FINAL DIAGNOSIS - Hepatic coccidiosis

Case History

  This case involved a meat rabbit farm with some 1500 animals.  A female rabbit, approximately 7-11 weeks of age, was presented alive to the Animal Disease Diagnostic Laboratory at PurdueUniversity for euthanasia and necropsy.  The reported history was that the animals are asymptomatic for approximately 5-6 weeks at which time they begin to develop diarrhea.  At this time, the owners also report sudden deaths in many rabbits.

Gross Necropsy Findings:

  The rabbit was thin (weighing 2 pounds, 4 ounces) with reduced fat stores and muscle development.  The hair coat was rough and fecal material was adhered to hair at the perineum.  Small intestinal loops were swollen and gray.  Gray-green, semi-solid digesta filled the small intestines.  Formed fecal pellets were in the colon.  A direct examination of the fecal material revealed numerous oval, colorless, thin-walled oocysts, each with a single, round sporont (morphologically consistent with coccidian oocysts).

Histopathologic Findings:

  Hepatic lobules had extensive biliary hyperplasia with numerous intralesional coccidia.  Bile ducts were markedly dilated and lined by hyperplastic columnar epithelial cells thrown into multiple papillary fronds.  Numerous protozoal developmental stages (including undifferentiated gamonts, micro- and macrogametocytes and developing oocysts) ranging in size from 25-50 microns in diameter were within lining epithelial cells.  Ductal lumens were filled with numerous, thin-walled, approximately 50 microns in length, ovoid oocysts (based on location and morphologic characteristics,  these organisms were consistent with Eimeria stiedae).  The hyperplastic bile ducts were surrounded by large amounts of fibrous connective tissue with lymphohistiocytic inflammatory infiltrates.

Morphologic diagnosis:

  Liver; Marked chronic proliferative cholangitis with intraepithelial coccidial organisms and hepatic atrophy

Etiology:

  Eimeria stiedae

Discussion

  Eimeria species are coccidian parasites of the phylum Apicomplexa.  They are parasites of the epithelial cells of the gut mucosa and those lining certain ducts.  The life cycle of each species is host specific and direct.  Eimeria species can be a serious problem in lagomorphs (especially in the young), where as many as 14 species of coccidian parasites have been described, all but one being found in the small intestine, cecum or colon.  E. stiedae  is an inhabitant of the epithelial cells of the bile ducts and is the cause of severe liver damage in rabbits.  The rabbit is infected by ingestion of sporulated oocysts.  Sporozoites penetrate the mucosa of the small intestine and pass via the hepatic portal system to the liver and the mesenteric lymph nodes.  In the liver, they enter the epithelial cells of the bile duct and occasionally the liver parenchymal cells, where they become schizonts.  The schizonts produce merozoites, but the number of asexual generations is unknown.  Oocysts pass through the bile and appear in the feces 18 days after ingestion; sporulation occurs in 3 days.  Light infections are often inapparent.  Heavy infections are characterized by anorexia, a distended abdomen and weight loss and, occasionally, diarrhea and icterus.  The liver is greatly enlarged, the bile ducts are dilated and appear on the surface of the liver as white nodules of variable size and contain creamy fluid packed with oocysts.  Microscopically, there is destruction and regeneration of the bile ducts epithelium with extensive hyperplasia of the ductular epithelium.  Developmental forms of the parasite are seen in the bile duct epithelial cells and

oocysts appear in the lumen.  Biliary outflow may be obstructed by oocysts, resulting in a distended bile duct.  The liver parenchyma may be destroyed by the pressure from the expanding biliary ducts and gradually replaced by fibrous connective tissue.  A diagnosis of E. stiedae infection can be made by the demonstration of very large numbers of oocysts in the feces, but since intestinal coccidian are frequently present in rabbits and may be present in large numbers without any serious clinical signs, the most significant diagnosis is made by examination of the liver.  Control of infection requires strict attention to sanitation and husbandry.  Avoidance of stress, frequent disinfection of cages, hutches, transport carriers, and litter pans with 10% ammonia solution may reduce or prevent clinical disease.  The most effective chemotherapeutic agents used to treat hepatic and intestinal coccidiosis are the sulfonamides.  Their major role may be to control the organism until natural immunity develops.

 - by Jan Lacey, DVM,

   ADDL Graduate Student