CEREBROSPINAL LESIONS RESULTING FROM INVASION OF CANINE HEARTWORM LARVAE

In two cases of canine filariasis submitted to necropsy, a large number of worms ofDirofilaria immitis were found in the heart and pulmonary artery, although no neur-ological manifestations had been noticed during life time. Histological examinationrevealed, however, disseminated perivascular lesions resulting from the invasion ofheartworm larvae in the brain and spinal cord of them. Histopathological findings inthe central nervous system were as follows: (a) perivascular cell accumulations situatedprincipally in the Virchow-Robin space and (b) nodular cell accumulations, developedfrom the former, with tissue destruction in the neighborhood of the nodules.Chief elements forminag the cell accumulations were plasma cells and adventitial cells.Lesion (b) was probably caused by tissue desolation due to the mechanical or toxiceffect of larvae penetrating into the parenchyma and passing across the blood vessels, orby tissue reaction to toxic substances which had been produced by the degeuteration ordestruction of larvae penetrating into the parenchyma and acting as foreign bodies.Such nodular lesions may also be regarded as an evidence of the tissue reaction to thedestruction products of the nervous parenchyma. Lesion (a) was thought to be reactionto the inflow of toxic substances derived from immigrating larvae, into the lymphaticspaces, or to the exudation of toxic substances derived froxn mature parasites or toxicproducts produced by the former passing through the weakeuaed wall of blood vessels.In histopathogenesis of perivascular lesions, it should be taken into considerationthat edematous loosening in the wall of blood vessels of small diameter (weakness ofthe wall of blood vessels) is regarded as one of the favoring factors to allow the larvae totraverse blood vessels easily.As causes for weakness of the wall of the blood vessel may be considered the effectsof toxic substances and their products derived from the larva or mature parasite and themechanical effect of the larva. In addition, general nutritional di