Theileria buffeli⁄orientalis infection

Theileria buffeli/orientalis infection

Previous Authors: J A LAWRENCE

Current Authors:
J A LAWRENCE - Extraordinary Professor, DPhil, BSc, MRCVS (ret.), DTVM, Department of Paraclinical Veterinary Science, University of Zimbabwe, Harare, Zimbabwe  
B J MANS - Principal Researcher, BSc, BSc (Hons) Biochemistry, MSc (Biochemistry), PhD (Biochemistry), Agricultural Research Council, Onderstepoort Veterinary Research, 100 Old Soutpan Road, Pretoria, Gauteng, 0110, South Africa

GENERAL INTRODUCTION: THEILERIOSES OF CATTLE

Introduction

The Theileria buffeli/orientalis group of parasites is widely distributed in cattle around the world. The taxonomy of the group is complex and the nomenclature controversial. The name T. buffeli was given to a parasite recovered from Asiatic buffalo in Indochina by Neveu-Lemaire in 1912, and that of T. orientalis to a parasite recovered from cattle in Siberia by Yakimoff and Soudatschenkoff in 1931.20 The name Theileria sergenti is frequently used to describe a pathogenic member of the T. buffeli/orientalis group that occurs in eastern Asia, but this name is invalid as it had been used previously to describe a parasite of sheep.20 The group also contains other known species such as T. sinensis found in Asia and T. sp. (kudu) found in Africa 16.  Uilenberg proposed in 1985 that the group be named T. orientalis, while later authors proposed T. buffeli, but no consensus has been reached. Both names are used synonymously, depending on the historical background of different scientific groups 16.

The parasites have been described from Asia, Australasia, the Mediterranean basin, Western Europe and North America, although they have often been identified mistakenly as Theileria mutans. Under the name T. orientalis the parasites were first identified in sub-Saharan Africa in Ethiopia in 19832 and they have since been described in central Africa13 and eastern Africa, where they were initially named Theileria sp. (Marula).21 The parasites have also been identified in African buffalo (Syncerus caffer) in South Africa1. In most parts of the world the parasites are usually benign, or cause only mild clinical signs, but in eastern Asia, Australia and New Zealand they may pose an economically significant threat to cattle production.

Sequencing of the 18S rRNA gene has identified 13 different genotypes for the group 5, 16, 17, 18.  A number of major piroplasm surface protein (MPSP) types have been identified, including Buffeli, Chitose, Ikeda and Warwick.   One of these, Ikeda, is responsible for clinical disease in Japan, Australia and New Zealand. In southern Africa the T. buffeli that are found in cattle and buffalo belong to different genotypes, which raises the possibility that they may represent different species 18.

Aetiology, life cycle and epidemiology

The parasites in the T. buffeli/orientalis group normally infect cattle, Asiatic domestic buffalo and African buffalo. Infection in sheep has been detected by molecular methods in China and Vietnam. The morphological and biological characteristics of the group are similar to those of Theileria parva (see East Coast fever: Figure 29.2). Schizonts may be found briefly about 10 days post-infection, and piroplasms appear at the same time.  The macroschizonts are unusually large.29 The piroplasms are often longer than those of other species, and bars are usually found in the erythrocytes associated with the piroplasms; veils are also commonly found with certain isolates, but not with others.13, 21, 29

The main vectors of the group are Haemaphysalis punctata in Europe, the Mediterranean basin and western Asia, H. longicornis, H. japonica and H. concinna in eastern Asia,28 H. humerosa and H. bancrofti in Australia,24 and H. longicornis in Australia and New Zealand.  Peak incidence of infection coincides with peak activity of nymphal and adult ticks in spring and autumn respectively 19.  In Japan, H. longicornis is considered to be the main vector, but the parasite is also transmitted mechanically by sucking lice and tabanid flies. Mechanical transmission with vaccination needles and other agents is possible, but the disease is usually associated with the presence of the vector ticks. The vectors in North America and sub-Saharan Africa have not been identified. No Haemaphysalis ticks occur on cattle in North America, while in Africa the only Haemaphysalis that occurs on cattle as both immatures and adults is H.aciculifer,27 which is not thought to be sufficiently common to act as a vector.2 It has been suggested that H. silacea may be the possible vector of buffalo specific members of this group in South Africa, since it was found to parasitize buffalo in some of the regions where parasites occur 5, 10,18,30Ixodes species are possibly involved, as two species have been identified as potential vectors in Japan. The parasite is readily transmissible between cattle by blood inoculation.29 Transplacental infection does occur in the field at a low rate but is not considered to be a major factor in the epidemiology of the disease 15, 25.

The Theileria buffeli/orientalis group is assumed to be widespread throughout the range of its tick vectors and often occurs in mixed infections with other species of Theileria. It is rarely associated with clinical disease, except in cattle of exotic breeds in eastern Asia and in Australasia, where the Ikeda strain has been incriminated. Benign Theileria buffeli/orientalis

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