Eperythrozoon ovis infection of sheep

Eperythrozoon ovis is a bacterium usually associated with subclinical disea se in sheep but occasionally resulting in anaemia and death. Two one-year-o ld tups presented with pale mucous membranes, skin lesions and swollen join ts, and E, ovis was identified from blood samples. In spite of treatment, o ne 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 tet racycline therapy. A possible mechanism of persistence of E. ovis infection in this tup was investigated by isolating and quantifying lymphocyte and l ymphocyte subset numbers from peripheral blood, as deficits in these have b een associated with disease in a number of different species where suppress ion of immune responses is a feature. When compared to control sheep, the s urviving E, 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 immunodefici ency virus infections, although an ovine immunodeficiency virus has not, to date,been recognised.