Hypereosinophilia in rats with Trichinella spiralis infections.

Six LOU strain rats developed blood eosinophil counts of over 10 × 109/1. Six months previously they had been infected with 2 larvae/g of Trichinella spiralis, 2 days after being exposed to high ambient temperatures. The morphology of dividing and peripheral eosinophils was normal, but eosinophils in the blood and peritoneum had increased binding capacity for complexed IgG. Detailed studies were done on 2 rats with blood eosinophil counts of 24 and 32·5 × 109/1. Their hearts were firm and contained adherent thrombus in both ventricles, but there were no histological signs of endomyocardial damage. There were extensive eosinophil infiltrates in lymphoid organs and lungs, and one of the rats had hepatic cirrhosis. Attempts to transfer the disease to syngeneic rats with tissues from affected rats, and to reproduce the disorder in other rats were unsuccessful. The ability of LOU strain rats to expel adult T. spiralis worms, and their eosinophil response in the early stages of infection were normal. It is concluded that hypereosinophilia can sometimes occur in rats, and that this has some features which are also found in hypereosinophilic syndromes of man. It is suggested that the rats with hypereosinophilia had developed the disease as an unusual response to T. spiralis infection. Although the disorder has not been reproduced in other experiments, these findings are described in order to show that they can occur, as the development of an animal model of the hypereosinophilic state would be of value in the study of how the eosinophil response is regulated, and the mechanism of tissue damage that may be seen in association with persistently raised blood eosinophil counts.