THEILERIOSES OF CATTLE

J A LAWRENCE - Extraordinary Professor, DPhil, BSc, MRCVS (ret.), DTVM, Department of Paraclinical Veterinary Science, University of Zimbabwe, Harare, Zimbabwe 
M OOSTHUIZEN - Parasitology, PhD, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, Private Bag X04, University of Pretoria, Gauteng, 0110, South Africa
K P SIBEKO-MATJILA - Senior Lecturer, BSc, PhD, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, Private Bag X04, University of Pretoria, Gauteng, 0110, South Africa

Theileria is a genus comprising tick-transmitted parasitic protozoa in the family Theileriidae, order Piroplasmida, subclass Piroplasmia, phylum Apicomplexa. It includes parasites previously allocated to the genera Cytauxzoon, Gonderia and Haematoxenus. The taxonomy of the genus at species level has always been complex. The advent of molecular techniques for characterization has led to the classification of clades and species on the basis of sequence differences in the hyper-variable region of the 18S rRNA gene.  Clades are of interest from an evolutionary aspect but do not always reflect biological similarities. Sequential similarities and differences resolve some uncertainties as to the identity of isolates from different regions and species but give rise to some bizarre anomalies, e.g., the presence of Theileria luwenshuni (a parasite of ungulates) in hedgehogs; this anomaly suggests that either sequencing is not the whole answer to taxonomy, or that there are  aspects of Theileria biology that warrant exploration.

Of the species of Theileria that infect cattle, the most important in sub-Saharan Africa is Theileria parva. Theileria annulata is the only other major cause of bovine theileriosis and occurs in North Africa, southern Europe and Asia. These two species, together with T.taurotragi, owe their pathogenicity to their ability to transform the host cells in which the schizonts develop to multiply and spread without control through the animal body. Theileria buffeli/orientalis has also emerged as an important pathogen in the Orient and Australasia, even though it does not transform host cells.

For the purposes of Anipedia, East Coast fever in its classical form is described as the type example of theilerioses in cattle in southern and eastern Africa. Other diseases caused by members of the T. parva complex are considered in comparison with East Coast fever. Theileria annulata theileriosis is described as a separate entity. Other pathogenic or potentially pathogenic species of Theileria are described separately, and non-pathogenic species whose presence affects the diagnosis and control of the pathogenic species are considered in a single chapter.

Table 1: Theileria species affecting cattle

? unknown