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Various bat species often occupy the same habitats. Cohabitation should induce different preferences in spatial or trophic components of the bat ecological niche to reduce their competition. This determines the differences in the trematode fauna of Myotis spp. The purpose of our research was to study the biodiversity of trematodes in syntopic populations of five Myotis species in the Samarskaya Luka National Park. In the 2005–2007 period, we studied 867 bat specimens via the methods of complete helminthological dissection. In total, 11 trematode species from the families Plagiorchiidae (Plagiorchis koreanus, P. mordovii, P. muelleri, and P. vespertilionis), Pleurogenidae (Parabascus duboisi), and Lecithodendriidae (Prosthodendrium ascidia, Pr. chilostomum, Pr. cryptolecithum, Pr. hurkovaae, Pr. longiforme, and Lecithodendrium linstowi) were found in five Myotis species. Only three trematode species, P. koreanus, Pr. chilostomum, and P. duboisi, are common to all studied Myotis spp. Prosthodendrium cryptolecithum was recorded for the first time in Russia. Trematode species diversity is higher in Myotis daubentonii and M. dasycneme. The trematode fauna of M. brandtii, M. nattereri, and M. mystacinus is less diverse. The determining factor in the infection of bats with trematodes is feeding on semi-aquatic insects, possible second intermediate hosts of the parasites. The infection of bats with flukes occurs at different levels of host (Myotis spp.) abundance as a result of the realization of the main bat trophic relationships. Our results confirm the data that the ecological niches of the five Myotis species partially overlap. Analysis of the trematode fauna in Myotis spp. showed that, in the Samarskaya Luka, there may be weak competition for food items among bats.

Insectivores (Eulypotiphla) are a substantial component of Russian forest ecosystems. The parasites of these animals also form an important part of natural biocenoses and act as one of the factors in the formation of biodiversity. The Mordovia Nature Reserve and National Park “Smolny” are large, forested areas located in the center of European Russia. We studied the helminth fauna of insectivores in these protected areas in 2018–2022. In total, using the method of complete helminthological necropsy, we examined 478 individuals of shrews, moles, and hedgehogs and recorded 34 species of parasitic worms, i.e., 8 trematode, 7 cestode, 1 acanthocephalan, and 18 nematode species. The most diverse helminth fauna was found in Sorex araneus (22 species). The composition of helminths in S. isodon (12), Neomys fodiens (9), Sorex minutus, and Erinaceus roumanicus (8 species each) turned out to be less diverse. The lowest species diversity of helminths was observed in Neomys milleri (3) and Talpae europaea (2 species). Taking into account the newly obtained data, we conducted a review of the helminth diversity in shrews, hedgehogs, and moles in the Middle Volga region. According to our literature data, the helminth fauna of insectivores in this region consists of 52 species, including 14 cestodes, 13 trematodes, 22 nematodes, and 3 acanthocephalans. Most of them belong to the Palearctic faunal complex (36 species). The helminth fauna of insectivores in the studied protected areas was compared with the helminth fauna of micromammals in other areas of the Middle Volga region. Our comparative analysis showed a high and average degree of similarity in the helminth fauna within individual species and genera of Eulipotyphla.

We studied the trematode fauna in land birds from the Republic of Mordovia (European Russia) in 2018–2022. In total, we identified 16 digenean species in 45 species of birds from the orders Passeriformes, Piciformes, Caprimulgiformes and Falconiformes. The trematodes Phaneropsolus micrococcus and Morishitum polonicum were recorded for the first time in the birds’ parasite fauna of Russia. We obtained the first data on helminths in Hippolais icterina and Ficedula albicollis from Russia and in Coccothraustes coccothraustes from the Middle Volga region. New host records resulting from our study include Brachylaima mesostoma from Coccothraustes coccothraustes; Urogonimus macrostomus from Sylvia atricapilla, Ficedula albicollis, Ficedula hypoleuca and Acrocephalus palustris; Plagiorchis maculosus from Ficedula albicollis and Hippolais icterina; and Lyperosomum alaudae from Ficedula hypoleuca. The common parasite of rallid birds Leucochloridium holostomum is recorded for the first time from Turdus merula in Russia. Taking into account the newly obtained data, we carried out a review of trematodes in land birds of the Middle Volga region, of which the Republic of Mordovia is a part. Currently, the list of land bird digeneans in the Middle Volga region includes 56 species. Among all the studied land birds, members of the order Passeriformes have the richest trematode fauna (33 species). The diversity of trematodes found in passerines is due to the large number of both individuals and species studied and the variety of habitats and diet preferences of these land birds. Most of the identified trematode faunas (47 species) are obligate parasites of land birds. Nine species parasitize land birds accidentally and/or facultatively. In the Middle Volga area, the fauna of trematodes is the most diverse in land birds of the Nizhny Novgorod region, where 31 species are revealed. Fewer species of trematodes are identified in birds from the Bashkortostan (20), Mordovia (17) and Samara regions (15). For the birds of Chuvashia and Tatarstan, only eight and one species of trematodes are known, respectively. Six trematode species, found in land birds, have veterinary and medical significance as potential pathogens of dangerous helminthiases.

