Clinicopathological Responses to Experimental Infection with Ehrlichia ruminantium in Desert Goat Kids

Abstract

Heartwater (cowdriosis) is a rickettsial infection caused by Ehrlichia ruminantium, affecting wild and domestic ruminants and is transmitted by ticks of the genus Amblyomma. The present study was conducted to investigate the clinical and pathological responses following experimental infection of desert kids with Ehrlichia ruminantium. Experimental kids were allotted into three groups according to their average body weights. The first group (n = 4) served as uninfected control. The second group (n = 4) was injected intravenously with 5 ml of blood collected from the donor goat infected with E. ruminantium to represent a low dose (Ld) of infection. The third group (n = 5) was injected with 7 ml of blood from the infected donor goat with E. ruminantium to represent the high dose (Hd) of infection. The experiment extended for aperiod of 36 days. The infected animals demonstrated the susceptibility of Desert kids to different levels of infective dose. Clinical signs were manifested by fluctuated fever, followed by inappetence, depression, mild incoordination and respiratory distress and death. Pathological alterations in Ehrlichia-infected animals were mainly reflected in the form of moderate effusion of body cavities, hydrothorax and hydropericardium, Flabbiness and congestion of heart muscles were reported. The lungs and brain were congested and oedematous. Crushed smears made from brain cortex showed presence of E. ruminantium colonies. Other lesions included oedema of the mediastinum and associated lymph nodes. The histopathological changes in various organs of E. ruminantium infected goats were similar. The heart showed congestion of blood vessels. Muscle cells appeared thin with a focal proliferation of lymphocytes. The lungs showed areas of collapse, focal oedema, emphysema, haemorrhage and massive congestion of blood vessels and capillaries. A mild to moderate brain oedema, foci of necrosis and perivascular spaces were seen, the kidney showed Moderate dilatation of proximal, distal and collecting tubules were observed and Glomerullar tuft appeared lobulated with widened Boman’s space. The spleen showed prominent white pulp with germinal centres and marked congestion