Brucellosis may be passed to humans


If you have a female dog and want to find a male to breed with, you may very well be asked to prove that your female dog is Brucellosis negative first. The owner of the male dog wants to make sure his prized dog doesn’t contact this terrible disease while mating. Testing is standard procedure to professional breeders and serious kennels, but the typical pet owner and amateur breeder may not be familiar with the disease.

Like many other diseases, brucellosis used to be a common in our farm animals, greatly reducing production, wreaking financial ruin on families dependent on their farms, causing abortions of calves and piglets, and killing animals and people alike. 

With the advent of modern science and with great expense and effort, veterinarians, government scientists, and farmers worked together in the developing countries to test every cow and hog prior to slaughter or crossing a State line. If an animal turned up positive, the farm was quarantined, and all affected animals were destroyed. The farm wasn’t released from quarantine until multiple follow up tests proved negative. It was a big, big deal, but it proved effective; we vets rarely see a brucellosis case anymore. I haven’t worked in herd health in long time, but I’m pretty sure testing is still routine, especially for animals crossing borders, less this disease find it’s way back into our food animals.

While the disease may be practically eradicated in our livestock, the disease is still present as a strain known as Brucella canis in our canine population. Usually dogs carrying the brucella organism have no outward signs of sickness ... But; the organism loves fetal tissue and causes abortions. Humans coming in contact with the aborted tissue, semen, vaginal discharges, or urine of an affected dog might also harbor the organism with ill effects...especially if pregnant.

The disease is transmitted from one dog to another mostly through sex, but also from contact with vaginal discharges, urine, and aborted placentas and fetuses. One positive dog in a kennel situation could spread the problem to all the other dogs and there might not be any obvious sign that it happened.

But positive females either don’t conceive or have abortions. Males become sterile and may have swollen testicles. Most seem healthy but are capable of spreading the disease to others.

Because of all this, it’s wise for breeders to test both the male and female before breeding. This is something your vet must do for you, but if you plan ahead, he or she can mail your dog’s blood sample for you to your State lab, which usually will do the test quite cheaply, but results make take too long to get back if you’ve waited until your dog is in heat to do the test. The alternative is a more expensive screening test kit that your vet is likely to have with the advantage of results in about 20 minutes. In the rare event that your dog turns up positive, you may be forced to destroy the dog for public health reasons. This won’t be done, however, until the dog is retested with by the official State Veterinarian to ensure that the dog is positive. This too, is a big deal. The State Vet will very likely require any of your other pets, neighbors pets, etc to be tested in an attempt to eradicate the potential threat. Luckily this is a rare event.

There is no treatment or vaccine for this terrible disease.

There is only the legal requirement and hope that animal owners will cooperate if needed and that breeders will test prior to breeding.

By Roger Ross, DVM


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 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.


  • 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.


  • 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 reinfection does not occur because cellular immunity is most important.



  • 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' is 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.


  • 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. 


  • 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.


  • 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.


  • 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.


  • 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. 

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