Bovine cerebral theileriosis: Histological and ultrastructural investigations

Abstract

Bovine cerebral theileriosis (BCT), or turning sickness is a clinical presentation of parasitic infections of cattle, caused by Theileria spp., that occurs sporadically in South Africa, Burundi, Uganda, Kenya and Tanzania. Clinical signs include circling, blindness, ataxia, opisthotonus and paralysis. The disease can be acute, subacute or chronic, and mainly affects animals between 3 and 5 years old. It is characterised by intense congestion and haemorrhages in the meninges and brain, encephalomalacia, and accumulation of parasitised lymphoblasts in cerebral blood vessels. Macroscopic, histological and ultrastructural lesions observed in 30 indigenous short-horn Zebu cattle from Northern Tanzania, aged 2–9-years-old, which presented characteristic neurological signs of a disease named “Ormilo” by local Maasai herders, were described. Brain smears, prepared from cerebral vessels and stained with Giemsa, revealed extensive lymphocytic infiltration associated with numerous schizonts. Histologically, areas of congestion and haemorrhage associated with obstruction of cerebral vessels with large numbers of parasitised lymphoblasts were the main lesions. Ultrastructural investigations demonstrated the presence of parasites morphologically comparable to flagellated protozoa inside lymphoid cells. This has never been described before in the end host (cattle), but only during the sexual stages within the gastrointestinal tract of ticks. PCR results showed positivity for Theileria taurotragi in 13 samples, suggesting that the parasite could be involved in the aetiology of Ormilo. The alternative hypothesis is that the parasite belongs to a different unknown protozoal genus, having an intra-lymphocytic phase, and being associated with infestation with Theileria spp. Further studies are needed to better understand the morphology of the parasite, its role in BCT, and its potential pathogenic importance for animals.