BRUCELLOSIS (CANINE)

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 BRUCELLOSIS (CANINE)

Nature of the disease
Canine brucellosis is a bacterial disease that causes infertility and abortion in dogs caused by an infection by Brucella canis.
Classification
SPC List D disease
Susceptible species
The dog is the only animal species known to be naturally susceptible to the disease, although antibodies have been found in a number of other carnivore species. B. canis is a low-grade human pathogen, with approximately 30 human cases having been reported.
Distribution
Canine brucellosis has been reported in the United States, Mexico, Japan, Germany, the Czech Republic, the Slovak Republic, Brazil and Madagascar. However, it is probably even more widespread.
Clinical signs 
There is no fever associated with the infection, although an intermittent bacteraemia can persist for two years or longer. Infection of non-gravid bitches is seldom detected clinically. There is:
  • Initial swelling of the retropharyngeal lymph nodes after oral infection and the superficial inguinal and external iliac nodes after vaginal infection
  • Bitches may be temporarily or permanently sterile
  • Fatigue
  • Reduced appetite and weight loss
  • Behavioural abnormalities

In pregnant bitches abortion is usually the first clinical manifestation of the disease:

  • Occurs between the seventh and ninth weeks of pregnancy
  • Mucoid, serosanguinous or grey-green vaginal discharge, lasting for up to six weeks.
  • Live pups are often weak and die within a few days

Male dogs may be infertile and may show epididymitis and orchitis, with varying degrees of prostatitis and testicular atrophy. However, many infected males are clinically normal.

Post-mortem findings 
The most consistent lesions are hyperplasia of lymph nodes and splenitis. Bitches frequently have reticular cell nodules in the endometrium. Male dogs may have testicular fibrosis and atrophy.
Occasionally, there may be:
  • Meningitis
  • Focal non-suppurative encephalitis
  • Osteomyelitis
  • Uveitis
  • Pyogranulomatous dermatitis
  • Raining scrotal ulcers
  • Internal abscesses
Differential diagnosis 
Canine brucellosis is an insidious disease. It may be suspected when abortions occur in the last trimester or when epididymitis and testicular atrophy are observed in male dogs. Infection with beta-haemolytic streptococci and Escherichia coli may produce similar signs in bitches.
Specimens required for diagnosis 
Specimens should be collected from aborted foetuses for bacteriological examination and culture. Specimen should be chilled and transported on water ice.

Samples of foetal gastric contents, liver, spleen and foetal membranes should be collected aseptically into sterile containers. Swabs of vaginal discharges and milk samples should also be collected from aborting bitches. Semen samples should be collected from male dogs.

Blood samples, about 10 ml each, should be collected for serum. The blood clots from these samples should be retained and submitted for bacterial culture.

Transmission   
B. canis can penetrate intact mucous membranes, and is most commonly transmitted by contact with the products of abortion or subsequent vaginal discharges. Venereal transmission also occurs when susceptible bitches are mated with infected dogs.

The organism is excreted in the semen for up to 60 weeks. It is also excreted in urine, but the significance of this in the spread of infection is uncertain.

Risk of introduction   
Canine brucellosis is most likely to be introduced through the importation of infected dogs or canine semen.
Control / vaccines  
Antibiotics can be used to treat individual cases. In kennels, the disease should be controlled by hygiene and elimination of infected dogs.

In breeding establishments, repeat testing and removal of sero-positive dogs, together with isolation and testing of imports has been successful in eradicating the disease.

References
  • Brucellosis in Dogs, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 1043
  • GEERING WA, FORMAN AJ, NUNN MJ, Exotic Diseases of Animals, Aust Gov Publishing Service, Canberra, 1995, 440p