Evolutionary ecology of Chagas disease; what do we know and what do we need?

The aetiological agent of Chagas disease, Trypanosoma cruzi, is a key human pathogen afflicting most populations of Latin America. This vectorborne parasite is transmitted by haematophageous triatomines, whose control by large-scale insecticide spraying has been the main strategy to limit the impact of the disease for over 25 years. While those international initiatives have been successful in highly endemic areas, this systematic approach is now challenged by the emergence of insecticide resistance and by its low efficacy in controlling species that are only partially adapted to human habitat. In this contribution, we review evidences that Chagas disease control shall now be entering a second stage that will rely on a better understanding of triatomines adaptive potential, which requires promoting microevolutionary studies and -omic approaches. Concomitantly, we show that our knowledge of the determinants of the evolution of T. cruzi high diversity and low virulence remains too limiting to design evolution-proof strategies, while such attributes may be part of the future of Chagas disease control after the 2020 WHO's target of regional elimination of intradomiciliary transmission has been reached. We should then aim at developing a theory of T. cruzi virulence evolution that we anticipate to provide an interesting enrichment of the general theory according to the specificities of transmission of this very generalist stercorarian trypanosome. We stress that many ecological data required to better understand selective pressures acting on vector and parasite populations are already available as they have been meticulously accumulated in the last century of field research. Although more specific information will surely be needed, an effective research strategy would be to integrate data into the conceptual and theoretical framework of evolutionary ecology and life-history evolution that provide the quantitative backgrounds necessary to understand and possibly anticipate adaptive responses to public health interventions.

Time variability of the north-western Mediterranean Sea pH over 1995-2011.

Factors controlling ocean acidification and its temporal variations were studied over the 1995-2011 period at the Dyfamed site at 10 m depth, in the North Mediterranean Sea. The results indicated a mean annual decrease of 0.003 ± 0.001 pH units on the seawater scale. The seasonal variability was characterized by a pH decrease during springtime and a strong pH increase in late fall. Anthropogenic CO2 (CANT) absorption by the ocean was the key driver of seawater acidification in this region, accounting for about 70% of the observed drop in pH, followed by water temperature (about 30%). The total inorganic carbon (CT) data showed a CT increase of 30.0 ± 1.0 µmol kg(-1) per decade. This decadal increase is mainly due to the CANT penetration (43.2 µmol kg(-1) per decade) in surface waters, which is mitigated for by relatively small opposing changes in CT due to physical and biological processes.