North American import? Charting the origins of an enigmatic Trypanosoma cruzi domestic genotype
1 Centro Regional de Investigación en Salud Pública, Instituto Nacional de Salud Pública, Tapachula, Chiapas, México
2 London School of Hygiene and Tropical Medicine, London, UK
3 Department of Biology, University of Maryland, College Park, MD, USA
4 Área de Entomología Médica, Centro Universitario del Sur, Universidad de Guadalajara, Ciudad Guzmán, Jalisco, México
5 Center for Health Studies, Research Institute, Universidad del Valle de Guatemala, Guatemala City, Guatemala
6 Instituto de Medicina Tropical, Universidad Central de Venezuela, Caracas, Venezuela
Parasites & Vectors 2012, 5:226 doi:10.1186/1756-3305-5-226Published: 10 October 2012
Trypanosoma cruzi, the agent of Chagas disease, is currently recognized as a complex of six lineages or Discrete Typing Units (DTU): TcI-TcVI. Recent studies have identified a divergent group within TcI - TcIDOM. TcIDOM. is associated with a significant proportion of human TcI infections in South America, largely absent from local wild mammals and vectors, yet closely related to sylvatic strains in North/Central America. Our aim was to examine hypotheses describing the origin of the TcIDOM genotype. We propose two possible scenarios: an emergence of TcIDOM in northern South America as a sister group of North American strain progenitors and dispersal among domestic transmission cycles, or an origin in North America, prior to dispersal back into South American domestic cycles. To provide further insight we undertook high resolution nuclear and mitochondrial genotyping of multiple Central American strains (from areas of México and Guatemala) and included them in an analysis with other published data.
Mitochondrial sequence and nuclear microsatellite data revealed a cline in genetic diversity across isolates grouped into three populations: South America, North/Central America and TcIDOM. As such, greatest diversity was observed in South America (Ar = 4.851, π = 0.00712) and lowest in TcIDOM (Ar = 1.813, π = 0.00071). Nuclear genetic clustering (genetic distance based) analyses suggest that TcIDOM is nested within the North/Central American clade.
Declining genetic diversity across the populations, and corresponding hierarchical clustering suggest that emergence of this important human genotype most likely occurred in North/Central America before moving southwards. These data are consistent with early patterns of human dispersal into South America.