Brucellosis in Dogs

Brucellosis in dogs is a serious bacterial infection caused primarily by Brucella canis that affects the reproductive system and can spread to other organs including the spine, eyes, and lymph nodes. This disease is particularly significant because it is highly contagious among dogs, causes devastating reproductive losses including abortion and infertility, is extremely difficult to cure, and can be transmitted to humans, making it a zoonotic disease of public health concern. Understanding brucellosis is essential for dog owners, breeders, and anyone involved in canine reproduction because of its profound impact on breeding programs, the challenges of managing infected dogs, and the potential risk to human health. While canine brucellosis may be less well known than some other diseases, its consequences for affected dogs, their owners, and breeding operations can be severe.

Canine brucellosis occurs worldwide and is endemic in many regions, though prevalence varies significantly by geographic area and dog population. The disease is most commonly found in areas with large stray dog populations, limited veterinary oversight, and in breeding operations where testing protocols are not consistently followed. In the United States, brucellosis is more commonly diagnosed in southern states and in certain breeding populations. Sexually intact dogs involved in breeding are at highest risk, as the disease spreads primarily through sexual contact and exposure to infected reproductive fluids. Dogs in kennels, shelters, and breeding facilities face elevated risk due to the proximity of multiple animals and the potential for reproductive contact. While any dog can potentially become infected, the disease is rare in spayed and neutered pets with limited contact with unfamiliar dogs.

The severity of brucellosis lies in its impact on reproduction, its chronic nature, and the difficulty of achieving cure. In infected female dogs, the disease typically causes late-term abortion, stillbirth, or birth of weak puppies that often die shortly after birth, resulting in devastating losses for breeding programs. Male dogs develop reproductive tract infections causing reduced fertility and testicular abnormalities. Beyond reproductive effects, the bacteria can spread to the spine causing diskospondylitis, to the eyes causing uveitis, and to other organs causing chronic illness. Because Brucella bacteria hide inside cells where antibiotics have difficulty reaching them, infection is rarely eliminated even with prolonged treatment. Infected dogs typically remain carriers for life, capable of transmitting the disease to other dogs.

Brucellosis matters to dog owners and breeders because of its far-reaching consequences for animal and human health, breeding programs, and the practical challenges of managing infected dogs. The economic impact on breeding operations can be severe, with abortion storms potentially affecting multiple litters and infected dogs requiring removal from breeding programs. The zoonotic potential creates health risks for people who come in contact with infected dogs or their reproductive fluids, though human cases are relatively uncommon with appropriate precautions. Once a dog is diagnosed with brucellosis, difficult decisions must be made about treatment, isolation, and whether the dog can safely remain in the household. These challenges make prevention through testing and biosecurity measures far preferable to dealing with the aftermath of infection.

This comprehensive guide provides essential information about canine brucellosis for dog owners, breeders, and anyone involved in canine reproduction or rescue. You will learn about the causes of brucellosis and how it spreads, the signs and symptoms that may indicate infection, how the disease is diagnosed and the challenges of treatment, and most importantly, how to prevent infection through testing and appropriate biosecurity measures. Armed with this knowledge, you can protect your dogs and yourself from this serious disease and make informed decisions if you ever encounter an infected animal.

The primary cause of canine brucellosis is infection with the bacterium Brucella canis, a small gram-negative coccobacillus that has evolved to survive and replicate within the cells of the immune system, particularly macrophages. This intracellular location protects the bacteria from antibiotics and immune responses, allowing chronic persistent infection. The bacteria concentrate in reproductive tissues, with high levels found in semen, vaginal discharges, and aborted fetal material, facilitating spread through breeding and reproductive contact. Lower levels of bacteria may be found in urine, saliva, and other body fluids. The organism is relatively fragile in the environment, surviving only hours to days outside the host under most conditions, though it may persist longer in cool, moist, shaded environments or in biological materials like placental tissue.

