Brucellosis of the common vole (Microtus arvalis)

A systemic disease occurred in a wild population of the common vole Microtus arvalis in South Moravia (Czech Republic) during the years 1999-2003. Acute infections were characterized by edema of extremities, occasionally with colliquating abscesses, arthritis, lymphadenitis, perforations of the skin resulting from colliquated abscesses, orchitis, and peritoneal granulomas. From the clinical samples, small Gram-negative coccobacilli were isolated and identified as Ochrobactrum intermedium by API 20NE and colistin sensitivity profiles. However, subsequent rrs (16S rRNA) and recA (recombinase A) gene sequencing analysis of two isolates (CCM 4915 = CAPM 6434; CCM 4916 = CAPM 6435) identified them as Brucella sp. with sequence identities of 100% to other Brucella spp. Analysis of the omp2a/b genes confirmed the two isolates as Brucella. In AMOS polymerase chain reaction (PCR), a 2000-bp fragment was generated that was not seen in other brucellae. Experimental infection of outbred ICR mice with these isolates resulted in a mortality rate of 50%. Based on the results of the molecular investigations and the mortality observed in experimentally infected mice we conclude that the epizootic was caused by Brucella sp. and not by Ochrobactrum intermedium. The study demonstrates the limitations of commercial biochemical test systems in accurately differentiating among Ochrobactrum and Brucella.