Introduction

Abstract

Abstract Identification of the infectious organisms and their arthropod vectors are the essential first steps that enable scientists to understand vector-borne diseases, i.e., disease agents that can infect vertebrate animals and (in most cases) humans. Many, perhaps most, vector-borne diseases are zoonoses, i.e., they infect a variety of vertebrates and are also transmissible to man. In the case of tick-borne zoonoses, knowledge of these diseases has accumulated gradually over the preceding 100 years. Smith and Kilbourne’s (1893) report of the transmission of the malaria-like protozoan, Babesia bigemina, by the cattle tick, Boophilus annulatus, began this era of discovery, which has continued throughout the 20th century. Numerous reports of tick transmission of other diseases soon followed: examples include relapsing fever by soft ticks (Dutton and Todd, 1905), East Coast Fever by the African brown ear tick (Rhipicephalus appendiculatus) (Theiler, 1904), Rocky Mountain spotted fever by wood ticks (Dermacentor andersoni) (Ricketts, 1906, 1907), Boutonneuse fever by the brown dog tick (Rhipicephalus sanguineus) (Brumpt, 1932), and babesiosis of cattle, dogs, and other animals by many different tick species (summarized by Kuttler, 1988). The decades since World War II have seen equally dramatic discoveries, including tick transmission of tick-borne encephalitis, Crimean-Congo Hemorrhagic Fever (Chumakov et al., 1968, 1969; Casals, 1969), Kyasanur Forest Disease (Bhat, 1991), Lyme disease (Johnson et al., 1984) and human Ehrlichiosis (Anderson et al., 1991), to name but a few examples. These important discoveries have led to a vast literature dealing with the biology of the pathogenic agent and the pathologic response of the human or animal hosts.