Transcriptomic Profiling of Trypanosoma Congolense Mouthpart Parasites from Naturally Infected Flies

Abstract Animal African Trypanosomiasis, or nagana, is veterinary disease caused by African trypanosomes transmitted by tsetse flies. In Sub-Saharan Africa, Trypanosoma congolense is the major cause of nagana in livestock, resulting in high animal morbidity and mortality and extensive production losses. In the tsetse fly, parasites colonise the midgut and eventually reach the mouthparts, from where they can be transmitted as the fly feeds on vertebrate hosts such as cattle. Despite the extreme importance of mouthpart form parasites for disease transmission, very few global expression profile studies have been done in these parasite forms. Here, we collected tsetse flies from the Shimba Hills National Reserve, a wildlife area in southeast Kenya, diagnosed T. congolense infections, sequenced the transcriptomes of the T. congolense parasites colonising the mouthparts of the flies, and compared their expression profiles with those of parasites collected from experimental fly infections. We found little correlation between mouthpart parasites from natural and experimental fly infections. Furthermore, we performed differential gene expression analysis between mouthpart and bloodstream form parasites and identified several surface-expressed genes and 152 novel hypothetical proteins differentially expressed in mouthpart parasites. Finally, we profiled variant antigen expression and discovered a VSG gene constitutively expressed in metacyclic and bloodstream form parasites, that may be subject to novel developmental regulation. Our study is the first to provide trypanosome transcriptomes of parasites from naturally infected tsetse flies and highlights the need to confirm findings from experimental models of infection in epidemiologically-relevant settings.