Slippery customers: How African trypanosomes evade mammalian defences

African trypanosomes are excellent parasites and can maintain an infection of a large mammalian host for months or years. In endemic areas, Human African Trypanosomiasis, also called sleeping sickness, has been largely unaffected by the advent of modern medicine, and trypanosomiasis of domestic livestock is a major restraint on productivity in endemic areas and is arguably the major contributor to the institutionalized poverty in much of rural sub-Saharan Africa1,2. A simple way of visualizing the effect of the livestock disease is to compare maps showing the distribution of livestock (www.ilri.org/InfoServ/Webpub/Fulldocs/Mappoverty/index.htm) and tsetse flies, the insect vector (www.fao.org/ag/AGAinfo/programmes/en/paat/maps.html): the lack of overlap is remarkable. Tsetse flies are only present in sub-Saharan Africa, and this probably restricted the spread of African trypanosomiasis until historical times. Livestock infections are now present in much of South Asia and South America, a product of long distance trade and adaptation of the trypanosomes to mechanical transmission3. The majority of research is on Trypanosoma brucei as this includes the human infective subspecies. This article provides a description of progress in the understanding the molecular details of how the trypanosome interacts with the mammalian immune system and how these studies have extended beyond this to fundamental aspects of eukaryotic cell biology.