| Brucella abortus is a bacterial pathogen that infects cattle, other livestock, and wildlife worldwide. Due to the domestication of cattle and its high degree of infectivity, B. abortus is easily transferred among beef and dairy populations through the livestock trade. Understanding how this pathogen has spread globally has been challenging due to a lack of genetic resolution with available methods. Whole genome sequencing allows for a deeper understanding of phylogenetic relationships among bacterial strains. We utilized single nucleotide polymorphisms (SNPs) from 435 B. abortus whole genome sequences to construct a global phylogeny. Resulting analyses suggest Africa as the likely source of B. abortus because this continent contains the most basal lineages as well as the lineages with the highest genetic diversity. Within the hundreds of well-known and common strains from biovars 1 2, and 4 there were extremely low levels of genetic diversity, consistent with findings from other genetic analyses. These three biovars appear to have recently emerged and spread rapidly across the globe. Our collection of isolates is fairly biased, with most samples from North America and Europe. Portions of the world, such as much of Africa, India, and Brazil, are poorly sampled but likely contain important sources of genetic diversity within B. abortus. Whole genome sequencing allows for an unprecedented understanding of B. abortus evolution and should continue to provide insights into novel lineages as more isolates are discovered and sequenced. |
