Trypanosomatids (Kinetoplstea: Trypanosomatida) and insects (Insecta): patterns of co-evolution and diversification of the host–parasite systems

Some of the most dangerous human diseases are caused by various trypanosomatid species: Chagas disease in the South and Central America, African sleeping sickness and cutaneous and visceral leishmaniasis. These diseases are common in hot climates. About three million new cases of trypanosomiasis and leishmaniasis are reported every year. More than a third of the world population lives in the areas with the constant risk of infection. Increased tourist flow and the uncontrolled migration from the southern countries into the temperate regions as well as global climate changes create multiple opportunities for trypanosomatids to spread beyond their traditional areas. Trypanosomatid expansion is only limited by distribution of their insect vectors, since the development of these parasites inside a vertebrate host (including humans) has no latitudinal constraints. In the following chapter we examine specific coevolutionary patterns connecting these parasites and their hosts. How deep are the links between a specific parasite and its host (or hosts)? How and at which levels their interactions are controlled? Is it possible for a parasite to colonise a new host and what are the factors facilitating or limiting such changes? These and similar questions, actively debated in the modern literature, are the main focus of this chapter. Analysis of the abundant, though incomplete and, at times, contradictory, data led us to conclude that the horizontal transition to the new insect vectors is the most important mode of host-parasite systems diversification in trypanosomatid evolution. One may speculate that this group is even now evolutionary active. Trypanosomatids are constantly “experimenting” with the new hosts and, having gained access to the new resources, can expand into new territories. Factors destabilizing the existing host-parasite systems between trypanosomatids and insects may increase the risk associated with these parasites (including the ones infecting humans) expanding from their present areas.