Pathology and pathogenesis of disseminated visceral coccidiosis in cranes.

Disseminated visceral coccidiosis (DVC) caused by Eimeria spp. was recognized as a disease entity in captive sandhill cranes (Grus canadensis) and whooping cranes (Grus americana) in the late 1970s. While most avian species of Eimeria inhabit the intestinal tract of its host, the crane eimerians, Eimeria reichenowi and Eimeria gruis, invade and multiply systemically and complete their development in both digestive and respiratory tracts. In DVC, cranes, especially chicks, may succumb to acute infections resulting in hepatitis, bronchopneumonia, myocarditis, splenitis, and enteritis. Cranes may also develop chronic, subclinical infections characterized by granulomatous nodules in various organs and tissues. This paper reviews the pathology and pathogenicity of natural and experimental DVC in sandhill and whooping cranes. Naturally infected birds appeared clinically normal, but progressive weakness, emaciation, greenish diarrhea, and recumbency before death were observed in birds administered doses > or = 10 x 10(3) sporulated oocysts per os. At necropsy, naturally infected birds had nodules in the mucosa of the oral cavity and the esophagus, and in thoracic and abdominal viscera. Experimentally infected birds necropsied less than 7 days after infection (a.i.) had no gross lesions. Birds examined later had hepatosplenomegaly, liver mottling, lung congestion and consolidation with frothy fluid in airways, and turgid intestinal tracts with hyperemic mucosa. From 28 days a.i., grossly visible granulomatous nodules were seen in the esophagus, heart, liver, cloaca, and eyelids. By light microscopy, the basic host response was a granulomatous inflammation with non-suppurative vasculitis affecting many organs and tissues. With time, multifocal aggregates of mononuclear cells, many laden with asexual coccidial stages, increased in size and number. Widespread merogony resulted in morbidity and death, particularly in birds administered 20 x 10(3) sporulated oocysts. Ultrastructural examination revealed developing asexual coccidian stages in the cytoplasm of large lymphocytes or monocytes within a parasitophorous vacuole, often indenting the nucleus. Oocysts and gametocytes were found in the intestines by 12 days a.i., and in the esophagus, trachea, bronchi, and lung by 14 days a.i., indicating that crane eimerians can complete their life cycle at these sites. Thus, DVC in cranes could be a useful animal model for the study of eimerian extra-intestinal stages and the evaluation of potential systemic anticoccidial drugs.