title: Clonal origin of emerging populations of Ehrlichia ruminantium in Burkina Faso.
abstract: Cowdriosis or heartwater is a major tick-borne disease on ruminants in Africa and the Caribbean. The causative agent is Ehrlichia ruminantium, an intracellular bacterium. Development of vaccines against heartwater has been hampered the limited efficiency of vaccine in the field, thought to be a consequence of the high genetic diversity of strains circulating in a same area. A sampling scheme was set to collect ticks over 2 years in a delimited area and well identified flock. Prevalence was low at about 3%. A set of 37 strains was considered for MLST analysis along with two reference strains, i.e. ERGA and ERWO, for which full-length genome was available, using a previously described scheme based on the genes gltA, groEL, lepA, lipA, lipB, secY, sodB and sucA. Two populations were identified both with limited genetic variability but with differing evolutionary patterns. Population 1 is in genomic stasis, in agreement with the paradigm for intracellular bacteria. The two reference strains, one from the Caribbean separated from West African strains three centuries ago and another one isolated in South Africa, belong to Population 1. Population 2 is on expansion following a recent clonal emergence from Population 1. The founder strain was identified as strain 395. Strain 623 displays a particularly high rate of mutations in groEL. Owing to the chaperone function of GroEL, this might indicate another clonal emergence under way. This work brings further insight in the genomic plasticity of E. ruminantium and its impact on vaccine strategy.
authors.affiliation: CIRDES Laboratoire de Biotechnologie (URBIO), 559, 3-51 Avenue du Gouverneur Louveau, B.P. 454, Bobo-Dioulasso, Burkina Faso, France. hassaneadakal@yahoo.fr
authors.forename: Hassane
authors.initials: H
authors.lastname: Adakal
authors.forename: Laurent
authors.initials: L
authors.lastname: Gavotte
authors.forename: Frédéric
authors.initials: F
authors.lastname: Stachurski
authors.forename: Maurice
authors.initials: M
authors.lastname: Konkobo
authors.forename: Hélène
authors.initials: H
authors.lastname: Henri
authors.forename: Sébastien
authors.initials: S
authors.lastname: Zoungrana
authors.forename: Karine
authors.initials: K
authors.lastname: Huber
authors.forename: Nathalie
authors.initials: N
authors.lastname: Vachiery
authors.forename: Dominique
authors.initials: D
authors.lastname: Martinez
authors.forename: Serge
authors.initials: S
authors.lastname: Morand
authors.forename: Roger
authors.initials: R
authors.lastname: Frutos
mesh_terms: D000818:Animals; D002050:Burkina Faso / Q000453:epidemiology; D016995:Ehrlichia ruminantium / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D006239:Haplotypes; D026863:Ixodidae / Q000382:microbiology; D015810:Linkage Disequilibrium; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic