O2-5 Whole genome based tools in epidemiological surveillance of Brucella abortus, Brucella melitensis and Brucella suis bv2 in Italy in the last decade.

Abstract

Brucellosis is one of the most important zoonotic diseases in the Mediterranean basin. In Italy, Brucella abortus and B. melitensis, prevalent in the southern regions despite the ongoing eradication campaign, continue to pose public health risk and cause significant economic losses. In this work we use genomic tools to study the epidemiology of B. abortus, B. melitensis and B. suis bv2 in Italy over the last decade. We sequenced over 1,300 Brucella strains collected between 2011 and 2021. The sequences were typed using whole genome sequencing (WGS)-based methods, including single nucleotide polymorphism (SNP) and core genome multilocus sequence typing (cgMLST) and clusters of genetically related strains were identified. WGS typing results demonstrated the presence of three large clusters of B. abortus,  corresponding to diverse sequence types. ST-30 was dominant in Sicily, while ST-1 and ST-2 were found mostly in mainland Italy. ST-1 strains, all assigned to biovar 1 were collected primarily from buffalo and largely restricted to Campania region. These strains formed a tight genomic cluster that has persisted in the region for the entire decade. B. melitensis was predominantly found in the south, with the highest prevalence in Sicily and Calabria. While in these regions we observed weak geographical segregation of the genotypes, the incursions of B. melitensis in the northern regions were generally caused by single clone introductions. Half of the cases of human brucellosis could be attributed to the locally circulating B. melitensis strains, while the others were mainly imported from North Africa. The population of B. suis bv2 from the wild boars and pigs in Italy was grouped in several lineages. Central European lineage, confined to the northwestern regions, and Eastern European lineage, found along the Apennine mountain ridge, both contained highly clonal strains suggesting that they arose from single introduction events, likely linked to the wild boar repopulation campaigns. Our study demonstrates that a large number of Brucella clones persisted over many years in Italy, escaping the control measures imposed in the eradication programmes. Integrating WGS analysis of Brucella strains with the current control strategies would be vital for more effective eradication campaign in Italy.