Observations on the pathology of experimental avian spirochaetosis.

In experimental infection of chickens with a virulent strain of Borrelia anserina, peak spirochaetaemia was recorded from 72 to 96 hours. Progressive enlargement of the spleen with mottling was the predominant gross finding. Spleen, liver and small intestine showed extensive erythrophagocytosis, which continued even after the disappearance of spirochaetes from blood and tissues. While haemosiderosis was mild in the lungs, it was absent from the heart, kidney and brain. Spirochaetes were demonstrable in the spleen, liver, intestine, kidney and to a lesser extent in the lungs, but absent from the heart and brain. Widespread erythrophagocytosis and extravascular haemolysis suggest involvement of an immune mechanism in the pathogenesis of splenomegaly.