Brucellosis

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Interstitial lymphoplasmacytic and histiocytic infiltration of the prostate gland with fibrosis and occasional disruption of glandular profiles
Brucella infection in the reproductive tract of dogs: a) Lymphohistiocytic proliferation of splenic white pulp - a consistent lesion in females. b) In male dogs, the splenic white pulp is unremarkable
Brucellosis in dogs: a) Chorioallantoic membrane lined by distended, bacteria-laden trophoblasts. Hematoxylin and eosin. Bar = 50 μm. b) Higher magnification of trophoblasts c) Gram-negative bacteria within trophoblasts d) Avidin-biotin complex immunoenzyme staining of trophoblasts, using pooled canine sera from infected dogs diluted in PBS/1% ovalbumin to a concentration of 1:200 as primary antibody

Although dogs occasionally become infected with Brucella abortus , B suis , or B melitensis, these sporadic occurrences are usually closely associated with infected domestic livestock. Brucella canis is a potential zoonotic agent that infects dogs and wild canidae almost exclusively. Infection by B. canis is suspected in male dogs that have epididymitis or are infertile, and in female dogs that abort in late gestation or fail to conceive. Occasionally, infection may manifest as systemic disease in various organs, including bone, eyes, and, rarely, brain. Brucella canis is spread via contact with the genitourinary secretions from infected dogs, including aborted placental and fetal material, vaginal secretions from infected females that are in heat, prostatic and seminal fluid, and urine. Following abortion, females may continue to shed bacteria intermittently for weeks or months[1].

Cause

B canis is a cause of abortion in kenneled dogs. Dogs are the definitive host of this organism, and natural infections in other animals are rare. Infection has caused a reduction of 75% in the number of pups weaned in some breeding kennels. The disease disseminates rapidly among closely confined dogs, especially at time of breeding or when abortions occur. Transmission occurs via ingestion of contaminated materials or venereal routes. Both sexes appear to be equally susceptible. Transmission of brucellosis from dogs to humans occurs but appears to be very rare[2].

Clinical signs

Primary signs are abortion during the last trimester of pregnancy without premonitory signs, stillbirths, and conception failures. Prolonged vaginal discharge usually follows abortion. Abortions may occur during subsequent pregnancies. Infected dogs may develop generalized lymphadenitis and frequently epididymitis, periorchitis, and prostatitis. Spondylitis and uveitis are occasional complications. Bacteremia is frequent and persists for ~18 mo after exposure. Fever is not characteristic[3].

Diagnosis

Antemortem diagnosis of B. canis infection in dogs typically relies on serological testing, supported by confirmatory blood culture. Diagnosis can be challenging, with serological false-positives ranging between less than 10% and 75%, depending on the method used[4].

The organisms can usually be readily isolated from vaginal exudate, aborted pups, blood, milk, or semen of infected dogs. The most widely used serologic test is an agglutination test by a tube or slide method. Nonspecific agglutination reactions occur in some dogs from which Brucella has not been isolated. To eliminate nonspecific antibodies, the serum is treated with 2-mercaptoethanol and retested. An agar gel immunodiffusion test performed in some laboratories is quite specific.

Treatment

Attempts at immunization have not been successful. Control is based on elimination or isolation of infected dogs identified by positive cultural or serologic tests. Incidence of infection is much lower in kennels where dogs are caged individually. Brucellosis is very difficult to treat successfully. A combination of minocycline and streptomycin is thought to be most effective but is expensive. Tetracycline can be substituted for the minocylcine to reduce costs but also lowers the effectiveness of treatment. All infected animals should be neutered or spayed to prevent sexually related transmission. All infected animals should be considered to be lifelong carriers of the disease, even if treated.

It would probably be best not to breed dogs without testing both the male and female for this disease. Breeding should be a deliberate choice -- not a random event! For breeding kennels, routine isolation of new dogs would be a very good idea. After isolation and negative tests at entry into the kennel and one month later, it should be safe to let the new dog mix with the others in the kennel. If infection is suspected at any time, quaternary ammomium (like Roccal Rx) and iodophor (Betadine Rx) disinfectants can kill Brucella organisms in the kennel to limit spread of the disease.

References

  1. Carmichael LE, Greene CE (2006) Canine brucellosis. In: Greene CE, editor. Infectious Diseases of the Dog and Cat. 3. Philadelphia: Elsevier Saunders; pp:369–381
  2. Merck Veterinary Manual
  3. Bosu WTK, Prescott JF (1980) A serological survey of dogs for Brucella canis in southwestern Ontario. Can Vet J 21:198–200
  4. Carmichael LE, Shin SJ (1996) Canine brucellosis: A diagnostician’s dilemma. Semin Vet Med Surg (Small Anim) 11:161–165