The helminth fauna of the Northern white-breasted hedgehog Erinaceus roumanicus was studied in the Republic of Mordovia (Russia) for the first time. In total, 9 species of helminths were found in 23 studied hedgehogs: Trematoda—Isthmiophora melis, Strigea strigis (metacercaria); Cestoda—Hymenolepis erinacei; Nematoda—Aonchotheca erinacei, Physaloptera clausa, Crenosoma striatum, Physocephalus sexalatus (juvenile), Agamospirura minuta (juvenile); and Acanthocephala—Nephridiorhynchus major. Four parasite species (the trematode I. melis, nematodes P. sexalatus, A. minuta, and the acanthocephalan N. major) were found in hedgehogs for the first time in Russia. An overview of the helminth fauna of four species of Erinaceus hedgehogs inhabiting the Palearctic region is given. A total of 54 parasite species were recorded across Erinaceus europaeus, E. roumanicus, E. concolor and E. amurensis: 14 trematodes, 6 cestodes, 27 nematodes, and 7 acanthocephalans. Among all the studied species of hedgehogs, E. europaeus (35 species) and E. roumanicus (36) have the richest helminth faunas. The diversity of the parasite communities of Erinaceus spp. is due to the wide distribution and varied diet of these mammals. Most of the helminths found in hedgehogs are transmitted along trophic chains. Hedgehogs are the final hosts for 39 species of parasites. For 15 helminth species, Erinaceus spp. are paratenic hosts. The majority of the hedgehog’s helminth fauna is formed by host-specific parasites, of which there are 13 species. Most of the hedgehog’s parasites in the Palaearctic are facultative (non-specific) species that parasitize in various vertebrate species. The helminth fauna of Erinaceus hedgehogs is most studied in Russia and Belarus, where 17 species of parasites are found in each country. The comparative analysis of the helminth faunas of Erinaceus spp. from various regions showed, on the one hand, the originality of the helminth fauna of each hedgehog species and, on the other, the similarity of the helminth fauna of these insectivores from various countries of the Palaearctic. These features are caused by similar lifestyles and diet peculiarities of every hedgehog species in various regions of the Palaearctic. A total of 12 of the 54 helminth species found in hedgehogs have medical and veterinary significance as causative agents of dangerous helminthiasis.

An overview of the parasites, bacteria and viruses of Glis glis (Rodentia, Gliridae) inhabiting the Western Palearctic is given. A total of 85 articles published from 1895 to 2021 were reviewed and analysed in our study. According to the literature’s data, 104 species associated with G. glis are recorded: 4 viruses, 8 Protozoa, 6 Cestoda, 6 Trematoda, 4 Nematoda, 1 Heteroptera, 2 Anoplura, 39 Siphonaptera and 34 Acari. The most studied group is ectoparasites. To a lesser extent, parasitic worms in G. glis were studied. There is very little data about the dormouse protozoans and viruses. The most studied parasites, viruses and protozoans of G. glis are in Germany, where 21 species were noted. The largest number of parasites was found in the dormouse in Russia (22), but of two groups only: helminths and ectoparasites. Only 20 out of 104 parasite species recorded in G. glis are host-specific. Most parasites (60 species) found in G. glis have a Palaearctic and cosmopolitan distribution. Three viruses, six species of protozoa and three helminths have veterinary and medical significance as potential pathogens of dangerous zoonoses. Also, many species of fleas, mites and ticks found on G. glis are vectors of a number of dangerous vector-borne diseases in humans and domestic and wild animals.

