Pathology of Experimental Sarcocystis falcatula Infections of Canaries (Serinus canarius) and Pigeons (Columba livia)

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Abstract
Sarcocystis falcatula is an apicomplexan parasite with a broad range of avian intermediate hosts. The pathology and pathogenesis of infection with this parasite has been studied experimentally in the budgerigar (Melopsittacus undulatus). The present study quantitatively examines the pathology of this parasite in canaries (Serinus canarius) and pigeons (Columba livia) and compares it with that found in budgerigars. The general progression of merogony and cyst formation is similar qualitatively to that seen in budgerigars, but it differs quantitatively. The principal site of precystic merogony is in pulmonary endothelial cells. The magnitude of pulmonary meront burdens (at similar inoculated dosages) varies in different intermediate host species. Merogeny is less persistent than in budgerigars. Among the various species of birds, the magnitude of precystic merogony correlates differently with the magnitude of skeletal muscle cyst burdens. The distribution of cyst burdens among various muscles also differs. The composition of inflammatory cells differs among various avian species'' response to S. falcatula. Pathologic changes quantitatively parallel tissue meront burdens (except possibly in the liver of canaries), resulting in an interstitial pneumonitis, hepatitis, and mild inflammatory lesions of other organs.