Epidemiological implications of parasite distributions
T. cruzi presents great genetic diversity and is classified by consensus into six DTUs named TcI to TcVI.32 The relevance of T. cruzi genetic diversity in Chagas disease should be examined further but existing evidence supports the importance of this diversity in terms of epidemiology and its association with clinical presentation and outcomes.
Different DTUs are associated with different biological cycles of transmission and seem to have varying geographical distributions.41 TcI, the most frequent and widely distributed DTU, has been found from the South of the United States to the North of Chile and Argentina, and can be transmitted both in sylvatic and domestic cycles. TcIII and TcIV have been more frequently associated with sylvatic cycles, and have been implicated as a cause of acute outbreaks in the Amazon basin.42,43 TcIII has also been found in armadillos,44 although it has been identified from domestic dogs as well,45 and associated to the terrestrial niche even in the Chaco region.46,47 While TcIV seemed to have an arboreal ecotope45 and is the second most frequent DTU detected in Venezuela.48 TcII, TcV, and TcVI have been more often associated with domestic cycles in the Southern Cone countries. Some authors have identified a differential tissue tropism among these DTUs and linked some of them to specific clinical presentations. For instance, TcI has been associated with cardiac disease in Colombia, Argentina, Venezuela, and Brazil49,50; TcII, TcV, and TcVI can cause both cardiac and digestive disease, even causing megasyndromes. In addition, T. cruzi’s genetic diversity seems to confer different drug susceptibility both in vitro,51,52 although this does not seem to influence the clinical outcome,53 and in vivo54 (Fig. 5.2).
Figure 5.2 Geographical distributions of Trypanosoma cruzi discrete typing units (DTUs) and its association with the domestic and silvatic cycles and human pathogenesis.