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Canine brucellosis is a contagious bacterial infection that most often affects a dog’s reproductive system, causing infertility, pregnancy loss, and reproductive complications. However, the bacteria can also affect other organs and make spayed or neutered dogs sick. Because canine brucellosis can spread between dogs and, in rare cases, from dogs to people, early detection and prevention are critical.
In This Article
What Is Brucellosis in Dogs?
Canine brucellosis is an infectious disease most commonly caused by the bacteria Brucella canis (B. canis), says Dr. Kara Kolster, DVM DACT. Several other Brucella species exist, including Brucella suis, which commonly infects pigs, and Brucella abortus, which infects cattle and bison. Dogs can become infected with B. suis after exposure to wild pigs.
B. canis was first identified in the United States in 1966 and has since been reported worldwide. The World Organization for Animal Health considers brucellosis a priority disease because of its effects on public health, international trade, and economic activity.
It’s hard to know exactly how common canine brucellosis is in the United States. Some reports estimate infection rates among shelter dogs between 0% to 8.6%. The disease can spread when dogs move between regions with higher rates of infection, including some Southern states and parts of Central and South America.
How Does Brucellosis Spread?
Canine brucellosis spreads through contact with infected bodily fluids and reproductive tissues. Because the bacteria can survive in multiple body systems, transmission can occur in a variety of ways.
Between Dogs
Dogs can develop brucellosis through sexual transmission or, more commonly, through exposure to contaminated body fluids. Infection may occur when dogs sniff infected urine, consume contaminated milk, or come into contact with infected reproductive tissues.
The disease spreads quickly in environments where dogs live in close quarters, such as kennels or shelters. Infection can result in infertility, miscarriage, stillbirth, or reproductive failure.
Large numbers of B. canis organisms are present in semen and vaginal discharge of infected dogs, as well as the fetus, placenta, and aborted tissue.
“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,” Dr. Kolster says. “High concentrations of bacteria are also found in semen for months following infection, but lower concentrations may persist for years.”
Because of this, dogs can transmit the bacteria through natural breeding and artificial insemination, including the use of fresh or frozen semen.
Dr. Kloster adds, “Smaller quantities of B. canis are shed in urine, saliva, and nasal and eye secretions, as well as feces from intact or neutered animals.”
Transmission may also occur through inhalation, ingestion, genital contact, or exposure through wounds. In some cases, the bacteria can infect organ such as the eyes, heart, kidneys, or brain.
From Dogs to Humans
Most human cases of brucellosis are associated with consuming unpasteurized dairy products or undercooked meat contaminated with Brucella melitensis, a species more commonly linked to livestock.
While transmission from dogs to humans is uncommon, it is possible. Human infection can cause serious illness including fever, chills, enlarged lymph nodes, and an enlarged spleen.
People at higher risk include:
- Breeders
- Veterinarians
- Laboratory workers
- Kennel workers
- Pregnant individuals
- Immunocompromised individuals
- Children
Risk increases when people have direct contact with aborted fetuses, placental tissue, breeding dogs, or newborn puppies. Pet owners are generally less likely to encounter blood or vaginal discharge from an infected dog.
Symptoms of Brucellosis in Dogs
The signs of brucellosis vary depending on a dog’s sex and reproductive status. Some dogs show obvious symptoms, while others remain asymptomatic and continue spreading bacteria to other dogs.
Female Dogs
Miscarriage during the last trimester of pregnancy is one of the most common signs of brucellosis in female dogs. Abortions related to brucellosis typically occur between days 45 and 55 of pregnancy.
Other symptoms may include:
- Miscarriage late in pregnancy
- Persistent bloody or green-gray vaginal discharge
- Repeat pregnancy loss
- Infertility
- Difficulty becoming pregnant
- Stillborn puppies
- Weak newborn puppies that fail to thrive
If the infection occurs shortly after fertilization, embryos may die and be reabsorbed before pregnancy is recognized.
Male Dogs
In male dogs, brucellosis primarily affects the reproductive organs and sperm-producing structures.
Symptoms may include:
- Orchitis (painful swelling of the testicles)
- Epididymitis (inflammation of the tube that carries sperm)
- Prostatitis (inflammation of the prostate)
- Enlarged testicles
- Difficulty urinating or defecating
- Reluctance to mate
- Skin irritation from excessive licking
- Reduced semen quality
- Infertility
Recurrent infections can cause the scrotum to become hardened and shrink over time. “Semen quality is decreased after infection and many males become infertile,” Dr. Kolster notes.
Both Sexes
Not all infected dogs will develop reproductive symptoms, as some may just seem generally unwell.
Other possible signs of brucellosis include:
- Lethargy
- Weight loss
- Exercise intolerance
- Fever
- Poor coat quality
- Enlarged lymph nodes
- Eye inflammation (uveitis)
- Heart abnormalities
- Neurological problems
- Discospondylitis (a bacterial or fungal infection of the intervertebral disks and vertebral bones)
- Fatigue
- Flu-like symptoms
According to Dr. Kolster, some infected dogs never develop obvious symptoms but continue shedding bacteria and infecting other dogs.
How Veterinarians Diagnose Brucellosis
Veterinarians use laboratory testing to diagnose. Dogs with signs of a reproductive disorder should always be screened for brucellosis, even if they appear otherwise healthy.
