Brucellosis in Dogs: Symptoms, Diagnosis, Treatment, and Breeder Guide
This article is reviewed for clinical accuracy. Always consult your veterinarian for diagnosis and treatment.
Key Takeaways
- Canine brucellosis is caused by Brucella canis, a gram-negative, non-motile, non-spore-forming intracellular coccobacillus that preferentially survives and replicates within macrophages and other mononuclear phagocytic cells after being phagocytosed at the initial site of infection; the organism’s intracellular lifestyle is the fundamental reason why brucellosis is so difficult to treat with antibiotics: most antibiotics do not achieve bactericidal concentrations inside macrophages, and drugs that do (tetracyclines, fluoroquinolones, rifampin) must be used in combination over prolonged treatment periods to have any chance of eradicating intracellular organisms; Brucella canis belongs to the same genus as the animal-to-human pathogens B. abortus (cattle), B. melitensis (goats and sheep), and B. suis (pigs), but is less virulent in humans than these species; nevertheless, B. canis is a confirmed zoonotic pathogen and human infections from dog exposure, while uncommon, do occur and can cause significant illness including febrile bacteremia, endocarditis, discospondylitis, and uveitis.
- The primary route of Brucella canis transmission between dogs is sexual contact: infected males shed enormous quantities of B. canis in their semen (concentrations of 10 to the 7th to 10 to the 9th organisms per milliliter of ejaculate) for weeks to months during the bacteremic phase, and infected females shed the organism in vaginal secretions and especially in the massive quantities of infected material associated with abortion; the aborted fetal tissues, placental membranes, and uterine discharge from a Brucella-infected bitch aborting between days 45 and 55 of gestation represent the highest-concentration source of B. canis in any clinical setting; other dogs in the environment that are exposed to aborted material through direct contact, sniffing, or oral exposure face very high risk of infection; other transmission routes include contact with urine (males shed B. canis in urine for months), milk (lactating infected bitches can transmit to nursing puppies), and oronasal contact with infected secretions; the oral-nasal mucosa is an efficient entry route because Brucella efficiently colonizes lymphoid tissue in the oropharynx before disseminating hematogenously.
- In intact female dogs, brucellosis classically presents as late-term abortion (gestational day 45 to 55) of apparently normal-appearing but dead fetuses; this is distinguished from early fetal death and resorption (which occurs in early gestation without visible abortion) and from other causes of late-term abortion (canine herpesvirus, Toxoplasma gondii, canine distemper); the characteristic feature of Brucella abortion is that the fetuses appear morphologically normal (normal size and development for gestational age) but are dead at delivery, in contrast to the macerated, autolyzed fetuses seen with bacterial uterine infection or some viral abortions; vaginal discharge before and after the abortion event is a grey-green to brown viscous fluid that contains extremely high concentrations of B. canis; some bitches fail to conceive at all (early embryonic death and resorption without visible abortion), have reduced litter sizes, or experience a series of failed breeding attempts before brucellosis is suspected and tested; generalized lymphadenopathy (inguinal, submandibular, and prescapular lymph nodes) is present in many clinically affected dogs and reflects the systemic lymphoreticular involvement during the bacteremic phase.
- In intact male dogs, brucellosis most consistently produces epididymitis, which manifests as scrotal swelling and pain; the epididymis (the elongated structure attached to the dorsal surface of the testicle that stores and transports sperm) becomes enlarged, firm, and painful; the associated testicle may show orchitis (testicular inflammation) with scrotal skin erythema, edema, and dermatitis from the male licking the irritated scrotum; in chronic infection, the inflammatory response is replaced by fibrosis and the testicle atrophies, producing characteristic small, firm, irregularly contoured testes on palpation; testicular atrophy in a young male dog in a breeding program is a red flag for chronic brucellosis; sperm abnormalities (head-to-head agglutination, detached heads, abnormal acrosomes) appear early in the course of male brucellosis and contribute to infertility; the semen abnormalities typically precede the gross structural changes of epididymitis by several weeks; prostatitis is a common concurrent finding in infected males; discospondylitis and uveitis can occur in both sexes as complications of bacteremia.
