CONDITION
Brucella canis
*Brucella canis* is a bacterial infection that spreads between dogs and can affect several body systems, though it is often recognised first through problems with breeding—late pregnancy loss, weak or stillborn puppies, or difficulty conceiving. In the UK, cases have been uncommon historically, but numbers have risen since 2020, largely in dogs imported from overseas, and transmission between dogs living in the UK has now been documented. Some dogs carry the infection without showing outward signs, whilst others may develop back pain, lameness, lethargy, or swelling around the reproductive organs. *Brucella canis* is zoonotic, meaning it can pass from dogs to people, and a confirmed dog-to-human case has been documented in the UK. Detection of the infection in a dog is reportable to the Animal and Plant Health Agency (APHA) in England, Scotland and Wales, and notifiable to the Department of Agriculture, Environment and Rural Affairs (DAERA) in Northern Ireland. This page explores what patterns of change or difficulty might raise the possibility of *Brucella canis*, what is happening in the body during infection, how the diagnosis is investigated through blood tests and other means, and what approaches exist for managing the condition in individual dogs and reducing spread to other dogs and to people within households or breeding environments.
Why this matters now
Brucella canis can affect dogs at any age, though most dogs that develop signs related to the spine or joints tend to be between one and eight years old; case series of dogs with Brucella canis discospondylitis give a median age of around two and a half years, with the great majority under five. Sexually intact dogs involved in breeding activity are at higher risk of encountering the infection and showing reproductive signs, but spayed or neutered dogs can also become infected through contact with contaminated bodily fluids, and may carry the bacteria without outward signs for months or years. The infection does not appear to favour particular breeds, though medium to large dogs are represented more often in case reports, possibly reflecting the populations at higher risk of exposure.
The pattern of infection varies considerably between individuals. Some dogs develop signs within two to four weeks of exposure, whilst others may remain without obvious illness for much longer—months or even years in some cases—particularly if they are not reproductively active. Dogs that do develop signs may show problems with breeding first, or may present with joint pain, back stiffness, or lethargy that develops gradually. The infection tends to persist within the body once established, and the bacteria can continue to be shed intermittently in urine, reproductive fluids, and milk even when the dog appears well.
Signals & patterns
Early signals
Late pregnancy loss or stillbirth
A pregnant dog may lose her litter during the last few weeks of gestation, often between forty-five and fifty-five days, though loss can occur at any stage. The abortion itself may happen quietly, and the bitch may appear otherwise well.
Difficulty conceiving despite mating
A dog may fail to become pregnant after mating, or pregnancies may be reabsorbed early without visible signs. In males, reluctance to mate or reduced interest in breeding activity can sometimes be noticed.
Swelling or discomfort in reproductive organs
Male dogs may develop swelling or tenderness in the testicles, epididymis, or the area around the prostate. These changes can be subtle and may not cause obvious pain in the early stages.
Enlarged lymph nodes
Lymph nodes, particularly those that can be felt under the jaw or behind the knees, may become noticeably larger. This reflects the body's immune response and the bacteria spreading through the lymphatic system.
Lethargy or reduced appetite
Some dogs develop mild, non-specific signs such as being less active than usual, showing less interest in food, or having a dull coat. These changes can be easy to overlook or attribute to other causes.
Later signals
Back pain or stiffness
As the infection reaches the spine, a dog may show reluctance to jump, climb stairs, or turn the head and neck freely. This reflects inflammation between the vertebrae, a pattern known as discospondylitis.
Lameness or joint swelling
One or more limbs may become lame, and joints may appear swollen or warm. The lameness can shift between legs or persist in one area, depending on which joints are affected.
Eye inflammation or vision changes
Occasionally, inflammation inside the eye develops, which may be noticed as redness, cloudiness, squinting, or changes in how the dog navigates familiar spaces. This can occur in one or both eyes.
Persistent vaginal discharge after pregnancy loss
Following an abortion or stillbirth, a brownish or blood-tinged discharge may continue for weeks. This prolonged discharge can contain large numbers of bacteria.
