The results of the conducted studies reveal changes in the sows blood against the background of highly intensive esophagostomiasis invasion. In particular, significant quantitative changes in leukocytes amount in blood and the ratio of their individual species in the sick sows infested with esophagostomiasis was noticed as compared with the control group of animals. A decrease in the amount of leukocytes accompanied by leukopenia was observed in all infected animals, while the content of white blood cells was significantly lower than in the control 32.2% (p <0.001). This indicates, on the one hand, the expressed pathogenic effect of the causative agent of esophagostomiasis on the pigs body, and, on the other hand, – on the suppression of the reaction of this effect from the white blood cells.

At the same time, the esophagostomiasis invasion caused changes in the leukoformula of experimental animals, where was a noticeable (by 4 times) increase in the percentage of eosinophils, and their absolute number – by 2.75 times was noticed compared with the control. Also, probable changes were observed with regard to rod-nuclear neutrophils, which indicates a decrease by 0.6 times in the absolute number of these cells in the infested pigs compared with the control. A similar pattern was observed in relation to segmental neutrophils, the percentage and absolute number of which was smaller by 17% and 2429 cells, respectively, compared with the control (p <0.001). Some other quantitative changes have been found out regarding lymphocytes. In particular, their percentage was significantly higher (by 5%) in the infested animals as compared to the control, and the absolute number was 1077.3 cells (p <0.001) lower. In the macrophage series of cells that were represented by monocytes, no significant quantitative changes were found against the background of the invasion, although the absolute rates in the sick animals were slightly lower than in the control.

T-lymphocytes determination by socket-forming method showed that absolute number of T-lymphocytes was smaller – 824,937 ± 19,2 cells in 1 ml (p <0.001) in the esophagostomiasis sick animals patients and their percentage content was 25.4 ± 0.24 (p <0.001) compared with the control, which indicates depression in the cellular part of the immune system. On the contrary, the absolute level of B-lymphocytes in the infested animals was significantly higher than in control – by 333.8 cells in 1ml, and their relative content 17.2% higher, which indicates an increase in the activity of humoral immunity.

The level of bactericidal and lysozyme activity of serum in the infested sows was significantly lower than in the control non-infested animals – by 23% and 25.1%, respectively, which gives ground to assume the inhibition of nonspecific resistance against the background of esophagostomiasis invasion.

Phagocytosis indicators (phagocyte activity and phagocyte index) of blood neutrophils in esophagostomiasis sick piglets also appeared to be lower, respectively, by 15.6% and 2.17 units of activity against the control non-infested animals, which is a sign of inhibition of cellular mechanisms of nonspecific protection caused by parasitism of this helminthes pathogens.

Thus, our studies found out significant changes in white blood cells and in leukocyte formula in the blood of sows spontaneously infested with esophagostomas, which indicate inhibition of immune responses in the body of invaded pigs. In particular, there is a marked leukopenia, eosinophilia, neutropenia and lymphocytopenia, in all the animals infested with this helminthes, in comparison with control, which indicates the high pathogenic activity of esophagostomiasis agents, the products of their life and tissue disintegration, as well as allergic processes in the host's organism. Eosinophilia is known to be a reaction of the organism to the helminth antigens action, which causes release of histamine – a mediator of allergic inflammation. It is one of the forms of manifestation of allergy to helminthiasis and a peculiar indicator of the previous interaction of the antigen-antibody system.

In our opinion, the indicated changes in the blood of the sow pigs against the background of the esophagostomiasis invasion are caused by a long period of immunosuppressive action of the worms on the pig's body as well as depletion and decompensation of T-cell mechanisms, as well as by the non-sterile immunity typical in most helminthiasis.

The reason for such an assertion is a number of scientific papers, which prove that the causative agents of helminthiasis are related to immune mechanisms of bilateral action. On the one hand, they stimulate immunity, resulting in a number of phenomena of cellular and humoral immune responses, and on the other they cause inhibition of functional and proliferative activity of cells of lymphoid tissue, which results in the development of secondary immunodeficiencies and abrupt changes in the relationship in the host-parasite system and ensures the survival of the latter in the host’s organism.

Another important point in the development of helminthiasis is the functional activity of various populations of T-lymphocytes which is considered to be the basis of the regulation of the immune response. In particular, the activity of T-helper cells 1 (Th1-lymphocytes) contributes to healing from helminthiasis while increased activity of T-helper cells 2 (Th2-cells) worsens the condition of sick animals. Activity of Th2-lymphocytes stimulates antibody formation, including IgA and IgE production, suppresses the parasitocidal action of macrophages and neutrophils and is an alternative to Th1-lymphocytes activity.

In our studies, an increase in the number of B-lymphocytes for the esophagostomiasis of pigs is an indicator of the development of immune protection by humoral type.

Ezofagostomiasis invasion in sows causes changes in the parameters of nonspecific resistance and immune reactivity, which are manifested through leukopenia, neutropenia, eosinophilia, lymphocytopenia, T-cell suppression and activation of the B cellular immunity, as well as through a decrease in phagocytic activity of neutrophils, bactericidal and lysozyme activity of serum which indicates an imbalance in the mechanisms of natural protection caused by the causative agents of esophagostomiasis.

We believe that the study of natural resistance and immune reactivity in esophagostomiasis infested pigs against the background of anti-helminthic therapy with immunomodulatory drugs application is a promising direction for further research.

Key words: esophagostomosis invasion, pig sows, hematological indices, natural resistance, nonspecific resistance, immunological reactivity.