A discussion on the classification of the Theileridae

Abstract

The morphological similarity between the members of the genera Theileria and Gonderia in domestic animals makes their differentiation extremely difficult. In making a differential diagnosis veterinarians and zoologists often are compelled to take the pathogenicity and the epizootology into consideration. In doubtful cases it may even be necessary to resort to in vivo cross-immunity tests before a final identification can be made. From this it becomes evident that a great deal of work will have to be done before the "intermediate stages" of the Theileria spp. referred to by Du Toit (1930) can be identified. From the observations on the artificial transmission of East Coast fever (Theiler, 1912; Theiler and Du Toit, 1929) and of Tzaneen disease (Gonderia mutans infection) (De Kock, Van Heerden, Du Toit and Neitz, 1937) it becomes apparent that the infectious agents cannot be maintained by serial passages as has been possible in the case of Gonderia annulata (Sergent, Donatien, Parrot and Lestoquard, 1945). The opinion is expressed that the undetermined species referred to by Du Toit (1930) may behave in a similar way. For systematic studies, therefore, it will be necessary to determine the vectors of these parasites. From this it is obvious that many years will elapse before the classification of this group of micro-organisms can be placed on a permanent basis.