title: Dispersal of Mycobacterium tuberculosis via the Canadian fur trade.
abstract: Patterns of gene flow can have marked effects on the evolution of populations. To better understand the migration dynamics of Mycobacterium tuberculosis, we studied genetic data from European M. tuberculosis lineages currently circulating in Aboriginal and French Canadian communities. A single M. tuberculosis lineage, characterized by the DS6(Quebec) genomic deletion, is at highest frequency among Aboriginal populations in Ontario, Saskatchewan, and Alberta; this bacterial lineage is also dominant among tuberculosis (TB) cases in French Canadians resident in Quebec. Substantial contact between these human populations is limited to a specific historical era (1710-1870), during which individuals from these populations met to barter furs. Statistical analyses of extant M. tuberculosis minisatellite data are consistent with Quebec as a source population for M. tuberculosis gene flow into Aboriginal populations during the fur trade era. Historical and genetic analyses suggest that tiny M. tuberculosis populations persisted for ∼100 y among indigenous populations and subsequently expanded in the late 19th century after environmental changes favoring the pathogen. Our study suggests that spread of TB can occur by two asynchronous processes: (i) dispersal of M. tuberculosis by minimal numbers of human migrants, during which small pathogen populations are sustained by ongoing migration and slow disease dynamics, and (ii) expansion of the M. tuberculosis population facilitated by shifts in host ecology. If generalizable, these migration dynamics can help explain the low DNA sequence diversity observed among isolates of M. tuberculosis and the difficulties in global elimination of tuberculosis, as small, widely dispersed pathogen populations are difficult both to detect and to eradicate.
authors.affiliation: Division of Infectious Diseases, Stanford University, Stanford, CA 94305, USA. pepperc@stanford.edu
authors.forename: Caitlin S
authors.initials: CS
authors.lastname: Pepperell
authors.forename: Julie M
authors.initials: JM
authors.lastname: Granka
authors.forename: David C
authors.initials: DC
authors.lastname: Alexander
authors.forename: Marcel A
authors.initials: MA
authors.lastname: Behr
authors.forename: Linda
authors.initials: L
authors.lastname: Chui
authors.forename: Janet
authors.initials: J
authors.lastname: Gordon
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Guthrie
authors.forename: Frances B
authors.initials: FB
authors.lastname: Jamieson
authors.forename: Deanne
authors.initials: D
authors.lastname: Langlois-Klassen
authors.forename: Richard
authors.initials: R
authors.lastname: Long
authors.forename: Dao
authors.initials: D
authors.lastname: Nguyen
authors.forename: Wendy
authors.initials: W
authors.lastname: Wobeser
authors.forename: Marcus W
authors.initials: MW
authors.lastname: Feldman
mesh_terms: D002170:Canada; D004269:DNA, Bacterial / Q000235:genetics*; D004641:Emigration and Immigration / Q000266:history*; D051456:Gene Flow; D049670:History, 17th Century; D049671:History, 18th Century; D049672:History, 19th Century; D006801:Humans; D007198:Indians, North American / Q000266:history*; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D014376:Tuberculosis / Q000453:epidemiology / Q000235:genetics / Q000266:history; D044465:White People / Q000266:history*
chemical_list: D004269:DNA, Bacterial