- The diagnosis of canine brucellosis is complicated by the imperfect performance of all available screening and confirmatory tests; the rapid slide agglutination test (RSAT) is the most widely available in-clinic screening test and has high sensitivity (approximately 95 to 99 percent for active bacteremic infection) but has a false-positive rate of 30 to 50 percent in some studies due to cross-reactivity between B. canis LPS antigens and antigens from other gram-negative bacteria (Pseudomonas fluorescens, Bordetella bronchiseptica, and others); every positive RSAT result therefore requires confirmatory testing before a diagnosis is communicated to the owner; the 2-mercaptoethanol RSAT (2ME-RSAT) or agar gel immunodiffusion (AGID) with internal protein antigen (cytoplasmic protein antigen, CPA-AGID) are used as confirmatory tests and have substantially better specificity than the RSAT; blood culture (requiring 7 to 21 days incubation in specialized broth, performed at a biosafety level 2 or 3 laboratory because B. canis is a biosafety hazard) is the definitive diagnostic gold standard; PCR on blood, semen, or reproductive secretions has excellent sensitivity and specificity and is available at reference laboratories.
- Management of a Brucella-positive dog in a breeding program involves three simultaneous considerations that must be addressed together rather than sequentially: treatment of the infected dog (with the honest acknowledgment that microbiological cure is not reliably achievable with antibiotics), reproductive management (neutering eliminates the primary bacterial reservoir and the primary route of transmission, and is strongly recommended for confirmed-positive dogs), and quarantine and testing of all other dogs in the same household or kennel (all in-contact intact dogs should be tested and any positive dogs removed from contact with negative dogs and with humans during the infectious period); in kennels, B. canis spreads silently because most infected dogs show minimal systemic illness and continue to shed organism in reproductive secretions; a single undetected infected male or female in a breeding program can infect every dog mated over months before the diagnosis is made; routine pre-breeding testing of every dog before each breeding is the standard of care in responsible breeding programs.
The German Shorthaired Pointer kennel had produced three successful litters from the same stud dog over the previous year. In late October, the first bitch from that year’s breeding season aborted three apparently normal-appearing male fetuses at day 51 of gestation; the fetuses were correctly developed for gestational age but stillborn, and a grey-green vaginal discharge persisted for 10 days. Three weeks later, a second bitch from the same kennel aborted at day 49. The kennel owner consulted a veterinarian, who performed an RSAT on both bitches and the stud dog; all three dogs were RSAT-positive. The RSAT positives were confirmed with CPA-AGID serology, which was positive in all three dogs. Blood culture grew Brucella canis from the stud dog after 12 days incubation. The veterinarian notified the state animal health laboratory (B. canis is reportable in many states) and counseled the kennel owner on the options: the stud dog and both bitches were neutered; all five remaining intact dogs in the kennel were tested; two additional RSAT-positive dogs were found and confirmed; the kennel was quarantined, all positive dogs were neutered and placed on doxycycline plus enrofloxacin therapy, and the kennel’s breeding program was suspended for 6 months while serial testing confirmed that the remaining negative dogs stayed negative.
The Organism: Intracellular Bacterium of Breeding Dogs
| Feature | Brucella canis | Other Brucella Species of Note |
|---|---|---|
| Primary host | Domestic dogs (Canis lupus familiaris); also found in wild canids (coyotes, wolves, foxes) | B. abortus: cattle; B. melitensis: goats and sheep (most virulent in humans); B. suis: pigs; B. ovis: sheep (not zoonotic) |
| Human virulence | Low to moderate; B. canis causes self-limiting febrile illness in most immunocompetent humans; rare cases of endocarditis, discospondylitis, uveitis; overall human disease burden from B. canis is low in the US | B. melitensis is the most virulent human pathogen in the genus; B. abortus and B. suis also cause serious human brucellosis; all three are Tier 1 Select Agents (bioterrorism classification) |
| Biosafety classification | Biosafety Level 2 for standard diagnostic work; culture requires BSL-2 or BSL-3 laboratory conditions; laboratory-acquired infections are documented | B. abortus, B. melitensis, and B. suis are Tier 1 Select Agents requiring BSL-3 containment and registration |
| Lipopolysaccharide (LPS) type | Rough LPS (lacks the O-polysaccharide side chain present on smooth Brucella species); this rough LPS is less immunogenic than smooth LPS and accounts for some of the serological cross-reactivity problems with the RSAT | B. abortus, B. melitensis, and B. suis have smooth LPS with the O-polysaccharide chain; serological tests designed for these species (Rose Bengal test, serum agglutination test) are insensitive for B. canis |
