The pathological physiology of heartwater [Cowdria (Rickettsia) ruminantium - Cowdry, 1926]

Abstract

The pathological physiology of heartwater has been studied in acute, untreated fatal cases in sheep and cattle. No significant changes could be found in the blood constituents. The main findings were (a) disappearance of circulating eosinophiles; (b) sympatholysis manifested firstly by a fall in haematocrit readings due to splenic relaxation followed by a subterminal peripheral vaso-collapse with a dramatic fall in arterial diastolic pressure; and (c) a terminal catastrophic drop in plasma volume due to an increased capillary permeability which allows of the passage of plasma proteins from the vascular system. The use of sympathomimetics and intravenous infusions of packed red cells or whole blood are recommended as supportive treatment in advanced cases. The possible practical applications of the finding of the disappearance of the eosinophils prior to the onset of the febrile reaction will be investigated further. Three sheep showing collapse after having received chemotherapy late in the heartwater reaction were studied. These animals were showing general collapse. The condition is described as a functional decerebration with the vegetative functions of the body proceeding more or less normally. The cerebral damage would appear to be irreversible.