First isolation and identification of Brucella microti in sheep and goats: New insights and implications for veterinary medicine

Luca Freddi^1*Vitomir DJOKIC¹Alexandre Dremeau¹Maëline Ribeiro¹Maxime Berthaud²Florence Bennasar³Cyril Pailhous⁴Adeline Lanterne⁵Acacia Ferreira Vicente¹Claire PONSART¹

• ¹Agence Nationale de Sécurité Sanitaire de l’Alimentation, de l’Environnement et du Travail (ANSES), Maisons-Alfort, France
• ²Anses Laboratoire de Ploufragan-Plouzane, Ploufragan, France
• ³Departmental laboratory of Haute-Garonne (LD31 EVA), 31140 Launaguet, France
• ⁴DDETSPP de l’Aveyron, Bouran, France
• ⁵Departement des Pyrenees-Atlantiques, Pau, France

Many species from the genus Brucella are causative agents of the bacterial zoonosis brucellosis. Until recently it was generally believed that these bacteria exhibit strict host specificity, however, recent findings suggest otherwise. Brucella microti is an atypical Brucella species, no threat to humans, with a broad host spectrum, primarily found in wildlife, rodents, and the only Brucella species isolated from soil, aquatic environments and frogs suggesting its environmental persistence, and adaptability to diverse ecological niches. Despite its environmental resilience and wide host range, B. microti has not been identified detected in domestic animals. This study, for the first time, shows the ability of B. microti to infect domestic small ruminants. During the 2024 prophylaxis campaigns across three farms in two French departments, two sheep and one goat tested positive on classical serological tests for brucellosis.Following bacteriological isolation, HRM-PCR and classical biotyping methods classified the strains as B. microti, rather than the expected zoonotic Brucella spp. (B. abortus, B. suis, and B. melitensis). Using hHybrid whole-genome sequencing, wgSNP and MLVA analyses revealed that the three isolates were genetically closer to the referent B. microti CCM4915 strains, isolated in Central Europe, than previously detected French strains from farmed frogs. The B. microti infection of small ruminants by B.microti is even more unusual, because as no strain-specific antimicrobial resistance nor virulence genes were identified found. These findings underscore the need for new diagnostic tools that can identify Brucellae on species level for proper management and monitoring, particularly in regions with epizootic risks. Further research is essential to clarify B. microti's role in animal health and risks for public health.