Vascular damage in acute experimental leptospirosis of the guinea-pig.

The pathogenesis of the haemorrhagic diathesis in experimental leptospirosis of the guinea-pig was investigated in the lung, diaphragm and kidney. The vascular damage was found to be focal and mainly capillary. Swollen endothelium with dilated endoplasmic reticulum, enlarged mitochondriae and open junctions seemed to be the initial lesions and endothelial necrosis the final picture in all tissues. The lung capillaries showed endothelial and epithelial blebs and desquamation with many myelin figures. Capillary thrombosis was observed in the pulmonary microcirculation, probably acting as an aggravating factor and being partly responsible for the particularly impressive lung haemorrhages. The peritubular renal capillaries as well as open junctions and gaps due to necrosis also had enlarged fenestrae which were permeable to colloidal carbon particles. The paucity of micro-organisms in the vicinity of the lesions is in accordance with the toxic genesis postulated for the vascular damage in leptospirosis. It is suggested that the vascular lesions induced by leptospirosis begin with increased permeability prior to endothelial necrosis.