The article provides data on the epidemiological situation on parasitic diseases in the Russian Federation in the period from 2010 to 2021. The main trends in the activity of the epidemic process of the five main parasitosis (enterobiasis, giardiasis, ascariasis, opisthorchiasis, diphyllobothriasis) were revealed.

Introduction. Persons of the older age group, due to weakened immunity, are at risk for toxoplasmosis: with age, the level of seropositivity and the risk of reactivation of infection in people with chronic infection increases. But in clinical and epidemiological terms, this group has not been sufficiently studied.

Purpose of the study. Determination of the level of seropositivity and the degree of activity of toxoplasma invasion in persons of the older age category without pathology, as well as in combination with psychoneurological symptoms or transplantation of solid organs.

Materials and methods. The ELISA method was used to determine various classes of antibodies to T. gondii in the blood sera of 614 people aged 60 to 93 years (conditionally healthy individuals, patients with neuropsychiatric pathology, with cognitive decline, after organ transplantation).

Results. IgG antibodies to T. gondii were detected in 51,5 % of the examined people. There was a trend of increasing infection from the age of 60-64 years to 75-79 years. Very few cases of acute toxoplasmosis have been identified; more significant was the detection of IgA antibodies, a reactivation marker, in 10,1 % of the examined antibodies. The largest number of individuals with IgA was observed in patients after transplantation, with neuropsychiatric pathology and cognitive decline.

Discussion. Since toxoplasmosis is a latent infection of the brain and its association with a number of mental and neurodegenerative diseases has been proven, the high T. gondii infection in elderly people and the presence of reactivation markers in them suggests systematic monitoring of invasion, especially when combined with CNS pathology and reduced immunity. People aged "60+" with a certain clinical history are at risk in the presence of a parasite in the body.

Conclusion. Finding an association between toxoplasmosis and psychiatric disorders in immunocompetent individuals is the basis for further monitoring of such associations with a view to their prevention and treatment.

The article presents materials on the formation of emergent states of the "parasite–host" system in superinvasive opisthorchiasis (SO) under the influence of endogenous signaling molecules. The original scheme of endometriosis in OS is presented, the morphogenesis of uterine leiomyomas is traced as a result of exclusively endogenous signaling molecules, the development of endometrial cancer is traced without connection with the development of ectopic endometrium. The patho– and morphogenesis of cholangioectases of intra– and extramural bile ducts is presented.

The article analyzes the results of studies on the first and second intermediate hosts of the clonorchosis pathogen in mountainous and coastal provinces of Northern Vietnam. Habitats of mollusks of the family Bythiniidae of the first intermediate hosts of Clonorchosis sinensis are identified. Infestation by C.sinensis larvae was detected only in clams Parafossarulus striatulus in Thác Bá reservoir 0.1% of cases. Infestation of fish with cysts of this trematode was found in 6 of 12 studied provinces. The most favorable conditions for the formation and functioning of clonorchosis foci are created in the floodplain of the Hôngkha River and its tributaries in the central and coastal provinces of North Vietnam.

For experimentally infected rats with Trichinella spiralis (Owen, 1835) Railliet, 1895, spleen and bone marrow are shown to play an important role in the host immune responses.

We have studied a role of plasma cells in formation of protective responses for experimental Trichinella infection of white rats. It's been established that a degree of immunological transformation directly depended on a stage of Trichinella spiralis in the host. A stimulating effect of Trichinella has been shown at early intestinal and early muscular stages of the parasite's development. In these periods, high levels of blast cells with mitoses and high number of plasma cells were noticed. A suppressive effect of Trichinella at migration stage was accompanied by decrease of proliferation level and numbers of plasma cells, leading to suppression of the host immune response. Also, a sinusoid-like flow of plasmacytic reaction and mitotic activity of spleen cells had been noted.

During studies of morphological composition of peripheral blood increase in eosinophils' numbers was noted. This fact may be explained by the migration of Trichinella larvae, which may cause defensive reactions in the host (eosinophils are excreted into blood).

There is relatively little information on the effect of probiotic supplements used in helminthiasis, and one can only guess how much probiotics can affect helminthiasis and associated inflammatory and immunopathological changes in the gastrointestinal tract, as well as how parasitosis can affect the properties of probiotic preparations. The aim of this study was to study the effect of Giardia and Cryptosporidium on the intestinal microbiota of experimental animals in the study of probiotics. In the intestinal microbiota of experimental mice with successfully integrated probiotic strains of Lactobacillus sakei and Lactococcus lactis, cryptosporidium and giardia, which may indicate the antagonistic effect of cryptosporidium and giardia did not find these strains after protozoal invasion against these strains.

The article presents an analysis of statistical data on the incidence of the most common parasitic disease in the Russian Federation - enterobiasis. The source of statistical information was data from the Unified Interdepartmental Information and Statistical System (EMISS), taken from 2009 to 2022. Information and Statistical System (EMISS), taken from 2009 to 2022. According to the results of the study, a trend towards a decrease in the incidence of enterobiasis is clearly visible. A sharp decline in incidence by 40 % was recorded in 2020, which may be due to quarantine measures of the new coronavirus infection Covid-19. The highest incidence was recorded in 2009 and amounted to 187.84 people per 100 000 population. A number of other more extensive studies of the impact of Covid-19 on the growth or decline of other infectious and parasitic diseases are needed.

The review presents current data on the epidemiology, diagnosis, interaction between the parasite and the host, the pathology of dracunculiasis with a description of rare cases of atypical course of the disease. The current status and future prospects for vector control and elimination strategies are also described. The information collected in this article is presented to raise the awareness of medical professionals in order to quickly diagnose and effectively treat patients, as well as to prevent invasion of both humans and animals.