Transmission of Brucella canis occurs primarily through reproductive routes, making sexually intact breeding dogs the highest risk population. Infected female dogs shed large numbers of bacteria in vaginal discharges, particularly during and after abortion or parturition, and these discharges remain highly infectious for several weeks. Male dogs excrete bacteria in their semen, transmitting infection during natural breeding or artificial insemination. Puppies can become infected in utero or through nursing, and congenitally infected puppies may not show positive blood tests until they mature. Non-reproductive transmission can occur through contact with infected urine, saliva, or nasal secretions, and potentially through mucous membrane exposure or ingestion of contaminated material, though these routes are less efficient than reproductive transmission.

Genetic factors do not appear to play a significant role in susceptibility to brucellosis, as all dogs are considered susceptible to infection regardless of breed. However, certain breeds may be overrepresented in diagnostic statistics simply because they are more commonly used for breeding and therefore more frequently tested. There is no evidence of genetic resistance or enhanced susceptibility to Brucella canis in any dog breed. Once exposed to sufficient numbers of bacteria through an appropriate route, any dog can become infected. Individual variation in immune response may affect the severity of clinical signs, but even dogs that appear healthy after infection typically remain chronically infected and capable of transmitting the disease.

Environmental factors influence transmission risk primarily through their effect on dog population dynamics and opportunities for contact between infected and susceptible animals. Areas with large populations of free-roaming unsterilized dogs have higher brucellosis prevalence because these dogs have more opportunities for reproductive contact with infected animals. Kennels, breeding facilities, and shelters where multiple intact dogs are housed in proximity create conditions favorable for disease spread. Environments where biosecurity is lax, testing is inconsistent, and new animals are introduced without quarantine and testing face elevated risk of introducing brucellosis. Geographic regions with warmer climates may support slightly longer environmental survival of the organism, though this effect is modest compared to the importance of direct animal contact.

Age and reproductive status are important risk factors for brucellosis exposure and clinical disease. Sexually mature, intact dogs involved in breeding face the highest risk because of the reproductive route of transmission. Puppies born to infected mothers may be infected congenitally but often test negative until they reach sexual maturity, when hormonal changes may trigger increased bacterial shedding and positive test results. Young dogs being introduced into breeding programs for the first time may be exposed to infected animals if pre-breeding testing is not performed. Older breeding dogs that have had multiple partners over their careers have cumulative exposure risk. Spayed and neutered dogs that do not engage in breeding have dramatically reduced risk, though infection through non-reproductive routes remains possible.

Other risk factors for canine brucellosis include source of acquisition, biosecurity practices, and human behavior that influences disease transmission dynamics. Dogs acquired from sources where brucellosis testing is not standard practice, including some commercial breeders, pet stores, auctions, and rescue organizations importing dogs from endemic areas, may carry undetected infection. Breeding operations that do not require testing before breeding, that use outside studs or accept outside dogs for breeding without testing, or that fail to isolate and test new arrivals before introduction to the resident population are at elevated risk. International dog importation has introduced brucellosis to areas and populations where it was previously rare. Artificial insemination using untested semen can spread infection without direct contact between dogs.

Early warning signs of brucellosis may be absent or extremely subtle, making the disease particularly insidious because infected dogs often appear completely healthy while actively shedding bacteria and transmitting infection. In breeding animals, the first indication of brucellosis in a kennel is often reproductive failure, with one or more females experiencing unexpected pregnancy loss. Dogs may appear slightly lethargic or have mildly enlarged lymph nodes, but these signs are easily overlooked. Male dogs may show subtle testicular changes that progress so gradually they go unnoticed until significant damage has occurred. Because the early disease often produces no obvious symptoms, routine testing is the only reliable way to detect infection before it spreads and causes losses.

Common reproductive symptoms of brucellosis are the hallmark presentation of this disease. In female dogs, the classic sign is abortion during the last trimester of pregnancy, typically between 45 and 59 days of gestation. Aborted puppies may appear normal but dead, or may be partially resorbed. Live puppies born to infected mothers are often weak and may die within hours to days of birth. Some females experience early embryonic death and resorption, which may appear as failure to conceive rather than abortion. Vaginal discharge, which may be brownish or greenish and persist for weeks after abortion, is highly infectious. Male dogs develop epididymitis and orchitis, inflammation of the epididymis and testicles that causes swelling, pain, and eventually testicular atrophy and decreased fertility. Infected males may have abnormal sperm and reduced sperm counts, contributing to apparent infertility.

