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INTRODUCTION
Ticks transmit a greater variety of pathogenic micro-organisms, protozoa, rickettsiae, spirochaetes and viruses, than any other arthropod vector group, and are among the most important vectors of diseases affecting livestock, humans and companion animals. Moreover, ticks can cause severe toxic conditions such as paralysis and toxicosis, irritation and allergy. This chapter discusses the global importance of ticks and tick-borne diseases.
Whereas the importance of tick-borne diseases for humans and companion animals is measured by morbidity and mortality, the diseases transmitted by ticks to livestock are an additional major constraint to animal production predominantly in (sub)tropical areas of the world. In general, tick-borne protozoan diseases (e.g. theilerioses and babesioses) and rickettsial diseases (e.g. anaplasmoses and heartwater or cowdriosis) are pre-eminent health and management problems of cattle and small ruminants, as well as buffalo, affecting the livelihood of farming communities in Africa, Asia and Latin America. Recently, tick-borne diseases were again ranked high in terms of their impact on the livelihood of resource-poor farming communities in developing countries (Perry et al . 2002; Minjauw & McLeod, 2003). This is particularly relevant in parts of sub-Saharan Africa, Asia and Latin America where the demand for livestock products is increasing rapidly (Delgado et al . 1999).
Ticks and tick-transmitted infections have co-evolved with various wild animal hosts which often live in a state of equilibrium with them and constitute reservoir hosts for ticks and tick-borne pathogens of livestock, pets and humans. They have only become problems of domestic livestock when these wild hosts came into contact with them, either because man moved livestock into infested regions, or moved livestock infested with the ticks into previously uninfested regions. An example of man moving livestock into infested regions is the introduction of cattle into Africa where they came into contact with Rhipicephalus appendiculatus , the vector of Theileria parva , the causal agent of East Coast fever and related diseases; the African buffalo is the normal host of T. parva and the infection is normally subclinical in this animal. An example of man moving ticks and tick-borne diseases with livestock is the introduction of Boophilus ticks together with the livestock diseases they transmit into the American continent.
Whereas the global economic importance of ticks is particularly high for livestock, there...