Chapter 3 The Enemy Within

Tsetse flies (Diptera: Glossinidae) are vectors of several species of African trypanosomes pathogenic to both man and his domesticated animals. The diseases they cause continue to have a devastating impact at the level of individual lives and the development of the entire African continent. Understanding the key molecular interactions between the trypanosome parasite and its tsetse fly host may enable more effective control strategies. We are now entering a new, exciting phase for such studies because four key trypanosome genomes are in the final stages of sequencing, assembly and annotation, the tsetse symbiont genomes are available and the Glossina genome is in the latter stages of sequencing. To exploit this information to its fullest extent it is essential that all groups of researchers, those studying trypanosomes, the symbionts and those studying tsetse flies, fully understand the biology of all component parts of the interaction. In addition there are very few entomology laboratories working in this area and more need to be recruited if discovery is to proceed at a good pace. To help achieve both aims, we here outline tsetse–trypanosome interactions from an entomological viewpoint. The trypanosome parasite faces a number of barriers to establishment, survival and maturation within the fly host. In particular, we describe how the tsetse midgut environment, the fly immune system and the fly's symbiotic bacteria contribute to these barriers.