Trans-Atlantic Spill Over: Deconstructing the Ecological Adaptation of Leishmania Infantum in the Americas

Abstract

Pathogen fitness landscapes change when transmission cycles establish in non-native environments or spill over into new vectors and hosts. The introduction of Leishmania infantum in the Americas into the Neotropics during European colonization represents a unique case study to investigate mechanisms of ecological adaptation of this important parasite. Defining the evolutionary trajectories that drive L. infantum fitness in this new environment are of great public health importance as they will allow unique insight into pathways of host/pathogen co-evolution and their consequences for region-specific changes in disease manifestation. This review summarizes current knowledge on L. infantum genetic and phenotypic diversity in the Americas and its possible role in the unique epidemiology of VL in the New World. We highlight the importance of appreciating adaptive molecular mechanisms in L. infantum to understand the parasites' successful establishment on the continent.

Revisiting the heterogeneous global genomic population structure of Leishmania infantum

“…4c), and the population structure obtained (POP1) (Fig. 5) support the hypothesis that L. infantum was introduced several times and at several points along the American continent from Europe, possibly during Spanish and Portuguese colonizations [53][54][55][56]. From the evidence, we propose that North African strains were introduced into Colombia possibly during the arrival of African immigrants/slaves [57], as occurred with Plasmodium falciparum, which came to the Americas via the trans-Atlantic slave trade [58].…”

“…Overall, however, L. infantum demonstrated low genetic variability (Fig. 4a), the results obtained in this study suggest there is genetic diversification at a global level in this species, diversification that could be generated by the immense human migrations between countries and/or by the adaptation of the parasite to the distinct genetic structures of the sandfly vector/reservoirs, which have been demonstrated to play an important role in the genetic structure of L. infantum [52,53]. Additionally, we found evidence of the close phylogenomic relationships between genomes from different geographical regions (e.g.…”

“…S4), a property previously ascribed to Brazilian genomes [9,10,14,74]. We consider that this low diversity could be associated with (i) the relatively recent arrival of L. infantum to the Americas [53,55]; (ii) the number of vectors and/or animal reservoirs involved in the transmission cycle [75,76] where L. infantum could have easily adapted, thus favouring certain genotypes and promoting the stochastic loss of others (as has been described in Trypanosoma brucei [77] and suggested for other Leishmania species, such as L. panamensis [72]); or (iii) the low number of samples included in the study (Colombia N=4), which could influence the accuracy of the results. Therefore, additional studies involving representative sampling from Colombia are necessary to confirm these findings.…”

Candidates for Balancing Selection inLeishmania donovaniComplex Parasites

“…4 , Supplementary Material online ). It is possible that this is due to the accumulation of weakly deleterious indel alleles when the Brazilian population was established from European L. infantum populations ( Boité et al 2019 ).…”