Behavioral changes in dogs with brucellosis are typically subtle and nonspecific. Infected dogs may show mild lethargy or reduced activity, though many appear completely normal. Dogs with diskospondylitis, a spinal infection that can result from brucellosis, may show back pain, reluctance to jump or climb, stiffness, or in severe cases, weakness or paralysis of the limbs. Eye involvement causing uveitis may produce behavioral signs including squinting, light sensitivity, or rubbing at the affected eye. Dogs experiencing reproductive complications may show nesting behavior, restlessness, or signs of impending whelping followed by the birth of dead or dying puppies. Overall, behavioral changes are rarely dramatic enough to prompt veterinary attention in the absence of obvious reproductive problems.

Physical signs of brucellosis include both reproductive tract abnormalities and systemic manifestations. Enlargement of lymph nodes, particularly those in the inguinal and submandibular regions, may be palpable. Male dogs may have enlarged, painful testicles in acute orchitis, followed by testicular atrophy as the disease progresses. Scrotal dermatitis, inflammation and skin changes of the scrotum, may develop. Female dogs may have prolonged vaginal discharge following pregnancy loss. Dogs with diskospondylitis may have an arched back or painful response to spinal palpation. Ocular examination in dogs with uveitis may reveal redness, cloudiness, or other abnormalities of the eye. Weight loss and poor body condition may develop in dogs with chronic infection, though many infected dogs maintain good body condition indefinitely.

Progression of brucellosis symptoms in dogs typically follows a pattern of initial reproductive failure followed by potential spread to other organ systems. After initial infection, bacteria disseminate through the bloodstream to reproductive organs where they establish persistent infection. The first clinical signs usually involve reproductive failure occurring within weeks to months of infection. In males, testicular changes progress from acute inflammation to chronic atrophy over months. Bacterial spread to the spine, eyes, or other organs can occur months to years after initial infection, though many dogs never develop these complications. Lymph node enlargement may persist indefinitely. The chronic carrier state, in which dogs remain infected and potentially infectious while appearing healthy, can last for years. Emergency signs requiring immediate attention include signs of systemic illness such as high fever, collapse, or severe debilitation, acute severe back pain suggesting diskospondylitis with possible spinal cord compression, or sudden blindness or severe ocular pain.

Veterinary examination for suspected brucellosis begins with a thorough history, particularly regarding breeding activities, reproductive failures, and potential exposure to infected dogs. The veterinarian will ask about the source of the dog, any breeding history, recent pregnancies or abortions, and whether any dogs the patient has been bred to have been diagnosed with brucellosis. Physical examination includes careful palpation of lymph nodes, examination of the reproductive tract including testicular palpation in males, assessment for spinal pain, and ophthalmic examination if eye involvement is suspected. Based on history and examination findings, the veterinarian will recommend appropriate diagnostic testing. In breeding dogs, testing is often recommended even in the absence of clinical signs as a routine biosecurity measure.

Diagnostic testing for brucellosis involves serological tests that detect antibodies to Brucella canis, and in some cases, tests that detect the bacteria themselves. Screening tests including the rapid slide agglutination test (RSAT) and tube agglutination test (TAT) detect antibodies and are commonly used for initial screening, though they can produce false positive results. Positive screening tests should always be confirmed with more specific testing such as the agar gel immunodiffusion (AGID) test, which is more specific but may produce false negatives in early infection. Blood culture can definitively confirm active infection by growing the organism, but may be negative even in infected dogs due to intermittent bacteremia. PCR testing can detect bacterial DNA in blood or tissues. Because no single test is perfect, diagnosis often requires a combination of tests and may need to be repeated over time. Testing dogs before breeding and quarantining and testing new animals before introduction to a kennel are essential biosecurity measures.

