In this study, polyclonal antibodies (pAb) were prepared against Fasciola gigantica excretory/
secretory (E/S) products and purified to demonstrate the highly reactive epitopes on the different
life cycle stages of F. gigantica and on blood cells and different organs of naturally infected
cattle, as well as to screen internal organs for localization of E/S antigens to find out a suitable
method for diagnosing the disease as early as possible. Using anti-F. gigantica E/S IgG pAb,
immunostaining of different life cycle stages of F. gigantica detected strong positive reactions in
all stages except eggs. The reactions were along tegumental surface, gut region of cercariae,
miracidiae, metacercariae and tail of cercariae. Besides, the tegument, spine surface, muscularis
and gut region of the adults were also positive. Immunoperoxidase localization of E/S products
by anti-F. gigantica E/S IgG pAb showed that E/S antigens were located in many organs of
naturally infected cattle. Examination of peripheral blood mononuclear cells (PBMNCs)
represented a high positivity in the phagosomes and activated monocytes as well as in cytoplasm
of lymphocytes. Compared to sections of normal uninfected hosts, liver sections of infected
bovine hosts showed collapsed hepatocytes, thickened portal tract and a highly positive reaction
in the cytoplasm of the liver cells. Target epitopes were located inside the splenic cells, mainly
lymphocytes. In the gall bladder, positive peroxidase reactions were found in the mucosa and
muscularis layers, and in the epithelial cells lining mucosal glands. A marked positivity was in
other organs of the naturally infected animals, as in the epithelial layer lining the glomeruli and
tubules of the kidney, in heart cardiac muscle fibres and in cells lining the alveoli of the lungs.