The article describes occurrence and distribution of Eustrongylides trematodes in fish in the waters of the Dnipro-Buh estuary and the delta of Dnipro River in Mykolaiv and Kherson Region. Study was conducted in 2015–2016. This parasite was found in natural water reservoirs in Mykolaiv and Kherson region in following fish species: Sander lucioperca (Linnaeus, 1758), Perca fluviatilis (Linnaeus, 1758) and Esox lucius (Linnaeus, 1758). Ichtyopathological investigation of 346 fishes was conducted. Parasites were observed in abdominal cavity, muscle tissue, wall of gastro-intestinal tract, gonads and hepatopancreas. P. fluviatilis was the most affected species, prevalence of infection was 85.1 %. Less infected were S. lucioperca and E. lucius, with the prevalence of infection 58.1 % and 58.9 % respectively. Mean prevalence of infection of predatory fish in studied reservoirs was 70.5 %. The intensity of infection was the highest in perch (1–14 nematodes per fish). The lowest intensity of infection was found in pike-perch (1–9 nematodes per fish).

The ecosystems that have developed in the exclusion zone after the accident at the Chernobyl nuclear power plant in 1986 have a number of features. Parasites, as part of an ecosystem, can act as indicators of the processes taking place in it. Mouse rodents play an important role in the preservation and transmission of pathogens of some, including zoonotic, diseases in the wild. Therefore, the study of parasites in murine rodents, especially those transmitted transmissively, makes it possible to understand the characteristics of the distribution and the level of threat of their transmission to other susceptible animals, including agricultural, small domestic animals and humans. We carried out a study of blood smears taken from murine rodents for the presence of pathogens of transmissible parasitic diseases. According to the results of the studies, the pathogen Hepatozoon spp. Was detected for the first time in Ukraine. in the population of murine rodents. Creating an exclusion zone is one of the most obvious and long-lasting consequences of the Chernobyl Nuclear Power Plant (CNPS) accident. Because of 90-95% of this territory lacks systematic human activity and regime equal to the reserve. Ecosystems formed in the exclusion zone are affected a number of key factors as radioactive contamination, succession, wills and climate change. Spatial heterogeneity of density, radionuclide composition and physical chemical forms of precipitation are a characteristic feature of radioactive pollution in the Chernobyl Zone. Much of the aquatic and terrestrial ecosystems in the Chernobyl Zone as of 1986 was an artificial or semi-artificial systems that were under the regulatory control of man. The removal of regulatory control has led to the inclusion of natural influences mechanisms. That is, a significant part of ecosystems is in a state far from equilibrium, where the processes of succession are active. The testamentary effect is the result of a radical economic contraction activities and the creation of a strict security regime. Given this dynamics ecosystems in the Exclusion Zone has a unique character. Parasites are part of the ecosystem, so they can act as indicators of the processes occurring in it. Mouse-like rodents play an important role in the preservation of agents some infectious diseases in the wild. It is known that rodents are reservoirs hosts at least 60 zoonotic diseases, playing an important role in their transmission and distribution. Not the last role in it is played by features biology and way of life of these animals. Study of parasites in murine rodents, especially those that transmitted transmissively, will make it possible to understand the peculiarities of distribution and the level of threat of their transmission to other susceptible animals, including agricultural, small pets and humans. The object of our study was blood smears taken from murine rodents: Apodemus agrarius, Apodemus flavicollis, Myodes glareolus and Apodemus spp. Catching mice for further sampling conducted at 3 three landfills. Mouse-like rodents are significantly affected by pathogens of infectious diseases, including those transmitted through blood-sucking arthropods. Therefore, the study of the presence and prevalence of transmissible agents in murine rodents is important in order to prevent the disease in other species of animals or humans. The purpose of the study was to study the role of rodents Chornobyl Excusion Zone as a reservoir of blood-borne diseases. The study was conducted during 2020-2021. Blood smears from rodents Apodemus agrarius, Apodemus flavicollis, Myodes glareolus and Apodemus spp, which were selected during the expedition from three landfills and transferred to the Department of Pharmacology, Parasitology and Tropical Veterinary Medicine of NULES of Ukraine, where they conducted further research. Blood smears were stained by the method of Romanowski-Gimza, Leuko-Diff and examined under an immersion microscope system. A total of 117 blood smears were collected from 117 murine rodents from three landfills. According to the results of microscopic examination in blood smears revealed parasites, which morphologically we attributed to Hepatozoon spp. This agent was detected in Ukraine for the first time. Agents had an oval body shape with a large nucleus and were located in the cytoplasm of leukocytes (mostly neutrophils, rarely lymphocytes). In total, hepatozoan agents were detected in blood smears from 13 studied animals, which was 11.11%. And the invasion of Hepatozoon spp. was found in murine rodents of the first landfill, in 7 rodents. The smallest of the murine rodents of the second landfill was found only in blood smears from 2 animals. In addition to hepatozoons in murine rodents, we also found agents of other diseases, such as Babesia spp., Rickettsia spp., Borrelia spp. and Trypanosoma spp.