Click to read about the biological mechanisms
How this is usually investigated
Investigation of suspected Brucella canis infection typically begins with a detailed history, particularly focusing on breeding activity, recent imports, contact with other dogs, and any pattern of reproductive failure or musculoskeletal signs. The diagnosis relies primarily on blood tests that detect antibodies or the bacteria themselves, though interpretation can be complex because infected dogs may have fluctuating antibody levels and intermittent shedding. Additional investigations may be used to assess the extent of involvement in other organs and to rule out conditions that can produce similar signs.
Brucella canis serology
Bacterial culture and sensitivity
Polymerase chain reaction (PCR)
Radiography
Complete blood count
Options & trade-offs
Management of Brucella canis infection is challenging because the bacteria persist within cells and are difficult to eliminate completely, even with prolonged treatment. Different approaches involve combinations of antibiotics, neutering, isolation measures to reduce transmission, and in some cases the decision not to pursue bacterial clearance in dogs without signs. What is workable for one household may not suit another, depending on the presence of other dogs, breeding intentions, the dog's clinical signs, and the practical realities of long-term treatment and monitoring.
Neutering and isolation without antibiotic therapy
Some owners opt to have the dog neutered to reduce shedding from reproductive tissues and to manage the dog as a permanent carrier, with strict measures to prevent transmission to other dogs. This approach accepts that the bacteria will not be cleared but focuses on reducing the risk to other animals and managing any clinical signs such as pain from discospondylitis with supportive care.
Trade-offs: The dog remains infected and may continue to shed bacteria intermittently in urine and other fluids, requiring permanent isolation from other dogs and careful handling of bodily waste, since urine, reproductive fluids and other secretions can also carry infection to people. This approach may be more practical for single-dog households or when prolonged antibiotic therapy is not feasible.
Prolonged combination antibiotic therapy
Treatment typically involves two antibiotics given together for several months—often a combination such as doxycycline with enrofloxacin, or doxycycline with an aminoglycoside initially followed by rifampicin or another agent. The aim is to reduce bacterial numbers and shedding. No antibiotic protocol has been shown to clear the infection consistently, it is not possible to confirm that a dog has eliminated it, and relapse after treatment is common. Neutering is often performed alongside antibiotic treatment to remove a major site of bacterial persistence and shedding. UK veterinary professional bodies and government guidance describe antibiotic treatment of infected dogs as a course they advise against, citing the poor and inconsistent success rate and the risk that a course of treatment creates a false impression that the infection has been cleared.
Trade-offs: Treatment is prolonged, usually a minimum of several months, and success is inconsistent; many dogs remain culture- or PCR-positive despite therapy, and relapses occur. The financial cost, need for regular monitoring blood tests, and potential for antibiotic side effects or resistance make this approach demanding for some owners. Because clearance cannot be confirmed, a treated dog is generally regarded as a possible ongoing source of infection for other dogs and for people in the household, so permanent isolation from other dogs and reduced contact with young children, older people, pregnant women and people with weakened immune systems applies whether or not antibiotics are given.
Euthanasia
In some situations—particularly in breeding kennels with multiple infected dogs, or when the risk of onward transmission cannot be adequately controlled—euthanasia may be considered to prevent further spread. This is a decision that involves weighing the individual dog's quality of life, the presence of clinical signs, the risk to other animals, and the owner's capacity to manage a persistently infected dog.
Trade-offs: This is an irreversible decision and may be difficult for owners emotionally, particularly if the dog is otherwise well. In the UK, a joint position from the main veterinary professional bodies describes assessing each positive dog individually, weighing clinical findings and test results alongside the exposure of other dogs and people, and the decision is ultimately made by the owner in discussion with their veterinary team.
Symptomatic and supportive care
For dogs with signs such as back pain or lameness from discospondylitis, pain relief with non-steroidal anti-inflammatory drugs or other analgesics, rest, and controlled activity can improve comfort. This approach may be used alongside antibiotic therapy or in dogs where bacterial clearance is not being pursued.
Trade-offs: Supportive care does not address the underlying infection and may need to be continued long-term if pain persists. Bone changes from chronic discospondylitis may continue to develop despite symptom management.
