Triclabendazole is the drug of choice against Fasciola spp. infections in humans and animals. However, parasitic resistance against triclabendazole is spreading in the veterinary field. The objective of this study was to assess of flukicide efficacy of triclabendazole through evaluation of the histopathology of Fasciola hepatica adult fluke’s specimens. For this, the efficacy test was performed on naturally infected sheep treated with triclabendazole (Fazinex®) at the dose recommended for F. hepatica, in which the flukes recovered at necropsy on the 7th day post-treatment and separated for histological examination. The teguments and intestines from F. hepatica recovered from treated and control sheep were examined by microscopy. In the outer and inner parts of the tegument, edema and swelling of its structural components are noted. The spines in the tegument were enlarged, swollen, take on a more rounded shape and have changes in color, perceiving the eosinophilic dye in greater concentration. There was a detachment of the brush border of the intestinal epithelium and the accumulation of microvilli of the apical part of the epithelium in the intestinal lumen. The cellular structures of the intestinal epithelium were melted. The results indicated that the teguments and intestines of F. hepatica were severely affected by triclabendazole and demonstrated the importance of the use of histopathology for the diagnosis of therapeutic efficacy in field strains.

General characteristic of parasitologic situation at the exclusion zone, some aspects of new conditions influence on separate systematic groups of mammal parasites Polesye State Radiation and Nature Reserve of the Republic of Belarus were presented. Research of helminth fauna and helminthological situation was realized by an example of 1 European bison, 7 mooses, 20 roe deers, 26 boars, 25 wolves, 50 racoon dogs, 6 foxes and 3 beavers. Scatoscopy of the animal excrements was realized by Kalantaryan method with saturated solution of sodium saltpeter, Berman method. Research results revealed 66 helminth species belonging to 4 classes and 34 families. There were found 10 parasite species at bison, 16 – at mosses, 17 – at roe deers, 16 – at boars, 8 – at deers, 23 – at wolves, 13 – at raccoon dogs, 13 – at foxes, 9 – at badgers and 1 – at beavers. Analyze of helminthofauna of the analyzed area showed that the nature reserve had its own helminthes complex. A lot of stated helminth species were parasites with a wide range of hosts, including domestic animals, and cattle. Wolves, foxes and raccoon dogs were hosts of some custodies invasions. Carnivorous animals and murine rodents were hosts of trichinosis invasion, which was stated at 41,2 % of raccoon dogs, 33,3 % of foxes and 16,7 % of wolves. Also trichinas were stated at bank vole (1,3%), yellow-necked mouse (2,7%), and house mouse (16,6%)