Objective of research: to investigate the clinical features of acute opisthorchiasis in rabbits. Materials and methods: Clinical evidence of acute opisthorchiasis in rabbits, laboratory blood tests. Results and discussion: Skin lesions in the form of cracks and ulcers of various sizes in the neck, thoracic back and croup, mostly localized along the spine, were clinically identified in acute opisthorchiasis of rabbits. Weight loss within the first month was up to 300 — 500 grams. Laboratory tests showed that one month later, the level of blood glucose in the infected animals was 3 times higher than in controls. Compared with the controls, a reduced number of red blood cells and hemoglobin level in animals of the experimental group was observed, leukopenia was determined. The blood coagulation time was significantly accelerated.

A morphometric study of liver changes at different invasive doses was conducted in rodents (Oryctolagus cuniculus). In a comparative aspect, the thickness of connective tissue formed around the portal tracts and the thickness of cellular infiltrates in the same area were studied at an invasive dose of 100, 50 and 10 metacercariae of Ophistorchis felineus (Rivolta, 1884). The experiment was conducted on sexually mature male rabbits at the age of 6 months, in each observation group of 10 individuals. Clinically healthy animals were infested with Ophistorchis felineus per os metacercariae once. The intermediate stage of the parasite was isolated from a dead fish (ide, Leuciscus idus (Linnaeus, 1758) and dace fish, Leuciscus leuciscus) obtained from the Tom River in Tomsk. The invasion that took place after 1 month was confirmed by a positive analysis of feces for parasite eggs by the Ragaser and KatoMiura methods. The animals were sacrificed after 5 weeks from the period of infestation. Histological preparations of the liver were made, stained with hematoxylin and eosin, according to Van Gieson. Histological preparations were studied by light microscopy with morphometry. The results obtained characterize a twofold change in the morphometric parameters of connective tissue thickness and cellular infiltration around the portal tracts of the liver lobes with an increase in the invasive dose.

Human economic activity leads to a significant redistribution of natural radionuclides in the environ-ment. Radiation background in buildings is considered as one of the main types of radiation exposure on the population, since a person spends most of his time indoors. Currently, with the adoption of federal laws: “On the radiation safety of the population” No. 3-FZ 09.01.1996, “On the Sanitary and Epidemiological Welfare of the Population” No. 52-FZ 30.03.1999, and also on the “Radiation Safety Standards "(NRB-99/2009)," Basic Sanitary Rules for Ensuring Radiation Safety "(OSPORB-99/2009), approaches to the organization of radiation control in the construction industry and, consequently, to the organization of radiation safety con-trol of the population, have changed in many ways. The article deals with the problems of ensuring radiation and environmental safety in the construction of buildings.The need for research on the radiation-ecological characteristics of buildings is shown. An important problem for the construction industry is the radiation and hygienic support of technological processes and construction. In many ways, the solution of the problems related to improving of the radiation safety of building complexes depends on the implementation of legisla-tion connected with population restrictions from exposure of natural radionuclides. The results of large-scale studies of the effective specific activity of natural radionuclides in building materials and industrial waste produced and used in the Volgograd region are presented in this article. It has been established that con-struction materials produced in the Volgograd region, in accordance with national legislative and regulatory requirements, belong to class 1 and can be used for the construction of residential and public buildings. There have been presented the results of the survey on the radon content in the air of residential buildings from various building materials, as well as the density of radon fluxes from the soil. Radiation monitoring of construction sites is necessa ensure the radiation safety of the population.

Тhymus (thymic, thymus gland) provides antigen-independent differentiation of lymphocytes, providing processes of cellular and humoral immunity in peripheral immune organs. After the onset of puberty, age-related involution of the organ occurs. Changes of thymus in parasitic invasions are found in the literature only for some types of pathogens, mainly of cestodosis group. No data on the influence of trematodes including Opisthorchis felineus (Rivolta, 1884) on thymus and its involution were found. Morphological study of the thymus was conducted at the invasion of Opisthorchis felineus (Rivolta, 1884) 1 month after infestation, in an invasive dose of 50 metacercariae. Microslides were studied by light and immersion microscopy, descriptive and comparative morphology. The design of the experiment divided the animals into two groups: the observation group consisted of invaded animals (Oryctolagus cuniculus) (n=10) and the control group (n=10). The results obtained were characterized by pronounced morphological signs of age involution in Opisthorchis felineus (Rivolta, 1884) infestation, compared to the control, including a decrease in the volume of the medulla, replacement of the fatty tissue by lobules, an increase in the number of Hassall's corpuscle. These changes characterize earlier aging of the organ in case of parasitic disease.

For the first time, we have studied the morphological picture of changes occurred in the spleen during invasion by Opisthorchis felineus (Rivolta), which was simulated in large rodents (rabbits). The experiment was performed on 16 animals infected orally with 50 metacercaria each. Histological sections of the spleen were made and stained with hematoxylin-eosin and by Van Gieson’s stain. Histological preparations were studied by the light microscopy method with morphography and morphometry, and the data obtained were processed statistically. There were morphological characters found of moderate stromal fibrosis, as well as infiltration of the mantle zone of lymphoid follicles by mast cells with partially degranulated cytoplasm, and areactive follicles as related to reactive ones which were exceeded by three times. Homogeneous islands of oxyphilic substance were found in the stroma. Thus, in the course of the experiment, morphological changes were found in the spleen invaded by Opisthorchis felineus (Rivolta), which were manifested in the organ fibrosis due to the moderate collagenogenesis through active fibroblasts. The lymphoid tissue of the white pulpa was characterized by inhibited formation of germinal centers in the most lymphoid follicles. The stromal component reconstruction with the displacement of lymphoid tissue was noted. Mast cells in the white pulpa characterize inflammatory and allergic reactions.