Eperythrozoon ovis infection of sheep

Abstract

Eperythrozoon ovis is a bacterium usually associated with subclinical disease in sheep but occasionally resulting in anaemia and death. Two one-year-old tups presented with pale mucous membranes, skin lesions and swollen joints, andE. ovis was identified from blood samples. In spite of treatment, one tup died and at post-mortem examination showed evidence of haemosiderin deposits in the kidneys. The other tup failed to clear the parasitaemia but showed an improvement in red blood cell parameters following prolonged tetracycline therapy. A possible mechanism of persistence ofE. ovis infection in this tup was investigated by isolating and quantitying lymphocyte and lymphocyte subset numbers from peripheral blood, as deficits in these have been associated with disease in a number of different species where suppression of immune responses is a feature. When compared to control sheep, the survivingE. ovis-infected tup was shown to have a decrease in T lymphocytes expressing the CD2 and CD4 molecules, whereas T lymphocytes expressing the CD8 molecule and B lymphocyte numbers were unaffected. The reduction in T lymphocytes expressing CD4 molecules and the resulting reversal of CD4:CD8 ratios in this tup is similar to that seen in human and feline immunodeficiency virus infections, although an ovine immunodeficiency virus has not, to date, been recognised.