Pathology of acute Leptospira interrogans serotype icterohaemorrhagiae infection in the Syrian hamster

The pathology of acute Leptospira interrogans serotype icterohaemorrhagiae infection in the Syrian hamster was investigated up to 7 days after infection using histology, electron microscopy and an indirect fluorescence test for leptospires. The disease was characterized by the presence of many leptospires in the tissues, jaundice, leukocytosis, haemorrhages, endothelial alteration and thrombotic glomerulopathy. The leptospires were present intravascularly, in the interstitium penetrating between liver cells and tubular epithelial cells and in the tubular lumina. The presence of leptospires was not necessarily associated with lesions. These findings support both pathogenetic mechanisms suggested in the literature, namely: the ability of leptospires to penetrate actively between cells with detachment of tight junctions, without obvious lesions to the cells, and an immune-mediated process with immune complex formation and binding and activation of complement resulting in leukocytosis, thrombotic glomerulopathy, endothelial alteration and haemorrhages.