Trypanosoma vivax: mechanical transmission in cattle by one of the most common African tabanids, Atylotus agrestis

The role of mechanical vectors in the transmission of African livestock trypanosomes has always been controversial relative to tsetse flies, their cyclical vectors. An experiment was carried out in Burkina Faso to demonstrate mechanical transmission of Trypanosoma vivax by one of the most common tabanids in Africa: Atylotus agrestis. Eight heifers (crossbred zebu x Baoule), free of trypanosome infection, were kept in a corral covered by a mosquito net, together with two heifers infected experimentally with a local stock of T vivax. On average, 324 A. agrestis, freshly captured with Nzi traps, were introduced daily over 20 days. Parasitological, PCR and serological examinations were carried out regularly to assess infections and levels of parasitaemia. Microscopic examination of buffy-coats indicated that five of the eight receiver-heifers were infected on days 8, 13, 32, 41, and 48. PCR results indicated that these five heifers were already infected by day 13. Mechanical transmission of T vivax by A. agrestis was demonstrated unequivocally, at a high rate (63% in 13-20 days). Conditions of transmission in this experiment are discussed in terms of natural rates of challenge. The importance of tabanids as mechanical vectors of T vivax should be re-considered, in light of these results. Creation of tsetse free zones in Africa will generally lead to the disappearance of T congolense, T brucei, and most often T vivax as well; however, in areas where T vivax can be mechanically transmitted, clearance of tsetse may not be sufficient to eradicate livestock trypanosomosis. (C) 2003 Elsevier Science (USA). All rights reserved.