Experimental and natural recombination in Trypanosoma cruzi

T. cruzi comprises six lineages or DTUs (discrete typing units), designated as TcI to TcVI, with characteristic geographical, ecological, transmission cycle, and disease associations. TcII, TcV, and TcVI are the main causes of Chagas disease in the Southern Cone countries of South America, whereas TcI is the principal agent of Chagas disease in Latin America north of the Amazon basin. The reproductive mode of T. cruzi has been considered to be predominantly clonal. However, an experimental cross between TcI clones demonstrated that T. cruzi has an extant capacity for genetic exchange, with an unusual mechanism of fusion of diploids followed by genome erosion, producing aneuploid hybrids. Furthermore, TcV and TcVI are naturally occurring interlineage hybrids of TcII and TcIII, which have a recent origin and probably spread in association with the domestic vector Triatoma infestans. Recent evidence of mitochondrial introgression at both the inter- and intralineage level and panmixia in restricted populations suggests that genetic exchange may be more pervasive than previously thought. Recombination in T. cruzi clearly has profound evolutionary and epidemiological significance, although the frequency and mechanisms operating in natural populations remain incompletely understood