North American import? Charting the origins of an enigmatic Trypanosoma cruzi domestic genotype.
BACKGROUND
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 - TcI(DOM). TcI(DOM). 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 TcI(DOM) genotype. We propose two possible scenarios: an emergence of TcI(DOM) 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.


RESULTS
Mitochondrial sequence and nuclear microsatellite data revealed a cline in genetic diversity across isolates grouped into three populations: South America, North/Central America and TcI(DOM). As such, greatest diversity was observed in South America (A(r) = 4.851, π = 0.00712) and lowest in TcI(DOM) (Ar = 1.813, π = 0.00071). Nuclear genetic clustering (genetic distance based) analyses suggest that TcI(DOM) is nested within the North/Central American clade.


CONCLUSIONS
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.
Centro Regional de Investigación en Salud Pública, Instituto Nacional de Salud Pública, Tapachula, Chiapas, México.
Federico A
FA
Zumaya-Estrada
Louisa A
LA
Messenger
Teresa
T
Lopez-Ordonez
Michael D
MD
Lewis
Carlos A
CA
Flores-Lopez
Alejandro J
AJ
Martínez-Ibarra
Pamela M
PM
Pennington
Celia
C
Cordon-Rosales
Hernan V
HV
Carrasco
Maikel
M
Segovia
Michael A
MA
Miles
Martin S
MS
Llewellyn
D000818:Animals; D002489:Central America; D016000:Cluster Analysis; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D008969:Molecular Sequence Data; D009656:North America; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013020:South America; D014349:Trypanosoma cruzi / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification
D016054:DNA, Protozoan