Tissue from yearling cattle (Bos taurus),breed and sex unknown.Several livers were collected at slaughter from animals belonging to a single producer, and were submitted
for diagnosis. The veterinarian reported that the animals had been given anthelminthics, which did not appear to be
effective. There was further indication that these lesions had been seen in a few calves the previous year, but that
more animals were affected this year.
Gross findings included the presence of multiple black, irregularly sized tracts throughout the
parenchyma that occasionally contained trematode parasites. Fibrosis was apparent in a minority of lesions.
Liver: There is some variation between slides, with some containing more acute and
others more chronic lesions. However, they are characterized by periportal fibrosis and inflammation together with
much larger randomly distributed tracts that may contain mixed inflammation and hemorrhage, or inflammation and
fibrosis. Eosinophils, plasma cells and lymphocytes dominate periportal infiltrates with more numerous
macrophages, eosinophils and a few neutrophils in migratory tracts. Many macrophages contain small, isomorphic,
birefringent granules of brown cytoplasmic pigment.
Acutely, hemorrhage and eosinophils predominate. Stranded in the fibrosis of chronic lesions or in hemorrhage in acute lesions are scattered operculate ova, each with a well defined yellow-brown shell and a central developing embryo. Some ova are degenerate, with neutrophils or multinucleate phagocytes occur around them. Adult trematodes are present in acute migratory tracts surrounded by hemorrhage, and are not located in bile ducts. They are characterized by an external tegument and absence of a body cavity. Muscular, external suckers are present in some sections. The body is filled by loose, pale eosinophilic parenchyma and suspended within is the intestinal tract, containing brown pigment like that seen in tissue. Vitelline bodies are also sometimes apparent. Both male are female reproductive organs can be seen in some sections. A mixture of eosinophils and lymphocytes is present in peripheral hemorrhage and in the adventitia of portal triads. In areas of acute migration, hepatocytes have undergone localized necrosis without reference of their position in the lobule. Most inflamed portal areas contain increased bile duct profiles.
Acute to chronic multifocal hepatitis, eosinophilic to granulomatous, with
hemorrhage,fibrosis pigment deposition, adult trematodes, trematode ova, and eosinophilic cholangitis with bile duct
Parasites were identified by a veterinary parasitologist as Fascioloides magna.
Fascioloides magna is the liver fluke of white tailed deer and undergoes aberrant
migration in domestic ruminants. In cattle, adults are eventually encapsulated in fibrous tissue and cease migration
at that time, but in small ruminants they continue to wander, causing extensive damage and eventual death(1, 4) In
cattle, cysts containing the parasite do not communicate with the biliary system and ova have no access to feces;
hence the life cycle is incomplete. The black pigment associated with migratory tracts is iron-porphyrin.
Other species are occasionally infected with Fascioloides magna. A single case has been reported in a horse(2) and it
of increasing concern to European farmed cervids, particularly red and fallow deer.(3) Because of the need of a snail
intermediate, Fascioloides magna is not commonly observed in Missouri, although two summers of heavy rain has
probably increased a normally low level of parasitism on certain farms.
Liver: Necrosis and hemorrhage, focally extensive, with adult trematodes, granulomatous hepatitis,
and eosinophilic portal hepatitis and cholangitis.
As the contributor mentioned, there is marked variation between sections, with some
characterized primarily by acute necrosis and hemorrhage associated with adult trematodes, and others with fibrosis
from chronic migration tracts.
A primary differential in this case is Fasciola hepatica, which can be as large as F. magna and may appear similar histologically. In cattle, these two flukes can be differentiated, though, by the location of the adult flukes the liver and the presence of considerable iron porphyrin pigment in Fascioloides magna infections. Adults of F. hepatica are present in bile ducts, while F. magna adults are distributed throughout the liver parenchyma. The migration tracts produced by larval F. hepatica do not generally cause sufficient damage to alter liver function in the host, as may be the case with F. magna. However, clinically important disease can be caused by F. hepatica in cattle and sheep when migrating larvae produce areas of local coagulative necrosis and lower hepatic oxygen tension. The areas of hypoxia create a favorable environment for the germination of Clostridium noyvi spores, resulting in a form of necrotizing hepatitis known as black disease. C. noyvi releases an alpha toxin and the necrotizing and hemolytic beta toxin, lecithinase. In Western and Eastern Europe, black disease may be incited by Dicrocoelium dendriticum. Bacillary hemoglobinuria, caused be the closely related C. haemolyticum, may also occur secondary to F. hepatica migration and has a similar pathogenesis to that of black disease(4).
When Fascioloides magna encysts in the liver, the resulting 2-5 cm diameter encapsulated, pigmented cysts may grossly resemble melanocytic tumors.
1 Cullen JM: Liver, biliary system and exocrine pancreas. In Pathologic Basis of Veterinary Disease, ed. McGavin
MD, Zachary, JF,4th ed., p437. Mosby Elsevier, St. Louis, MO, 2007.
2 McClanahan SL, Stromberg BE, Hayden DW: Natural infection of a horse with Fascioloides magna. J Vet Diagn Invest 17:382-385,2005.
3 Novobilsky A,Horackova E, Hirtova L, et al: The giant liver fluke Fascioloides magna (Bassi 1875) in cervids in the Czech republic and potential of its spreading into Germany. Parasitol Res 100:549-553, 2007.
4 Stalker MJ, Hayes MA: Liver and biliary system. In Jubb, Kennedy and Palmers Pathology of Domestic Animals, ed. M.G. Maxie, 5th, ed., vol. 2, p354-362. Sanders Elsevier, St. Louis MO, 2007.