Overview of the Vectors and Their Role in Transmission of African Animal Trypanosomiasis

Classification

The tsetse flies, Glossina species are of great veterinary and medical importance because they transmit the trypanosome parasites that cause both the human and the animal forms of trypanosomiasis. The taxonomy of Glossina species is well known and any prior controversies about the taxonomic classification are considered resolved (Lane and Crosskey 1993). Tsetse flies belong to the phylum Arthropoda. The major characteristic of Arthropoda is the division of the body into three segments viz. the head, thorax and abdomen. Tsetse flies are further classified into the order Diptera (or “true flies”). Thus, tsetse flies, like other Dipterans, possess a thorax bearing a single pair of functional wings. The second pair of wings has been adapted to form halters, which help the insect to maintain in-flight balance. Under the Order Diptera, tsetse flies are placed within the superfamily Hippoboscoidea due to the morphological and reproductive similarities of tsetse flies to keds and other hippoboscid flies (McAlpine, 1989). The superfamily Hippoboscoidea contains four families including the Hippoboscidae (ked flies) and the Glossinidae, mono-genetic family with only one genus Glossina, wherein the tsetse flies are classified. The genus Glossina is divided into three distinct taxonomic groups (subgenera) based on anatomical characteristics (e.g. external genitalia of the males). The differentiation of the subgenera is also roughly co-related to the environmental territory of the flies. These three groups are the morsitans (savannah-dwelling), palpalis (riverine or lacustrine-dwelling) and the fusca (forest-dwelling group). One of the earliest species-specific descriptions of tsetse flies was given by Westwood in the l800’s. Since then, more than 30 different species and subspecies have been described. The most recent species to be identified and described is Glossina frezili, which infests the mangrove swamps in Congo (Gouteux, 1987). The currently known tsetse fly species and subspecies are detailed in Table 1.