Brucellosis

The following interview was originally released as a podcast on January 23, 2014.  If you prefer to listen to the interview, the podcast is available here.

In this interview Dr. Matthew Krecic, a Diagnostics specialist for Zoetis discusses an important topic for all breeders - Brucellosis. Dr. Krecic completed his DVM at the Ohio State University, a Master’s Degree in Veterinary Science from Mississippi State University, and an MBA from the University of Florida, Warrington College of Business, and he is board-certified in small animal internal medicine through the American College of Veterinary Internal Medicine. Dr. Krecic served as a senior Telemedicine Veterinarian at IDEXX Laboratories before joining Zoetis in 2009 and continues to practice small animal internal medicine in his spare time.

AKC CANINE HEALTH FOUNDATION (CHF): Let’s start our conversation with some background on Brucellosis, can you tell us what cause the disease? Can you mention the different species?

KRECIC: Bacteria cause brucellosis, specifically Brucella canis in dogs.  Other species of Brucella bacteria exist and some of these other species (e.g. Brucella abortus and Brucella suis) have infected dogs yet infection with Brucella canis is most common to dogs; dogs are the reservoir host for Brucella canis so it remains well-established within the dog population.

CHF: Do all the different species infect dogs or is there some host specificity?

KRECIC: Yes, different species can infect dogs but host specificity predominates. 

CHF: Is Brucella canis a danger to humans?

KRECIC: Yes, it is zoonotic or can infect humans.  Handling infected canine blood, semen, or reproductive tissues can be a source of infection to humans.  Humans are susceptible to infection with other Brucella spp as a result of handling infected tissues from livestock. 

CHF: Are there any breeds of dog that are more susceptible than others?

KRECIC: Researchers have reported many purebred dogs being infected; however, I suspect the reason for this is that these breeds of dogs are routinely tested, rightly so, because of their involvement in a breeding program.  Yet, brucellosis is an equal opportunity infection; therefore, all dogs are susceptible. 

CHF: How prevalent is brucellosis among dogs?

KRECIC: Thankfully, it is not that prevalent in our well-cared for pet dog population.  I have read estimates as high as 6% of dogs in the southeastern US are affected but this percentage includes stray/feral dogs. 

CHF: How are the Brucella bacteria transmitted from dog to dog?

KRECIC: Transmission mainly occurs through natural breeding or artificial insemination (i.e. venereal) because the bacteria reside in the prostate gland and the epididymites.  Often, asymptomatic (or outwardly appearing well) infected males pass the infection through their semen to susceptible females.  However, infection may also occur through a dog’s contact with infected blood or reproductive tissues. 

CHF: What are the clinical symptoms of disease?

KRECIC: Surprisingly, many dogs do not have any clinical signs, given the significance of the disease to reproductive success.  For this reason, all dogs involved in a breeding program, again regardless of the absence of clinical signs, should be tested for the presence of brucellosis.  Clinical signs, if they do develop, are vague and non specific; they may be fever and anorexia.  I am most familiar with diagnosing this infection when the bacterial infection resides within the bloodstream (i.e. sepsis), leading to infection of the intervertebral discs called discospondylitis. 

CHF: Are there specific signs of disease in dogs or bitches?

KRECIC: Yes.  For stud dogs, some will have epididymitis, scrotal enlargement (which can be painful), and scrotal dermatitis. For bitches, some will abort within late gestation without any other clinical signs. 

CHF: Does fetal abortion always occur or can an infected bitch deliver a litter of puppies?

KRECIC: No, not always.  Some bitches deliver weak puppies.  Reportedly, some bitches that have had unsuccessful pregnancies may still deliver normally in the future.  However, these bitches may still in fact be infected. 

CHF: Does Brucellosis affect a bitch’s ability to go into heat, breed or conceive?

KRECIC: Strangely enough, Brucellosis does not affect the estrous cycle, so going into heat and breeding are unaffected.  Conception failure occasionally occurs. 

CHF: Is there any point in the course of disease that it is subclinical and the animals look or act normally?

KRECIC: Yes, most definitely.  Again, many dogs show no outward signs of infection and for this reason testing is important. 

CHF: Can Brucella be spread through shipped semen?

KRECIC: Absolutely.  Fresh chilled or even frozen semen can maintain viable Brucella canis and therefore cause infection in a female upon artificial insemination. 

CHF: Are there other infectious organisms that could cause the symptoms you described earlier, either the non-specific symptoms or the reproductive symptoms?

