Potential Vectors of Trypanosoma evansi in Camels in Eastern Chad

Abstract

Eastern Chad is a camel breeding area. Trypanosoma evansi infections (surra), which are mechanically transmitted by various hematophagous biting insects, are widespread in the area. They primarily affect transhumant herds. An entomological survey was carried out in seven representative sites in order to improve the knowledge of the epidemiology of surra in the area. Four sites (Koukou Angarana and Djogori in the South, Oum Chalouba and ouaddi Fira in the North) were associated with a high prevalence of the disease, the other three (Abdi in the South, Am sak and ouaddi Fama in the North) with a low prevalence. The survey was based on the use of 15 biconical traps Challier-Laveissiere and five Nzi traps. Captures were recorded at 24 and 48h. Three series of trappings were performed to take into account seasonal variations. Various factors which could influence captures were included in a multivariate analysis. In total, 1272 Stomoxyinae (stable flies), 945 Tabanidae (horse flies) and 226 hippoboscids were caught. Among horse flies, Atylotus agrestis was the most abundant species; the others were Tabanus gratus, T. taeniola and T. biguttatus. The main three stable flies identified were Stomoxys calcitrans, S. sitiens and S. niger. Most of the hippoboscids identified belonged to the Hippobosca camelina species. The main factors which explained the variability of the captures were the type of trap, the season and the latitude. The Nzi trap was the most efficient trap to catch horse flies and stable flies. The best capture period was at the beginning of the dry season (November to January) for Atylotus agrestis, Stomoxyinae and Hippoboscids. Tabanus gratus was mainly captured at the end of the dry season (February to May) and during the rainy season (June to October), and Tabanus taeniola during the rainy season. The Hippoboscids were more frequently captured in the north of the study area and T. gratus and T. taeniola in the south. A correlation was found with both trap types between the number of biting insects caught during the dry season and surra prevalence. The high prevalence of surra in transhumant herds could be explained by the cumulative effect of cattle in contact with (1) the peak of A. agrestis in the North at the end of the rainy season and at the beginning of the dry season and (2) biting insects present in the transhumant reception zone of the South (November to June). An explanation for the impact of surra on short-distance transhumant and semi-sedentary herds of the North might be found in the nature itself of the area, i.e. whether or not it allows populations of hematophagous insects to be maintained during the dry season.