| Primary tissue tropism | Trophoblast cells of the placenta, epididymal epithelium, prostate, uterine endometrium, lymph nodes, spleen, macrophages throughout the mononuclear phagocyte system; intervertebral disc spaces (discospondylitis) | Similar reproductive tract tropism for B. abortus and B. melitensis; all Brucella species preferentially infect cells with high erythritol concentrations (placenta, testicle, epididymis) in their natural hosts |
| Antibiotic susceptibility | Susceptible in vitro to tetracyclines (doxycycline), fluoroquinolones (enrofloxacin, ciprofloxacin), aminoglycosides (streptomycin, gentamicin), rifampin, and trimethoprim-sulfamethoxazole; in vivo cure is difficult to achieve due to intracellular sequestration; combination therapy required; resistance to penicillins and cephalosporins is intrinsic | Similar susceptibility profile; human treatment protocols use doxycycline plus rifampin or doxycycline plus streptomycin for 6 weeks minimum |
Transmission Routes and Risk Factors
| Transmission Route | Organism Concentration | Risk Level |
|---|---|---|
| Mating with infected male: vaginal mucosa exposure to infected semen | 10 to the 7th to 10 to the 9th organisms/mL ejaculate during active bacteremia | Very high; the primary route of spread in breeding programs |
| Contact with aborted fetal material, placental membranes, uterine discharge | 10 to the 8th to 10 to the 10th organisms/mL aborted material; highest concentration source in clinical settings | Very high; any dog or human in contact with abortion material faces substantial exposure |
| Vaginal secretions from infected bitch (non-abortion) | Variable; highest around estrus and parturition | Moderate to high |
| Urine from infected male | 10 to the 3rd to 10 to the 5th organisms/mL urine; shed for months during bacteremia | Moderate; contaminated environment is a source for in-contact dogs |
| Milk from infected lactating bitch | Variable; significant enough to infect nursing puppies | Moderate for nursing puppies |
| Saliva, nasal secretions | Low concentrations; occasional shedding during bacteremia | Low; casual contact is a low-risk route |
| Indirect contact (contaminated kennel surfaces, bedding, food bowls) | Variable; B. canis survives days to weeks in moist environments | Low to moderate in contaminated environments; regular disinfection with quaternary ammonium compounds or dilute bleach is effective |
Clinical Signs by Sex and Reproductive Status
Intact Females
The hallmark clinical sign of brucellosis in intact females is late-term abortion, occurring most commonly between gestational days 45 and 55 (the second half of a normal 63-day gestation); the aborted fetuses appear morphologically normal for their gestational age but are dead at delivery; a small percentage of fetuses delivered alive in a Brucella-affected litter are weak and die within a few days of birth; the vaginal discharge associated with Brucella abortion is grey-green to brown, viscous, and may persist for up to 3 to 6 weeks after the abortion event; some infected bitches do not abort recognizable fetuses but instead have early embryonic death and resorption, resulting in smaller than expected litter sizes or complete failure to conceive despite documented mating during estrus; a bitch that repeatedly fails to produce a live litter or produces progressively smaller litters over consecutive breeding seasons should be tested for brucellosis as a priority; generalized lymphadenopathy is a consistent finding during active bacteremia and is present in most clinically affected dogs whether or not overt reproductive failure has occurred; the lymph nodes most prominently enlarged are the submandibular, prescapular, and inguinal nodes.
Intact Males
Epididymitis is the most consistent and diagnostically informative clinical sign in intact males with brucellosis; the epididymis becomes enlarged, firm, and tender, most often affecting the tail of the epididymis (cauda epididymis) first; the affected testicle shows concurrent orchitis with heat, pain, and scrotal skin changes (erythema, edema, hyperpigmentation from chronic licking); in the acute phase the scrotum is swollen, warm, and the dog may walk with a wide-based hindlimb stance to avoid scrotal contact; in chronic infection the inflammatory response is replaced by fibrosis, the epididymis becomes scarred and indurated, and the testicular parenchyma undergoes immune-mediated damage resulting in testicular atrophy; bilateral testicular atrophy with small, firm, irregular testes in a previously fertile breeding male is a strong indicator of chronic brucellosis even in the absence of current systemic signs; scrotal dermatitis from persistent licking is a common associated finding; seminal abnormalities (head-to-head sperm agglutination, detached sperm heads, acrosomal abnormalities, teratospermia) are detectable on semen evaluation before gross structural changes are apparent and are a sensitive early indicator of Brucella epididymitis; the prostatic gland is consistently infected in bacteremic males and may show enlargement or abscessation in severe cases.
