and adult). Other organisms from the same area, such as Odonata larvae (n=21), tadpoles (n=78) and fish (n=160), were also examined for infection with trematodes. Additionally, genetic sequences of 28S, ITS1-5.8S-ITS2, cox1 and nad1 genes were obtained for most species of trematodes found (29/31), which were used for identification and phylogenetic analysis. This integrative taxonomic approach revealed the occurrence of 31 species of trematodes in gastropod molluscs from the locality. The highest trematode diversity was verified in Biomphalaria straminea, which was found infected with16 species of these parasites (Aporocotylidae gen. sp. 1, Austrodiplostomum compactum, Clinostomum heluans, Cotylurus sp., Drepanocephalus sp., Echinostoma sp., Echinostomatidae gen. sp., Hysteromorpha sp., Notocotylidae gen. sp., Parastrigea sp., Ribeiroia sp., Schistosomatidae gen. sp. 1, Schistosomatidae gen. sp. 2, Spirorchiidae gen. sp, Tylodelphys sp. and Zygocotyle lunata). In two other planorbids, Ancylinae gen. sp. and Biomphalaria occidentalis, it was verified the infection with larvae of Choledocystus sp. and Spirorchiidae gen. sp., respectively. The native thiarid Aylacostoma tuberculatum was found infected with 11 species of trematodes (Aporocotylidae gen. sp. 2, Cryptogonomidae gen. sp., Echinochasmidae gen. sp., Lecithodendriidae gen. sp. 1, Lecithodendriidae gen. sp. 2, Neocladocystis sp., Phaneropsolidae gen. sp., Philophthalmus sp. nov., Pseudosellacotyla lutzi, Stephanoprora sp. 1 and Stephanoprora sp. 2). Cercariae of four trematode species (Heterophyidae gen. sp., Lecithodendriidae gen. sp. 1, Phaneropsolidae gen. sp and Philophthalmus sp. nov) were found in Aylacostoma chloroticum. In the invasive thiarid, Melanoides tuberculata, it was detected the infection with Centrocestus formosanus. Among the organisms evaluated as potential second intermediate hosts for the parasites found in molluscs, it was detected in fish, the infection of Australoheros sp. with metacercariae of A. compactum and C. heluans, and Myleus pacu with Cryptogonimidae gen. sp. Moreover, B. straminea was found infected with metacercariae of Cotylurus sp. and Echinostomatidae gen. sp.; Odonata larvae with Phaneropsolidae gen. sp., and tadpoles of Rhinella sp. with Parastrigea sp. It is also noteworthy that Hoplias malabaricus was identified as the definitive host for P. lutzi. Additionally, developmental stages of other four trematodes (Apharyngostrigea sp., Crassiphialinae gen. sp., Posthodiplostomum nanum e Neocladocystis intestinalis) were found in fish, however, without identification of their first intermediate hosts. Thus, the different approaches used in this study enable to characterize the occurrence of a rich diversity of trematodes in molluscs in the São Francisco River, resulting in new hosts and parasites records, as well as in the elucidation of aspects of the life cycles and the identification of a new species of trematode. In addition, the molecular data obtained may support future studies aimed at advancing knowledge about the biology and taxonomy of this diverse but still poorly known fauna of trematodes that occurs in river environments from Brazil.