Canine brucellosis is an important cause of reproductive failure in dogs. It is most commonly caused by the bacteria Brucella canis, and results in abortion, stillbirth, orchitis and epididymitis (inflammation of the testes and epididymis), and infertility. Although the reproductive tract is the organism’s preferred site of infection, it can affect other organs and cause significant illness in spayed and neutered dogs. B. canis is also zoonotic (can be transmitted between to people) and immune-compromised individuals are most at risk.
Canine brucellosis is a reportable disease in some states but not in all, so true incidence is difficult to determine. It is widely distributed and reports range from 1% to 9% of dogs infected in the United States, with the highest incidence in the South. Relocation of dogs from the Southern to Northern US due to hurricanes and shelter capacity has resulted in geographic spread of brucellosis. Surveys of stray dogs in Central and South America report as much as 20 to 30% incidence, raising concern for widespread exposure as more dogs are imported from these areas to U.S. shelters. Cases and spread of brucellosis have been documented in dogs imported from Central & South America and Asia within the past five years. Some US states have added brucellosis testing as a requirement for transportation of dogs in an attempt to reduce the risk of spread.
- suis,which is most commonly associated with pigs, is also an emerging concern. It has been identified as the cause of canine brucellosis in dogs that were fed raw diets or exposed to wild pigs. Routine brucellosis testing in dogs does not identify B. suis, so additional testing should be done on any dog that is showing suspicious clinical signs but has a negative B. canis test result.
- canisis spread in nearly all body fluids. Bacterial concentrations are highest in the fetus, placenta and vaginal discharge associated with abortion. Organisms can be found in vaginal secretions for several weeks following an abortion, as well as in normal vaginal secretions during estrus and in milk during lactation. High concentrations of bacteria are also found in semen for months following infection, but lower concentrations may persist for years. B. canis is spread not only by natural breeding but also through fresh, chilled, and frozen semen used for artificial insemination. Smaller quantities of B. canis are shed in urine, saliva, nasal and eye secretions, as well as in feces from intact or neutered animals. Infection occurs through ingestion, inhalation, genital contact, or bite wounds.
Most brucellosis-caused abortions occur late, at approximately seven to nine weeks of gestation. Early pregnancy loss (resorption) may also occur. Occasionally, puppies will be born alive but they are generally weak and die soon after birth. Any surviving puppies are capable of transmitting brucellosis. A brucellosis-caused abortion is often followed by prolonged bloody or gray-green vaginal discharge. Exposure to aborted material and post-abortion discharge creates the highest risk for transmission of brucellosis.
Affected males commonly show acute painful swelling of the testes, epididymis and scrotum, and atrophy (shrinkage and softening) of the testes chronically. Some males will exhibit scrotal dermatitis due to licking and self-trauma. Semen quality is decreased after infection and many males become infertile.
Other signs that can occur in intact or neutered dogs include uveitis, discospondylitis (often exhibited as back pain), generalized fatigue, “flu-like” symptoms, and swollen lymph nodes. Some animals remain asymptomatic but will continue to shed the organism and infect other dogs.
Canine brucellosis should be considered in any dog exhibiting reproductive disorders. Routine screening is also vital due to the possibility of asymptomatic individuals. Because of the variety of ways in which brucellosis can be transmitted, screening should include virgin dogs and those who have only been bred via artificial insemination. Any dog that has been to a dog show, bred with chilled or frozen semen, or exposed to other dogs is potentially at risk. For example, we know of a kennel of purebred dogs infected with brucellosis by a neighboring male dog that was urine marking outside their kennel runs.
- canisis readily killed on hard surfaces by most common disinfectants (bleach, 70% ethanol, quaternary ammonium compounds). The organism can remain viable on fomites and in the environment for months, especially in cool conditions.
There is no effective treatment for brucellosis infections in dogs. Attempts have been made to treat spayed and neutered dogs with long-term antibiotics but inevitably the disease will recur, especially when the animal is stressed, and bacterial shedding will continue. A significant complicating factor is that Brucella is an intracellular organism, persisting inside a dog’s cells and often in the lymph nodes, spleen and prostate despite antibiotic therapy. The infection is a serious threat: in many cases, euthanasia may be the recommended treatment for confirmed cases of canine brucellosis in a breeding kennel. In some states, euthanasia or strict life-long quarantine is mandated by the health department. In a multi-dog household, a diagnosis of brucellosis involves testing and removing positive dogs monthly until the entire kennel tests negative for three consecutive months. Treatment of an individual dog diagnosed with brucellosis should only be attempted under the care of a knowledgeable veterinarian, with awareness of the public health risk and potential for further spread of the disease. Clearly, this disease can be devastating to our pets as well as to a breeding program.
The most common tests performed for B. canis are the rapid card agglutination test (RCAT) or the immunofluorescence antibody (IFA) test. This tests a dog’s blood for antibodies to B. canis. The RCAT test is designed to be performed in the veterinarian’s office. The IFA test is performed by most veterinary reference laboratories. Due to the significance of this disease, the RCAT & IFA tests are designed to be very sensitive. However, cross-reaction to other bacteria occurs so there is a high rate of false positive results. All positive RCAT or IFA results must be confirmed by more specific tests, such as agar gel immunodiffusion (AGID). The AGID test is only performed at a few labs and is more time-consuming, so it is not viable as a first step in diagnosis or as a routine screening test. A definitive diagnosis can be made by bacterial culture; however, B. canis is notoriously difficult to culture so this method is susceptible to false negative results. Depending on the type of test, true positive results usually can be found three or more weeks after infection. IFA tests typically provide results within 24 hours. Confirmatory testing by AGID can take five to seven days. Dogs should be tested early enough to allow time for confirmatory test results prior to breeding, if necessary, but not so early before a heat cycle that the dog could potentially be exposed between testing and breeding.
Brucellosis is most commonly spread through breeding (natural or artificial insemination) or by introduction of new animals to a kennel. Testing recommendations are as follows:
- Stud dogs should be tested every 6 to 12 months, or more frequently if at increased risk (on the show circuit, in a high-traffic kennel, or bred to untested bitches). Also, it is important to test dogs with orchitis, epididymitis, or unexplained drop in semen quality.
- Bitches should be tested prior to each breeding and in cases of abortion or pregnancy loss.
- Any new adult dogs added to the kennel should be tested and quarantined until results are confirmed.
- Any dog exhibiting suspicious reproductive abnormalities or non-reproductive signs that have been reported as consistent for with brucellosis.
Canine brucellosis has the potential to significantly impact the health of our dogs and the success of our breeding programs. Vigilance in testing, reporting positive cases to state authorities, and careful management of dogs imported from other states or countries can help prevent infection in dogs and people.