Identification of Source of Brucella Suis Infection in Human By Whole-Genome Sequencing, United States and Tonga

BACKGROUND: Brucella suis infection was diagnosed in a man originally from Tonga, Polynesia, who had butchered swine in Oregon, USA.  Patient history suggested possible exposure to swine from a commercial production operation. Commercial swine in the US.are considered free of B. suis. The disease is endemic in some feral swine populations, but it has not been found in Oregon, and there are no feral swine geographically close to the operation.

METHODS:  We used whole-genome sequencing (WGS) and single-nucleotide polymorphism (SNP) analysis to compare DNA extracts from this patient with known extracts from past swine cases in the US, and extracts from Tongan subjects supplied by the New Zealand Ministry for Primary Industries. These techniques can provide increased resolution to identify the source of infections without more expensive field investigations and testing.

RESULTS:  We determined that the man was infected in Tonga and not by swine in the US. This averted the need for postexposure treatment of other contacts participating in home slaughter or meat preparation.

CONCLUSIONS: Based on these WGS results, it was not necessary for agriculture officials to test domestic swine from the commercial operation, nor was it required to trace movements of animals to other farms which would also need to be tested. This not only saved considerable time and expense, but also allowed agricultural trade to continue without restrictions.

This case demonstrates the value of an international database of validated WGS isolates that can be used by both public-health and animal-health officials in their collaborative epidemiologic investigations. It highlights the benefits of a One-Health approach to both the human health and livestock sectors, including state, federal, and international authorities.