First Isolation of Brucella canis from a breeding kennel in Italy.

Abstract

Brucella canis has been isolated for the first time in Italy in a commercial breeding kennel. It was diagnosed after a deep investigation related to the onset of reproductive disorders. Animals were tested with direct and indirect techniques. The agent was first detected in two Chihuahua aborted foetuses by direct culture. Further, it was also isolated from blood samples of dogs hosted in the kennel, which also showed reaction to conventional serological tests (microplate serum agglutination test). The isolates were identified as B. canis by standard microbiological methods and a Bruce‑ladder multiplex PCR. To investigate the genomic diversity, whole genome sequencing was used, applying the core genome Multilocus Sequence Typing (cgMLST ). In a first round of serological testing performed on 598 animals, 269 (46.1%) tested positive. In the second round of laboratory testing carried out 4‑5 weeks apart, the number of serologically positive dogs was 241 out of 683 tested (35.3%), while the number of dogs positive to isolation was 68 out of 683 tested (10.0%). The PCR showed a lack of sensitivity when compared to direct isolation. The epidemiological investigation did not identify the source of the infection, given the time elapsed from the onset of abortions to the definitive diagnosis of B. canis infection in the kennel. The genomic analyses featured the strains as ST21 and, according to the cgMLST, revealed the presence of a tight cluster with a maximum diversity of four allelic differences. The observed limited genomic variation, largely within the known outbreak cut‑offs, suggests that the outbreak herein described was likely caused by a single introduction. Moreover, in a broader scale comparison using the public available genomes, we found that the closest genome, isolated in China, differed by more than 50 alleles making not possible to find out the likely origin of the outbreak. The lack of updated data on B. canis genome sequences in the public databases, together with the limited information retrieved from the epidemiological investigations on the outbreak, hampered identification of the source of B. canis infection.