Common misconceptions
"A single negative blood test means the dog is not infected with Brucella canis."
Dogs can test negative early in infection before antibodies develop, or intermittently during chronic infection when antibody levels fluctuate. Multiple tests over time, using different methods, are often needed to confirm or exclude infection, particularly in dogs with a history of exposure or compatible clinical signs.
"Once a dog has completed a course of antibiotics and tests negative, the infection is cured."
Brucella canis is difficult to eliminate completely, and many dogs that test negative after treatment later become positive again, indicating relapse or persistent low-level infection. Long-term monitoring with repeated blood tests is needed to assess whether clearance has been sustained, and some dogs remain infected despite prolonged therapy.
"Brucella canis only affects breeding dogs, so neutered pets are not at risk."
Whilst reproductive signs are often the first clue to infection in breeding dogs, Brucella canis can infect any dog through contact with contaminated urine, saliva, nasal secretions, or other body fluids. Neutered dogs can carry and shed the bacteria, and may develop signs such as discospondylitis or lymph node enlargement without any reproductive involvement.
"Brucella canis is a dog disease and poses no risk to the people in the household."
Brucella canis is zoonotic, and a confirmed dog-to-human case has been documented in the UK. People can become infected through contact with birthing fluids, placental material, aborted or stillborn puppies, or vaginal discharge from an infected bitch. Less often, infection comes from semen, urine, blood or saliva, including when contaminated fluid is breathed in as fine droplets. UK public health assessment places the risk as very low for the general population. It is low for people with closer exposure, such as owners of infected dogs that are breeding or giving birth, breeders, and kennel and veterinary staff. Illness in people can be vague, with fever, tiredness and joint pain. Young children, people who are pregnant and people with weakened immune systems are considered more vulnerable to severe disease.
Related conditions
Brucellosis in Dogs
Brucellosis in dogs and *Brucella canis* infection describe the same condition. The former term emphasises the disease state, whilst the latter names the causative organism, but both refer to the bacterial infection that can affect reproduction, joints, and other systems.
Discospondylitis
Discospondylitis can occur as a consequence of *Brucella canis* infection when the bacterium spreads through the bloodstream and settles in the intervertebral discs and adjacent vertebrae, leading to back pain and lameness. Not all cases of discospondylitis involve *Brucella*, but the organism is recognised as one possible cause, particularly in intact breeding dogs or those with a history of import.
Bartonellosis
Bartonellosis shares certain clinical patterns with *Brucella canis*—both are bacterial infections that can spread through the bloodstream, cause intermittent lethargy or fever, and affect multiple body systems including joints and lymph nodes. Distinguishing between them often requires specific blood tests, as the visible signs can overlap in some cases.
Atypical Mycobacterial Infection
Atypical mycobacterial infection, like *Brucella canis*, can present as persistent or recurrent signs affecting lymph nodes, skin, or other tissues, and may be encountered more often in dogs with a history of import or exposure in environments where such bacteria are present. Both conditions can be slow to recognise, and diagnosis relies on identifying the specific organism through culture or molecular testing.
Gallbladder Mucocele
Gallbladder mucocele and *Brucella canis* infection are not directly linked, but both can cause non-specific signs such as lethargy, reduced appetite, and abdominal discomfort, which may prompt investigation. Imaging or blood work performed to explore such signs may reveal either condition, highlighting the importance of considering multiple organ systems when signs are vague.
Because Brucella canis can affect multiple body systems and presents differently in different dogs, understanding related patterns—such as causes of back pain, reasons for reproductive difficulty, or other infections that involve the immune system—can add useful context. The practical aspects of managing a household with an infected dog, including cleaning routines and the risk to other animals, are conversations that can evolve as the picture becomes clearer. Because Brucella canis can infect people, the household plan extends to the people in it. This applies particularly to anyone who is pregnant, very young or immunocompromised, and to anyone handling whelping, vaginal discharge or a lost litter. A positive result in a dog is reportable to APHA in England, Scotland and Wales, so public-health follow-up of human contacts can form part of the picture.
Last reviewed: 13 September 2026 · Dr Alastair Greenway MRCVS