Trypanosoma brucei gambiense group 2 experimental in vivo life cycle: from procyclic to bloodstream form.

Trypanosoma brucei gambiense (Tbg) group 2 is a subgroup of trypanosomes able to infect humans in West and Central Africa. Unlike other agents causing sleeping sickness such as Tbg group 1 and Trypanosoma brucei rhodesiense, Tbg2 lacks the typical molecular markers associated with resistance to human serum. Only thirty-six strains of Tbg2 have been documented, and therefore, very limited research has been conducted despite its zoonotic nature. Some of these strains are only available in their procyclic form which hinders human serum resistance assays and mechanistic studies. Furthermore, the understanding of Tbg2s potential to infect tsetse flies and mammalian hosts is limited. In this study, 165 Glossina palpalis gambiensis flies were experimentally infected with procyclic Tbg2 parasites. 35 days post-infection, 43 flies out of the 80 still alive flies were found Tbg2 PCR-positive in the saliva. These flies were able to infect 3 out of the 4 mice used for blood-feeding. Dissection revealed that only six flies really carried mature infections in their midguts and salivary glands. Importantly, a single fly with a mature infection was sufficient to infect a mammalian host. This Tbg2 transmission success confirms that Tbg2 strains can establish in tsetse flies and infect mammalian hosts. The study describes an effective in vivo protocol for transforming Tbg2 from procyclic to bloodstream form, reproducing the complete Tbg2 cycle from G. p. gambiensis to mice. These findings provide valuable insights into Tbg2s host infectivity, and will facilitate further research on mechanisms of human serum resistance.