Evaluation of the functional activity of immune responses and physiological parameters of lake frogs Pelophylax ridibundus (Amphibia: Ranidae), infected with blood parasites

We carried out a comparative assessment of the hemoparasitic load, immune system functioning and morphophysiological parameters of males (13 individuals) and females (11 individuals) of lake frogs Pelophylax ridibundus from the Astrakhan region of Russia. In the blood of lake frogs (14 individuals: 9 females and 5 males), hemoparasites belonging to three genera: Dactylosoma, Hepatozoon and Trypanosoma were identified. The most common gamonts were Dactylosoma sp. (in 14 individuals), Hepatozoon sp. were found in 7 individuals, and the extracellular form of Trypanosoma sp. - in 5 individuals. The proportion of infected erythrocytes, the extent of invasion, and the index of abundance of hemoparasites in females were significantly higher than in males. Leukocyte profiles of infected males and females did not differ; intersexual differences were found in healthy individuals. The females had a higher blood cell index and a white blood cell shift index, compared with a lower value of the lymphocyte-granulocyte index. Infected males differed from healthy ones by a low neutrophil nuclear shift due to an increase in segmented neutrophils in the blood. Hemoparasite infestation correlated with a decrease in the total number of erythrocytes, an increase in the proportion of myelocytes, an increase in the body's intoxication index, the level of large immune complexes, and a decrease in the enlargement index (the ratio of large to small immune complexes). Localization of Hepatozoon sp. in erythrocytes correlated with an increase in the index of the heart, liver and gonad of lake frogs. A negative correlation was found between the content of Dactylosoma sp. in erythrocytes and a decrease in the heart index in all infected frogs; as well as between the presence of Trypanosoma sp. in the bloodstream and a decrease in the kidney index. The obtained results illustrate the development of an inflammatory reaction and impaired immunoregulation of the body of lake frogs when infected with hemoparasites.