Nematodes of the genus Oswaldocruzia are common parasites of the small intestine of amphibians and reptiles. Our recent molecular analysis of Oswaldocruzia nematodes revealed that only Oswaldocruzia filiformis, which possesses high morphological variability, parasitizes amphibians and reptiles in European Russia. Here we present the study of Oswaldocruzia nematodes from the European green toad Bufotes viridis (Anura, Bufonidae) collected at different localities of the Middle Volga region in 2018–2022. We analyzed the morphological characteristics of the Oswaldocruzia spp. taxonomy together with novel molecular phylogenetic data. The data on phylogenetic analysis (based on partial CoxI mtDNA gene sequences) showed that Bufotes viridis is parasitized by two Oswaldocruzia species, the host-specific parasite Oswaldocruzia ukrainae and species generalist Oswaldocruzia filiformis. Broad morphological variability was revealed in O. ukrainae nematodes both from the same host specimen and from various toad individuals from different localities. Our results highlight the need for further biodiversity research of morphologically similar Oswaldocruzia species from amphibians and reptiles in the Western Palearctic using molecular genetic methods.

Morphological variability of trematodes from bats (Chiroptera) is poorly studied. Since the variability of adult digenean specimens may be rather high, morphological features are often insufficient for the identification of closely related species, and confirmation with the use of molecular data is required. The aim of our study was to combine the morphological and molecular phylogenetic analyses of several bat trematodes from the genera Gyrabascus and Parabascus (Pleurogenidae): Gyrabascus amphoraeformis, Gyrabascus oppositus, Parabascus lepidotus, Parabascus duboisi, and Parabascus semisquamosus, of which G. amphoraeformis and G. oppositus are little known in European Russia. We made detailed morphological descriptions of these trematodes from several definitive hosts, analyzed morphometric features, and generated new partial sequences of the 28S rRNA gene. A broad variability of trematodes of the genera Gyrabascus and Parabascus was revealed both from various host species and from specimens of the same host species. We propose a new taxonomic key for the identification of the studied species. Certain host specificity of these trematodes was revealed.

The taxonomic status of many species of the family Cyclocoelidae is still unclear. Two species of cyclocoelids, Harrahium obscurum and Morishitium dollfusi, were collected from the air sacs of birds (Turdus merula and Tringa ochropus) inhabiting the Middle Volga region (European Russia). Here, we provide the first detailed morphological description of these cyclocoelids and combine it with the first molecular phylogenetic analysis of Cyclocoelidae from birds in Russia based on partial sequences of their 28s rDNA and coI mtDNA genes. Specimens of both flatworm species from different host individuals differ slightly in body shape and size, which probably reflects host-induced intraspecific variability. For the first time, we have shown that a stable morphological character such as the length of the vitelline fields in the studied digeneans is variable at the species level and cannot be used in their morphological diagnosis.

In this study, we present our dataset containing up-to-date information about occurrences of trematodes in small mammals in the Middle Volga region (European Russia). The dataset summarizes micromammals’ trematode occurrences obtained by long-term field helminthological studies of soricomorphs, erinaceomorphs, bats and rodents during a period of more than 20 years (1999–2022). Our studies of trematodes in micromammals were conducted using the method of complete helminthological necropsy. The dataset includes 7470 records of trematode occurrences in micromammals with 4483 digenean records in Samara Oblast, 2986 records in Republic of Mordovia and one trematode record in Ulyanovsk Oblast. Our dataset presents the data on 43 trematode species from 21 genera and 9 families found in the region studied. The data on trematodes from 28 species of micromammals belonging to 14 genera are presented. In total, the number of collected trematode specimens in our dataset is 153,050. Each occurrence record contains the trematode species name, basis of record, locality of finding, host species, site in host, date and authors of the record and species identification. All occurrence records are georeferenced. The dataset is based on the research of the staff of the Institute of Ecology of the Volga River basin of RAS and the Joint Directorate of the Mordovia Nature Reserve and National Park “Smolny”. The distribution and diversity of trematodes of small mammals in the Middle Volga region has not been completely studied, and further investigation may reveal both new occurrences of trematodes and new host records.

We have conducted the first study of trematodes in wetland birds of the Samara region (European Russia). A total of 25 trematode species from 12 families were identified in 8 species of birds. Eight digenean species (Echinochasmus beleocephalus, Petasiger radiatus, P. exaeretus, Metorchis xanthosomus, Uroproctepisthmium bursicola, Leyogonimus polyoon, Hysteromorpha triloba, Cyathocotyle prussica) were registered for the first time in birds of the Middle Volga region. The first data on helminths in Ardea cinerea, Fulica atra, Phalacrocorax carbo, Larus cachinnans and Cygnus olor inhabiting this territory were obtained. Fifteen species of trematodes we found have veterinary significance as causative agents of dangerous helminthiases.