Routine screening is especially important before breeding takes place, since infected dogs can pass the disease to mates and offspring.
Antibody Testing
The most commonly used screening tests are the rapid slide agglutination test (RSAT) and the immunofluorescence antibody (IFA) test.
According to Dr. Kolster, these tests detect antibodies against B. canis and can typically identify infections within a few weeks of exposure. Veterinarians can perform RSAT testing in the clinic, while a laboratory must run the IFA test.
These tests are highly sensitive, so they’re unlikely to miss infected dogs. However, they can produce false-positive results if a dog has been exposed to a different bacteria.
“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 with a negative B. canis test result,” notes Dr. Kolster.
Veterinarians should confirm positive screening results with more specific testing, such as agar gel immunodiffusion (AGID).
“The AGID test is only performed at a few labs and is more time-consuming, so it’s not viable as a first step in diagnosis or as a routine screening test,” she says.
Direct Detection of the Bacteria
Veterinarians can also test directly for the bacterial organism itself using PCR testing, ELISA essays, bacterial culture, or other laboratory methods.
These approaches can take longer and may produce false-negative results in some cases
“Dogs should be tested early enough to allow time for confirmatory test results prior to breeding, but not so early before a heat cycle that the dog could potentially be exposed between testing and breeding,” advises Dr. Kolster.
Veterinarians generally recommend the following testing protocols:
- Stud dogs should be tested every 6 to 12 months or more frequently if they have a high risk of infection, such as dogs in a shelter or kennel. Testing is also recommended for dogs with orchitis, epididymitis, or an unexplained drop in semen quality.
- Female dogs should be tested before each breeding and in cases of abortion or pregnancy loss
- New dogs to a kennel should be quarantined for 8 to 12 weeks and tested at the beginning and end of the quarantine period
- Dogs showing reproductive abnormalities and non-reproductive signs associated with brucellosis should be tested
- Dogs testing positive for brucellosis should be quarantined and tested, and new dogs shouldn’t be permitted
Treatment and Long-Term Management
Canine brucellosis has no cure, and treatment is often difficult. In some situations, veterinarians may recommend spaying or neutering infected dogs along with long-term antibiotic therapy rather than euthanasia. Even with treatment, dogs frequently continue shedding bacteria, especially during periods of stress.
Despite antibiotic use, B. canis can persist in lymph nodes, the spleen, the prostate, and other tissues. Because infected dogs remain a potential source of infection, breeders should never use them for breeding.
In breeding kennels with confirmed infections, veterinarians may recommend euthanasia. Dr. Kolster explains, “In some states, euthanasia or strict life-long quarantine is mandated by the health department.”
She also cautions: “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.”
If you decide against euthanasia, lifelong management typically includes sterilization, long-term monitoring, antibiotic treatment, and strict isolation protocols.
Preventing the Spread of Brucellosis
Preventing the spread of brucellosis comes down to strict hygiene, testing protocols, and isolating infected dogs.
Disinfectants such as bleach and ethanol can destroy B. canis on hard surfaces. However, the bacteria may survive on bedding, bowls, and other contaminated materials for months, especially in cool environments.
If you’re handling infected dogs, aborted tissue, or contaminated materials, always wear protective gloves, maintain good hygiene, and thoroughly disinfect areas where infected dogs have whelped.
Dogs that test positive should be isolated and monitored closely. In multi-dog households and breeding facilities, monthly testing is recommended for at least three months until all dogs test negative. Some states require positive cases to be reported to public health or animal health authorities.
Early testing, responsible breeding practices, reporting positive cases when required, and careful screening of imported or relocated dogs remain the best tools for preventing the spread of canine brucellosis.
Key Takeaways
- Canine brucellosis is a contagious bacterial disease that primarily affects the reproductive system but can impact other organs.
- The infection spreads through contact with infected reproductive tissues and bodily fluids and can occasionally infect people.
- Symptoms include infertility, miscarriage, reproductive abnormalities, lethargy, fever, and other systemic signs.
- There is no reliable cure, and infected dogs may continue to shed bacteria even after treatment.
- Routine testing, quarantine protocols, and responsible breeding practices are the most effective prevention measures.
Frequently Asked Questions
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What is canine brucellosis in dogs?
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Canine brucellosis is a bacterial infection most commonly caused by Brucella canis. It primarily affects the reproductive system, causing infertility, pregnancy loss, and breeding complications, but it can also affect other organs and body systems.
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Can canine brucellosis spread from dogs to humans?
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Yes, canine brucellosis can spread from dogs to humans, although this is uncommon. People are most at risk when handling reproductive tissues, aborted fetuses, placental material, or infected breeding animals.
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What are the most common signs of brucellosis in dogs?
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The most common signs of brucellosis in dogs include infertility, miscarriage, stillbirths, reduced semen quality, enlarged testicles, vaginal discharge, lethargy, fever, and enlarged lymph nodes.
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How is canine brucellosis diagnosed in dogs?
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Canine brucellosis is diagnosed through laboratory testing, including antibody screening tests such as RSAT and IFA, followed by confirmatory testing when needed. Additional methods may include PCR testing, bacterial culture, and other diagnostic procedures.
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Can canine brucellosis be cured?
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There is no definitive cure for canine brucellosis. Although antibiotics and sterilization may help manage infection, many dogs continue to carry and shed the bacteria, which is why long-term management and prevention are so important.