Spontaneous interstitial myocarditis in rabbits.

Abstract

This study began with the observation of myocardial lesions in the hearts of normal rabbits and guinea pigs which served as controls in a series of experiments in which attempts were made to transmit rheumatic fever to laboratory animals.

The rabbits which form the basis of this report were obtained from a variety of sources over a period of 3 1/2 years. They were kept under careful observation for periods varying from a few days to 4 months. None has been included which manifested any clinical sign of disease, such as snuffles, diarrhea, ear canker, loss in weight, cutaneous or subcutaneous infections. They were killed by a blow on the back of the head. A complete autopsy was performed, but only the hearts were prepared for microscopic examination. A number of sections of each heart were examined.

The lesions were somewhat more common in old than in young rabbits. They varied in size from small groups of 6 or 8 cells to large areas the size of a high power field. They consisted of infiltrations between the muscle fibers of lymphocytes and endothelial leucocytes. Some of the lesions, particularly the smaller ones, contained only cells of one type. In others they were mixed in varying proportions, to which were occasionally added small numbers of polymorphonuclear eosinophiles, fibroblasts and plasma cells. The lesions occurred most frequently between the muscle fibers of the papillary muscles and ventricular walls, but occasiona'lly beneath the endocardium and epicardium. None was ever found in the valves or at the bases of the valves. The muscle fibers passing through the lesions occasionally showed loss of striation, but rarely evidence of marked degenerative changes.

Careful search has revealed no bacterial or protozoan microorganisms or cell inclusion bodies.