A description of a new species of the genus Brachydistomum (Trematode, Dicrocoeliidae) from the Eurasian Tree Sparrow Passer montanus (Linnaeus) (Passeriformes) in Japan, with a report on the first intermediate host.

The trematode Brachydistomum suzume n. sp. (Dicrocoeliidae) was detected in the Eurasian Tree Sparrow Passer montanus, and described as a new species in Japan. This new species can be distinguished from the other members of the genus on the basis of morphological characters of suckers and reproductive organs. A partial sequence of adult mitochondrial cytochrome c oxidase subunit 1 (COI) was used as a DNA barcode, and dicrocoeliid sporocysts and cercariae detected from four camaenid land snail species, Bradybaena pellucida, Brad. similaris, Acusta sieboldiana and Euhadra brandtii, were molecularly identified as the new species. Phylogenetic trees of nuclear 28S ribosomal DNA and COI also showed the new species to be distinct from the other trematode species, including Brachydistomum spp.

Introducing the land snail Bradybaena pellucida increased infection risk of the avian parasite Postharmostomum commutatum in the Kanto region of Japan.

The trematode Postharmostomum commutatum is a parasite of the chicken Gallus gallus domesticus. Its heavy infection can cause inflammation and hemorrhage in the cecum of host birds. We found a severe infection of metacercariae of P. commutatum, which was identified based on DNA barcodes with morphology, in the introduced land snail Bradybaena pellucida and its related species in the Kanto region of Japan. Our field survey revealed that metacercariae were detected in 14 of 69 sampling locations in this region. B. pellucida was thought to be the major second intermediate host of metacercariae of the trematode because this snail was most frequently found in the study area and the prevalence and infection intensity were higher than those of the other snail species. The observed increase in metacercariae in introduced populations of B. pellucida can enhance the infection risk of chickens and wild host birds, probably owing to the spillback effect. Our seasonal field study showed that the prevalence and infection intensity of metacercaria seemed to be high in populations of B. pellucida during the summer and early autumn. Therefore, chickens should not be bred outdoors during these seasons to prevent severe infection. Our molecular analysis, based on cytochrome c oxidase subunit I sequences, showed a significantly negative value for Tajima's D in P. commutatum, suggesting an increase in its population size. Thus, P. commutatum distributed in the Kanto region may have increased its population size with the introduction of the host snail.

Brachylaima phaedusae n. sp. (Trematoda: Brachylaimidae) from door snails in Japan.

The metacercarial infections of door snails (Gastropoda: Clausiliidae) with unknown species of the genus Brachylaima (Trematoda: Brachylaimidae) have recently been reported in eastern Honshu and Kyushu, Japan. A large scale snail survey was carried out to clarify their taxonomic status. From the period of 2015 to 2020, a total of 1239 land snails (768 door snails and 471 others) were collected from 32 localities in Honshu, Shikoku, and Kyushu. The resulting trematode isolates were identified as Brachylaima sp. by mitochondrial DNA barcoding. The sporocysts were found only a few from Megalophaedusa sublunellata (Clausiliidae), Tauphaedusa subaculus (Clausiliidae), and Aegista trochula (Camaenidae), while the metacercariae were frequently detected from 14 species of Clausiliidae and 2 species of other families. Although Brachylaima sp. showed a broad range of intermediate hosts, door snails seem to be very important to drive the life cycle. The gravid adults of Brachylaima sp. was experimentally raised from metacercariae using immunosuppressed mice. Morphological, phylogenetical, and ecological considerations prompted us to propose Brachylaima phaedusae n. sp. for this unknown species. The definitive hosts of the new species are completely unknown. The wide geographic distribution and high genetic diversity of the new species suggest a possibility that the definitive host is ground-foraging birds, which prefer door snails.