Brucella canis is an intracellular pathogen that induces a lower proinflammatory response than smooth zoonotic counterparts.

Canine brucellosis caused by Brucella canis is a disease of dogs and a zoonotic risk. B. canis harbors most of the virulence determinants defined for the genus, but its pathogenic strategy remains unclear since it has not been demonstrated that this natural rough bacterium is an intracellular pathogen. Studies of B. canis outbreaks in kennel facilities indicated that infected dogs displaying clinical signs did not present hematological alterations. A virulent B. canis strain isolated from those outbreaks readily replicated in different organs of mice for a protracted period. However, the levels of tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-12 in serum were close to background levels. Furthermore, B. canis induced lower levels of gamma interferon, less inflammation of the spleen, and a reduced number of granulomas in the liver in mice than did B. abortus. When the interaction of B. canis with cells was studied ex vivo, two patterns were observed, a predominant scattered cell-associated pattern of nonviable bacteria and an infrequent intracellular replicative pattern of viable bacteria in a perinuclear location. The second pattern, responsible for the increase in intracellular multiplication, was dependent on the type IV secretion system VirB and was seen only if the inoculum used for cell infections was in early exponential phase. Intracellular replicative B. canis followed an intracellular trafficking route undistinguishable from that of B. abortus. Although B. canis induces a lower proinflammatory response and has a stealthier replication cycle, it still displays the pathogenic properties of the genus and the ability to persist in infected organs based on the ability to multiply intracellularly.

The first detection of Brucella canis in cattle in the Republic of Korea.

Twenty mammary lymph node samples were collected from cattle on a farm in the Republic of Korea. These cattle were serologically negative for Brucella by tube agglutination test (≤ 1:50) and serum agglutination test (≤ 1:50). Out of 20 lymph node samples, two samples were positive for Brucella growth on Brucella agar as well as blood agar. Tests for urease, hydrogen sulphide and reactions against monospecific sera A and M indicated that these two isolates (No. 15 and 16) belong to the genus Brucella. Genus specific, AMOS (abortus, melitensis, ovis, suis) and Bruce-ladder multiplex polymerase chain reaction (PCR) assays confirmed the Brucella isolates as either a B. abortus or a B. canis strain. This is the first report of the occurrence of a B. canis infection in cattle in Korea. More survey data are needed to determine whether B. canis is a significant aetiology in the cases of cattle brucellosis in Korea.

Use of enrofloxacin in the treatment of canine brucellosis in a dog kennel (clinical trial).

To date, no totally effective antibiotic for the eradication of canine brucellosis has been found. The purpose of this study was to evaluate the efficacy of enrofloxacin in a kennel infected with Brucella canis. Twelve dogs, 2 males and 10 females (including 1 in estrus, 3 pregnant, and 6 in anestrus) infected with B. canis were given 5 mg/kg of enrofloxacin orally every 12 h for 30 days. Females received additional courses of enrofloxacin during the estral and luteal phases of the subsequent cycles (0-2 cycles). They were repeatedly mated by infected males. A serological follow-up was carried out for 38 months. The clinical, serological and bacteriological findings were recorded. In a trial carried out 14 months after the beginning of this study, all dogs were negative on the Rapid Slide Agglutination Test (RSAT). No abortions were observed. All mated female dogs conceived and gave birth to healthy puppies. Cultures of postpartum vaginal discharges (lochia) were negative for B. canis. Similar to other treatments, although enrofloxacin was not completely efficacious in treating canine brucellosis, it maintained fertility and avoided the recurrence of abortions, transmission of the disease to the puppies and dissemination of microorganisms during parturition. We inferred that enrofloxacin could be used as an alternative drug for the treatment of canine brucellosis.