• Brucellosis is caused by Brucella canis, which is a gram negative coccobacillus.
  

Clinical signs

• Clinical signs may vary from none to mild. 

• Fever is uncommon because there is no endotoxin to induce a fever.  

• The CBC is usually normal, but there is a general lymphadenopathy because of the reticuloendothelial cell stimulation. This may result in some spleen and liver enlargement.  

• Other signs may include weight loss, poor hair, listless attitude. Some classic signs include thoracic or lumbar diskospondylitis, and endopthalmitis and uveitis caused by immune complex deposits in the eye.  

• In the female ABORTION at 30-50 days of normal-partly autolyzed pups, or live and stillborn pups. The bitch is bacteremic 2-3 months, but otherwise healthy, even though a vaginal discharge may be present. 

• A bitch may lose 2-3 litters in succession. It may appear that INFERTILITY is a problem as early embryonic death may occurr at 20 days, or fetal resorption produces focal necrosis of chorionic villi and bacteria in trophoblastic epithelial cells.  

• Signs in the male may also include infertility as well as epididymitis, orchitis, and scrotal dermatitis that results from scrotal licking due to orchitis. 

  • Testicular atrophy and azoospermia may be seen.

  • Up to 90% sperm abnormalities, head to head sperm agglutination, sperm phagocytosis, and PMN's and monocytes in the semen.
    

Transmission 

• Transmission is primarily venereal and oral (i.e through the mucous membrane)

• There are 2 X 10⁶ colony forming units in an infective dose and 10¹⁰ organisms /ml in the discharge, which means there are 500 infectious doses/ml. 

• The discharge may continue for 4-6 weeks post abortion.  

• The semen only has high numbers of bacteria for 1-2 months, but the disease spreads via the semen anyway.  

• Kennelmate to kennelmate transmission was not seen experimentally when dogs of the same sex were housed next to each other for 10 months. Therefore urine and indirect mucous membranes contact are not important routes of transmission. 

• The aerosol route is only important if conditions are crowded. The milk may contain the organisms.
  

Pathophysiology  

• The bacteria attaches to the mucous membrane and penetrates, with more attachments increasing the virulence. 

• There is a bacteremia that starts 20 days post exposure and the bug spreads to the lymph nodes and is transported to reticuloendothelial cells, prostate, uterus, and placenta. 

• It grows intracellularly in steroid sensitive tissue mostly. 

• The animal then become a source of bacteremia with episodes that last for years.  

• In males there is epididymitis, and sperm leakage that causes antisperm antibodies to develop.  

• In the bitch there is a placentitis, whose exact mechanism is unknown.
  

Recovery  

• Spontaneous recovery can occur 1-3 years post infection, followed by a decrease in the titer. 

• The titer does not rise again if the animal is challenged and re-infection does not occur because cellular immunity is most important.
  
  

Diagnosis

• Culture

• Culture from the blood, lymph nodes, marrow, urine, milk, vaginal discharges or semen is the only definitive diagnosis. 

• Experimentally the organism was seen in 100 % of the dogs at 2 months post infection and the bacteremia lasted 6- 12 months. 

• The organism was recovered in 100% of the males, and 30% of the females in tissues (lymph node, spleen) when they were abacteremic.
  
  

Rapid Slide Agglutination Test (RSAT, 'Card Test')

• The RSAT uses B. ovis bengal stained antigen because it just works better than B. canis antigen.
• The test is performed by mixing the antigen with the patients serum. A precipitate means the test is positive.
• There can be as high as a 60% false positives because of Bordatella, Pseudomonas, Moraxella, B. ovis titers.
• The test becomes positive 2 to 8 weeks post infection and remains positive 40 to 60 months post infection.
• False negatives are very rare. One scenario you may see is a 'false negative'  when the recently infected bitch is less than 8 weeks into the disease and the titer has actually not yet become positive.
• Otherwise, a negative test is usually indicative of a negative dog.
• If the test is positive, further testing is needed because of the high incidence of false positive tests.
  
  

2ME-RSAT

• This test is the same as the RSAT except mercaptoethanol is added to eliminate nonspecific binding of 19S agglutinins, although it too may not be accurate.
  
  

Tube Agglutination Titer (TAT)

• In this test B. canis antigen is diluted and sera is added to determine the titer.
• If the titer is greater than 1:200, it is positive and 1:50 to 1:200 is suspicious.
• This becomes positive 4-8 weeks post infection and then becomes negative 40-60 months post infection.

2ME-TAT

• Same as TAT except 2ME added and there is practically no difference in sensitivity
  
  

Agar Gel Immuno Diffusion (AGID) using the cell wall antigen

• This test becomes positive 8-12 weeks post infection and becomes negative 40-50 months post infection. When the bacteremia stops, the titer declines.

AGID using the cytoplasmic antigen

• This test becomes positive 8-12 weeks post infection and did not become negative for 64 months (lifelong) post infection experimentally.

• This test is very specific for Brucella sp., and a positive test is used diagnostically to confirm RSAT positive tests.
  

Summary of diagnosis

• Use the RSAT, 2ME-RSAT to screen and identify all negative animals.

• Use the AGID cell wall antigen test to confirm the disease.

• Culture is the only definitive diagnosis and is the best diagnostic test in the first 2 months of the disease, however dogs become abacteremic after 27-64 months.
  

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Click to hear an explanation of the graph

Treatment

• Consider that there is no treatment because the cells are harbored intracellularly and the titers decrease with time.
• Ovariohsyterectomy or castration are the best control methods as they remove the steroids that enhance organism life.
  

Drugs

• Ampicillin (10 mg/kg TID 3 weeks) or LA 200 (20 mg/kg weekly 4 weeks) or Tetracycline (20 mg/kg TID 3 weeks) followed by Strep. (20 mg/kg TID 3 weeks)
• Minocycline (25 mg/kg BID 2 weeks and Strep. (20 mg/kg BID 2 weeks), but this is very expensive !!!
• Nicoletti recommends tetracycline (20 mg/kg, q 8 hr, PO, 4 wks), gentamicin (1.5 mg/kg, q 8 hr, SC, 1 wk; or 2.5-3.0 mg/kg, BID). Dogs have successfully reproduced after this treatment.
• Treatment during pregnancy decreases chance of abortion.
• 'Cures' should be suspect as the bug is intracellular and titers decrease with time. The drugs may lead to a transient abacteremia and fall in titer which is interpreted as a 'cure'.
• The flourinated quinilones offer hope for a treatment.
• I would never treat a male because there is too much chance that he could still spread the disease to a bitch.
  
  

Prevention

• B. canis testing every 6 months and before each breeding. Have two negative tests 1 month apart prior to introduction of a new dog.
• Have proper kennel hygiene. Use quaternary ammonium and iodophor disinfectants. The organism is more hardy than some Brucella.
• Eliminate all infected dogs. Keeping positive dogs in a kennel because they are needed to produce puppies only decreases the net number of puppies compared to if they were eliminated.
• Kennels may be safe after 3 negative tests of all dogs.
  
  

Public health

• The zoonotic potential is a concern, but not an alarm. There have been 30 cases reported, and mostly in kennel people with very few in pet owners.