Genetic engineering of Trypanosoma (Dutonella) vivax and in vitro differentiation under axenic conditions.

Trypanosoma vivax is one of the most common parasites responsible for animal trypanosomosis, and although this disease is widespread in Africa and Latin America, very few studies have been conducted on the parasite's biology. This is in part due to the fact that no reproducible experimental methods had been developed to maintain the different evolutive forms of this trypanosome under laboratory conditions. Appropriate protocols were developed in the 1990s for the axenic maintenance of three major animal Trypanosoma species: T. b. brucei, T. congolense and T. vivax. These pioneer studies rapidly led to the successful genetic manipulation of T. b. brucei and T. congolense. Advances were made in the understanding of these parasites' biology and virulence, and new drug targets were identified. By contrast, challenging in vitro conditions have been developed for T. vivax in the past, and this per se has contributed to defer both its genetic manipulation and subsequent gene function studies. Here we report on the optimization of non-infective T. vivax epimastigote axenic cultures and on the process of parasite in vitro differentiation into metacyclic infective forms. We have also constructed the first T. vivax specific expression vector that drives constitutive expression of the luciferase reporter gene. This vector was then used to establish and optimize epimastigote transfection. We then developed highly reproducible conditions that can be used to obtain and select stably transfected mutants that continue metacyclogenesis and are infectious in immunocompetent rodents.