Remarkable genetic diversity of Trypanosoma cruzi and Trypanosoma rangeli in two localities of southern Ecuador identified via deep sequencing of mini-exon gene amplicons

Abstract

Trypanosoma cruzi, causative agent of Chagas disease, and T. rangeli are kinetoplastid parasites endemic to Latin America. Although closely-related to T. cruzi and capable of infecting humans, T. rangeli is non-pathogenic. Both parasite species are transmitted by triatomine bugs, and the presence of T. rangeli constitutes a confounding factor in the study of Chagas prevalence and transmission dynamics. T. cruzi possesses high molecular heterogeneity: six discrete typing units (DTUs) are currently recognized. In Ecuador, TcI predominates while other DTUs are seldom reported. Here, infection by T. cruzi and/or T. rangeli in triatomine bugs from two communities of southern Ecuador was evaluated via PCR product size polymorphism of kinetoplast-minicircle sequences and the non-transcribed spacer region of the mini-exon gene. Additionally, mini-exon amplicons were deep-sequenced to analyze single nucleotide polymorphisms and mixed infections. As a control, mini-exon products from several monoclonal reference strains were included. T. cruzi genetic diversity was significantly greater in adult vectors than in nymphal stage V vectors. Among infected triatomines, deep sequencing revealed one T. rangeli infection (3%), 9 T. cruzi infections (27.3%) and 23 T. cruzi / T. rangeli mixed infections (69.7%), suggesting that T. rangeli prevalence has been largely underestimated in the region. Furthermore, deep-sequencing detected TcIV sequences in six samples (first TcIV record in southern Ecuador). Our data indicate that amplicon size analysis alone is not reliable for parasite identification/typing in mixed infections containing both T. cruzi and T. rangeli, or when multiple T. cruzi DTUs are present. Additionally, our analysis showed extensive overlap among the parasite populations present in the two studied localities (ca. 28 km apart); suggesting active parasite dispersal over the study area. Our results highlight the value of amplicon sequencing methodologies to clarify the population dynamics of kinetoplastid parasites in endemic regions and inform control campaigns in southern Ecuador.