Fatal theileriosis in eland (Taurotragus oryx): pathology of natural and experimental cases.

Clinical, parasitological and pathological studies were made on five eland infected with Theileria. Three were natural Theileria infections while the other two were experimental cases. All eland died. Generalised lymph node enlargement was a common feature. Wasting occurred in the more prolonged cases and in two of the field cases severe terminal diarrhoea developed. The third field case died in severe respiratory distress. In all cases, up to 50 per cent piroplasm parasitaemia was wound and schizonts were seen in lymph node biopsy samples and in lymphoid smears prepared at necropsy. These parasites showed the morphological characteristics of Theileria taurotragi. The cells parasitised by schizonts had the morphological features of large lymphoid cells. These were infiltrated widely throughout the tissues and organs examined including the lymphoid organs, the gastrointestinal tract (in two cases this was the cause of death), adrenal glands, liver, lungs and to a lesser extent the heart and kidneys. In the one case in which the brain was examined, it was found to be involved. The severely affected organs were diffusely infiltrated with parasitised cells both intravascularly and extravascularly. Lymphocytolysis, necrosis, thrombosis and haemorrhage were frequently encountered in association with parasitised cells. All eland involved except one were males despite the fact that there were more females in the herds.