Brachylaima succini sp. nov. (Trematoda: Brachylaimidae) from Succinea lauta, an amber snail in Hokkaido, Japan

The first record of Brachylaima ezohelicis (Trematoda: Brachylaimidae) in the red fox (Vulpes vulpes schrencki)

Brachylaima spp. are trematodes that have a unique life cycle as they exclusively use land snails as the intermediate host. Although their intermediate host has been well studied, very little information is available about their definitive host, partly as isolation of its adult stage from wild animals is rare. We found three trematodes in the small intestine of a red fox (Vulpes vulpes schrencki) in Hokkaido, the northernmost island of Japan. The trematodes were identified as Brachylaima ezohelicis based on morphological features and genetic analysis, which is believed to have a definitive avian host. The morphological features of the isolated trematodes were consistent with B. ezohelicis samples grown in the definitive host except for body length. Our study suggests that B. ezohelicis uses mammals as definitive hosts as well as birds.

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.

Emerging helminthiases of song thrush (Turdus philomelos) in Central Europe

Turdus philomelos is a common Western Palearctic thrush species of forests and agricultural landscapes, where it relies on the presence of hedgerows, patches of trees, and shrubs. In the present study, we address long-term changes in component communities of trematodes in T. philomelos across the timespan of over half a century. Based on our preliminary observations, we hypothesized that component communities of trematodes in T. philomelos in the study area are more diverse and species-rich compared with several decades ago. In the 1961-2019, we performed full-body necropsies of T. philomelos, which originated from the southern Czech Republic, and examined them for the presence of trematodes. We compared the trematode species richness and diversity of the analyzed component communities. The number of trematode species per host steadily increased in time in adult females and males. In juveniles, the highest numbers of trematode species per host were reached already in 1961-1990, then dropped and slowly raised up again in the latter time periods. The newly accumulated evidence suggests that trematodes with intermediate hosts previously restricted to T. philomelos wintering grounds increased in abundance in the study area. Some of them (Morishitium polonicum, Psilotornus confertus) sporadically appeared in juveniles or first-year birds, from which they were previously completely absent. Some of the spreading species, such as Lutztrema attenuatum, are present in high prevalence and high intensities of infection. Yet unknown part of observed changes could be related to changes in food composition; however, direct evidence for changes in T. philomelos diet is lacking despite clear evidence for a decline in earthworms in agricultural landscapes.