Ultrastructure of brain microvasculature in goats with experimental Cowdria ruminantium infection

Abstract

To study microvascular brain lesions in heartwater, 14 Tanzanian blended goats were infected by IV inoculation with the Ball-3 strain of Cowdria ruminantium, monitored clinically during the incubation and febrile periods and killed when temperatures started to drop. Five, clinically healthy goats were used to establish the optimal procedure for perfusion fixation of brains and serve as control. Perfusion was done through the carotid artery under general pentobarbitone anesthesis using 3 % glutaraldehyde at pH 7.4 and 500 mOsm. Samples of brain tissue were collected for light and electron microscopy, complete necropsis were performed and various other tissues taken for light microscopy. Variable signs of CNS disorder and mild hydropercardium developed in all infected goats. Two, essentially different, neuropathologic changes were observed : colonies of Cowdria organisms in endothelial cells of otherwise unaltered vessels and small, perivascular mononuclear cell infiltrations. No signs of vasculitis or abnormal vascular permeability were found. Several perivascular phagocytes contained unusual cytoplasmic inclusions presenting as aggregations of irregularly rounded, membrane-bound particles, 025-04 µm in diameter, in some cases with an internal structure reminiscent of party degraded mitochondris. However, the aggregations Were not convincingly enclosed within membranes as expected in case of autophagocytosis. Another, hypothetical, interpretation is that they represent abortive stages of C. ruminantium attempting to develop extravascularly and that possibly a cell-mediated immune response, developed during and after the incubation period, limits this second cycle within the host and results in the perivascular mononuclear cell infiltrations observed.