Treatment of canine brucellosis is challenging and controversial because the infection is extremely difficult to eliminate. Antibiotic protocols using combinations of drugs such as doxycycline, enrofloxacin, streptomycin, or gentamicin have been used, typically administered for extended periods of four to six weeks or longer. Even with aggressive treatment, cure rates are disappointing, with many dogs remaining chronically infected despite apparent clinical improvement. Neutering infected dogs is strongly recommended as it removes the reproductive organs where bacteria concentrate, reduces shedding, and prevents reproductive transmission. However, neutering does not eliminate infection, and neutered dogs may continue to shed bacteria in urine and other secretions at lower levels. Some authorities recommend euthanasia of infected dogs as the only way to definitively eliminate infection and prevent transmission, particularly for dogs that cannot be reliably isolated from other dogs and humans.

Home care for dogs diagnosed with brucellosis focuses on preventing transmission to other dogs and humans while managing any clinical signs present. Infected dogs should be isolated from other dogs, particularly intact dogs and those in breeding programs. Because brucellosis can be transmitted to humans, particularly through contact with reproductive fluids, aborted material, or urine, appropriate precautions are essential. Wearing gloves when handling the infected dog or cleaning up after them, avoiding contact with reproductive discharges, thoroughly washing hands after any contact, and informing anyone who has regular contact with the dog about the infection are important measures. Pregnant women and immunocompromised individuals should avoid contact with infected dogs. Regular veterinary monitoring allows assessment of the dog's condition and repeated testing to evaluate infection status.

Prognosis and long-term outcomes for dogs with brucellosis are guarded because true cure is rare. Most infected dogs remain chronically infected for life, even with treatment and neutering. Clinical signs may resolve with treatment, and dogs may appear healthy while still harboring bacteria. Infected dogs that are not euthanized require lifelong management to prevent transmission. Dogs with complications such as diskospondylitis or severe ocular involvement may have permanent damage to affected organs. The emotional and practical burden on owners of infected dogs is significant, as decisions must be made about whether the dog can safely remain in the household, particularly if there are other dogs or high-risk humans present. For breeding operations, diagnosis of brucellosis may necessitate depopulation or extensive testing and culling programs with significant economic impact.

Cost considerations for brucellosis diagnosis and management can be substantial and ongoing. Initial testing may cost fifty to two hundred dollars depending on the tests performed. Confirmatory testing following positive screening adds additional expense. Treatment with prolonged antibiotic courses may cost several hundred dollars, and neutering surgery adds further expense. Ongoing monitoring with repeat testing adds cumulative costs over time. The indirect costs of the disease, including lost breeding potential, potential exposure of other animals, and liability concerns, may far exceed direct medical costs. For breeding operations, the economic impact of brucellosis can be devastating, with losses from aborted litters, removal of infected dogs from breeding programs, required testing of all exposed animals, and potential loss of reputation.

Prevention of brucellosis through testing and biosecurity is far more effective than attempting to manage the disease after infection occurs. All dogs should be tested for brucellosis before breeding, regardless of whether they have been tested previously, as infection can occur at any time. Both the male and female should have negative tests within the month before breeding takes place. Reputable breeders maintain documented testing records and require proof of negative status before allowing any breeding. Dogs being introduced to a household or kennel with other dogs, particularly intact dogs, should be quarantined and tested before introduction. Animals acquired from shelters, rescues, or sources where testing history is unknown should be tested before contact with resident dogs. Artificial insemination should only be performed using semen from tested negative males.

Lifestyle modifications for managing brucellosis risk focus on limiting exposure to potentially infected dogs and maintaining closed breeding populations where possible. Operating a closed kennel where outside dogs are not brought in for breeding significantly reduces introduction risk. When outside animals must be used, requiring documentation of negative testing, repeating testing, and maintaining quarantine periods before breeding provides layers of protection. Avoiding acquisition of dogs from high-risk sources including auctions, pet stores, and international imports reduces risk of introducing infected animals. For pet dogs, spaying and neutering eliminates the reproductive route of transmission and dramatically reduces risk even if exposure occurs. Avoiding contact with stray dogs and dogs of unknown health status provides additional protection.