KRECIC: Many infections and diseases may be associated with vague clinical signs.  However, those associated with reproduction may include the protozoal infections caused by Toxoplasma gondii and Neospora caninum and the virus canine herpesvirus. 

CHF: This brings us to testing, how can breeders determine if their dog has contracted brucellosis?

KRECIC: Several tests are available through veterinarians and commercial reference laboratories.  These include rapid slide agglutination test (RSAT), agar gel immunodiffusion (AGID), and polymerase chain reaction (PCR).  Culture of the bacteria is the gold standard test. 

CHF: Can you explain what a rapid slide agglutination test, or RSAT, is and whether it is testing for the presence of the bacteria or the response of the dog’s body to the presence of bacteria?

KRECIC: This actually confuses many people so I am glad you asked.  This test identifies the presence of antibodies made to the bacteria, not the bacteria themselves.  One drop of a dog’s serum (blood collected, allowed to clot, and the clear fluid remaining is the serum) containing antibodies specific for Brucella canis combined with Brucella antigen, a piece of the bacteria, supplied with the test, agglutinates or adheres to the antigen, causing clumping that your veterinarian sees. 

CHF: How sensitive is the RSAT and how long does it take to get test results back?

KRECIC: It is quite sensitive.  The advantage of this test is veterinarians can have in-hospital results within two minutes. 

CHF: If a dog has antibodies specific for Brucella does that mean they have the infection?

KRECIC: Yes, if antibodies specific for Brucella are present, the dog has the infection, even without clinical signs. 

CHF: If a dog tests positive on the RSAT do you recommend any follow-up diagnostics?

KRECIC: The RSAT has a second step if a dog initially tests positive.  The second step involves combining two drops of the dog’s serum to two drops of another reagent contained within the test kit.  Then, this solution is combined with the Brucella antigen and clumping is once again determined within two minutes.  If clumping is seen, the dog is presumptively infected and I recommend confirming by AGID, PCR, and/or culture. 

If clumping is not seen with this second step, the dog may be early infected or not infected.  In this situation, re-test the dog in three to four weeks with the RSAT. 

CHF: Is the infection treatable with antibiotics?

KRECIC: Veterinarians prescribe antibiotics but their success at resolving the infection is doubtful because the bacteria like to hide within the dog’s cells and antibiotics are only moderately able to penetrate cells to clear all of the bacteria.  Therefore, relapses of infection are common after stopping antibiotics. 

Rather, the body’s own defenses through cell-mediated immunity are often better to clear bacteria that are within cells. 

Infected stud dogs should be removed from the breeding program and neutered to reduce the risk of infection to humans (i.e. their owners, trainers, handlers, etc.). 

Infected bitches could seemingly “recover” and deliver normal litters in the future; however, they may still in fact harbor the bacteria despite this.  Therefore, transmission to her offspring in utero is probable. 

CHF: What is current practice for managing Brucella if it is present in a kennel?

KRECIC: A brucellosis-affected kennel is a challenge to manage.  With guidance from a veterinarian, the kennel should be quarantined and infected dogs should be eliminated.  If these dogs are to be treated and/or retained as pets, they should be neutered and moved to separate housing.  Disinfect and handle dogs and their discharges/secretions, including urine, with gloved hands. 

CHF: If a breeder suspects brucellosis in their kennel who should they call?

KRECIC: Please contact your veterinarian who will properly guide your course of action. 

CHF: Are there kennel management practices that can prevent brucellosis?

KRECIC: Prevention of any infection is so much easier than managing the consequences of infection.  Brucellosis is a perfect example; simply prescribing and administering an antibiotic often does not resolve the infection, and no vaccine is available.  Pre-emptive testing is therefore best. 

Have your veterinarian test all dogs within your breeding program for brucellosis prior to every breeding and/or every 6 months, which is an ideal time for your veterinarian to also examine your dogs completely to ensure health, hopefully successful breeding, and healthy litters.  The RSAT test is a fast, easy, and economical way to screen these dogs and hopefully prevent brucellosis from affecting your kennels. 

CHF: Dr. Krecic, thank you so much for explaining brucellosis to our listeners and updating us on testing and prevention. The mission of CHF is to fund research that will improve the health of dogs, in your opinion what is our greatest gap in knowledge with respect to brucellosis and what sort of research do you think is necessary to close this gap?

KRECIC: The greatest knowledge gap is a way to stimulate the body’s own defenses through cell-mediated immunity to effectively clear Brucella canis within cells.

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