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Red Deer (Cervus elaphus) are not a perfect host for Fascioloides magna : evidence from a histopathological study

Fascioloides magna is one of the most important parasites of a variety of wild ruminants in North America and Europe. The only indigenous primary definitive host of F. magna is white-tailed deer (Odocelius virginianus) where fluke are encapsulated in thin-walled fibrous capsules and eggs passed out through the bile system. Common definitive hosts are other cervids including Cervus alaphus canadensis, Rangifer tarandus, Cevus elaphus, Dama dama and Capreolus capreolus. In dead end host, such as large bovines, llamas and horses infection is characterized by excessive fibrosis, thick-walled encapsulation and black pigmentation. In this study samples of 30 livers infected with F. magna were analyzed histopathologically in order to evaluate the interaction between parasite and red deer (Cervus elaphus). The main histopathological finding is replacement of hepatic tissues with fibrovascular proliferations. They form bridging portal and linear parenchymal fibrosis associated with migratory tracts, concentric hepatic fibrosis around necrotic areas or around flukes forming cyst walls. Iron-porphyrin depositions (parasite hematin) were present inside macrophages trapped within collagen in chronic lesions. This extracellular black pigment was also evident mixed with necrotic debris or within lymph vessels and biliary ducts. Disruption of liver parenchyma resulted with impairment of normal liver blood drainage resulting in arterial smooth muscles hypertrophy and dilatation of central veins, lymph vessels and sinusoids. Acute destructions of parenchyma were characterized with hemorrhage and eosinophylic hepatitis. One of the most common findings in chronic lesions was linear or perivascular inflammatory cell infiltrations of plasma cells and scattered eosinophyls. Multinucleated giant cells of foreign body type were present around dead fluke adults or within cyst walls. Biliary ducts were lined with hyperplastic epithelia containing bile, iron-porphyrin, trematode eggs, and adult flukes in rare cases. High numbers of trematode eggs were found trapped in connective tissue of cyst walls, migratory tracts and especially within granulomas. Most histopathological lesions found in this study suggest that Cervus elaphus develops lesions which resemble bovine lesions. This observation was also supported by the absence of eggs in fecal samples in 40% of animals.

histopathology; Red deer (Cervus Elaphus); Fascioloides Magna

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