Regular monitoring and testing protocols are essential components of brucellosis prevention for breeding operations. Annual testing of all breeding animals provides baseline health information and may detect infections before they spread. Testing after any reproductive failure, including apparent failure to conceive, early embryonic loss, and abortion, may reveal the cause of the problem. New animals should be tested immediately upon arrival, again after a quarantine period, and potentially a third time before being considered clear for integration. Testing both before and after breeding provides additional assurance. Keeping detailed records of all test results, breeding activities, and animal movements facilitates tracking if an infection is detected. Working with a veterinarian experienced in canine reproduction to develop appropriate testing protocols for your specific situation optimizes protection.

Long-term management for kennels or households where brucellosis has been diagnosed requires comprehensive response to eliminate the infection and prevent recurrence. All dogs in the facility should be tested, with positive dogs isolated or removed. Depending on the extent of infection and the goals of the operation, options range from treating and isolating infected dogs to removing all infected animals through euthanasia or placement in appropriate pet homes. Premises should be thoroughly cleaned and disinfected, though the organism is relatively susceptible to common disinfectants. A waiting period before repopulating with tested negative animals reduces risk of residual environmental contamination. Investigating the source of introduction helps prevent recurrence. Developing stricter biosecurity protocols going forward provides protection against future outbreaks.

Support resources for managing brucellosis include veterinary professionals with expertise in infectious disease and reproduction, as well as regulatory authorities. Your veterinarian can provide guidance on testing protocols, treatment options, and biosecurity measures appropriate for your situation. Veterinary specialists in theriogenology (reproduction) have extensive experience with brucellosis in breeding populations. Veterinary diagnostic laboratories perform the specialized testing needed for accurate diagnosis. State veterinarians and animal health officials may need to be notified of positive cases in some jurisdictions and can provide guidance on regulatory requirements. Because brucellosis is a zoonotic disease, human health authorities may be involved when human exposure is a concern. Support groups and educational resources for breeders provide information on best practices for prevention and management.

Emergency signs related to brucellosis that require immediate veterinary attention include signs of active abortion such as vaginal discharge with fetal material, which creates a highly infectious situation requiring appropriate containment and professional handling. A dog in active labor with obvious distress and no puppies delivered, or delivering only dead puppies, needs urgent evaluation. Signs of severe systemic illness including high fever, collapse, or severe debilitation in any dog, whether or not brucellosis is suspected, require emergency care. Acute onset of severe back pain with weakness or paralysis of the limbs suggests possible spinal involvement that may constitute a medical emergency. Sudden blindness or severe eye pain requires immediate evaluation to prevent permanent damage.

Urgent signs warranting a same-day or next-day veterinary appointment include unexpected pregnancy loss at any stage, which should prompt investigation including brucellosis testing. Discovery that a dog your pet has been bred to has tested positive for brucellosis requires immediate testing and isolation of your dog. Male dogs showing testicular swelling, pain, or rapidly developing asymmetry should be evaluated promptly. Dogs showing signs consistent with diskospondylitis including back pain, reluctance to move, or stiffness should be examined soon. Any dog in a known exposed population that develops symptoms suggestive of brucellosis warrants prompt evaluation.

Routine veterinary consultation is appropriate for scheduling pre-breeding testing, which should be performed within thirty days before any planned breeding. New dogs being introduced to a household or kennel should be tested during their quarantine period. Annual wellness examinations for breeding dogs should include discussion of brucellosis testing protocols. If you are planning to acquire a dog for breeding purposes, consulting with your veterinarian about appropriate testing requirements before purchase provides protection. Dogs that have been bred to animals of unknown or questionable health status should be tested. Questions about brucellosis prevention, testing protocols, or biosecurity measures for breeding programs can be addressed during routine consultations.

Trust your judgment when evaluating potential brucellosis concerns and err on the side of caution given the serious consequences of this disease. If you have any concern that your dog may have been exposed to brucellosis, testing is appropriate regardless of whether symptoms are present. Remember that many infected dogs appear completely healthy, so absence of symptoms does not rule out infection. If you are involved in breeding dogs, establishing a relationship with a veterinarian experienced in canine reproduction who can guide appropriate testing and prevention protocols is invaluable. The consequences of brucellosis for individual dogs, breeding programs, and human health are serious enough to warrant thorough precautions. When in doubt about exposure, symptoms, or testing needs, seek professional guidance.