Systemic Complications in Both Sexes
Discospondylitis (intervertebral disc space infection with endplate erosion) from hematogenous Brucella seeding of the disc space is the most important non-reproductive complication of canine brucellosis; spinal pain, reluctance to move, and progressive neurological signs (paresis, ataxia, urinary dysfunction) develop as the infection erodes vertebral endplates and compresses the spinal cord; Brucella canis is among the most common bacterial causes of discospondylitis in dogs and should be included in the differential diagnosis of any intact dog with disc space infection; uveitis (anterior or posterior) occurs in some dogs during or after bacteremia and can cause vision impairment; the eye lesion reflects direct Brucella invasion of uveal tissue or immune complex deposition during the bacteremic phase; meningoencephalitis is a rare but serious complication reported in some cases of persistent bacteremia.
Diagnosis
Rapid Slide Agglutination Test (RSAT)
The RSAT is the most commonly available in-clinic screening test for B. canis in North America and detects IgG antibodies against B. canis LPS antigen; it is performed by mixing a drop of patient serum with a suspension of stained B. canis antigen on a glass slide and observing for macroscopic agglutination within 30 seconds to 2 minutes; sensitivity for active bacteremic infection is approximately 95 to 99 percent, making it an excellent rule-out test (a negative RSAT in a dog without concurrent immunosuppression has high negative predictive value); the critical limitation of the RSAT is its specificity: false-positive rates of 30 to 50 percent have been reported in various studies, primarily due to cross-reactive antibodies against LPS antigens of other gram-negative bacteria (Bordetella bronchiseptica, Pseudomonas fluorescens, Staphylococcus epidermidis) that are common colonizers of the canine respiratory and gastrointestinal tracts; a positive RSAT result therefore requires confirmatory testing with a more specific test before a diagnosis is communicated to the owner; communicating an unconfirmed RSAT positive as a confirmed B. canis diagnosis can lead to unnecessary euthanasia of Brucella-negative dogs.
Confirmatory Tests
The 2-mercaptoethanol rapid slide agglutination test (2ME-RSAT) reduces false-positive results by treating the serum with 2-mercaptoethanol before testing, which destroys IgM antibodies and leaves only IgG; because many false-positive reactions in the standard RSAT are mediated by IgM against cross-reactive LPS antigens, the 2ME-RSAT has substantially improved specificity while maintaining sensitivity; the agar gel immunodiffusion (AGID) test using cytoplasmic protein antigen (CPA-AGID) detects antibodies against Brucella internal protein antigens (rather than LPS), which do not cross-react with other gram-negative bacteria and therefore have specificity above 95 percent; the CPA-AGID is considered one of the most specific serological tests for B. canis and is the preferred confirmatory test in most veterinary reference laboratory panels; blood culture is the definitive gold standard (positive culture confirms active bacteremia) but requires 7 to 21 days for B. canis to grow in specialized broth cultures (BACTEC blood culture system or similar), must be performed in a BSL-2 laboratory with trained personnel using appropriate biosafety precautions, and has variable sensitivity because bacteremia is intermittent; PCR on EDTA blood, semen, or reproductive secretions provides rapid, sensitive, and specific results and is available at reference laboratories.
Interpreting the Diagnostic Algorithm
The recommended diagnostic approach for screening in a breeding program is:
- RSAT (or 2ME-RSAT) as the initial screening test; a negative result in a dog without immunosuppression effectively rules out active brucellosis
- Any positive RSAT result is confirmed with CPA-AGID serology; dogs that are RSAT-positive but CPA-AGID-negative are most likely false positives and do not have brucellosis
- Dogs that are positive on both RSAT and CPA-AGID are considered presumptively positive; blood culture and/or PCR confirms the diagnosis and provides material for culture
- Dogs with compatible clinical signs (epididymitis, late-term abortion, discospondylitis) and a positive CPA-AGID are considered confirmed brucellosis regardless of blood culture result because bacteremia is intermittent
Treatment and Management
Antibiotic Therapy
No antibiotic protocol has been shown to reliably achieve microbiological cure (complete elimination of B. canis from the body) in dogs; this is the most important clinical reality of canine brucellosis management; the intracellular location of B. canis within macrophages and reproductive tract cells protects the organism from most antibiotics, and treatment can reduce bacteremia and clinical signs without eliminating the intracellular reservoir; the most commonly used protocols are:
- Doxycycline plus enrofloxacin: Doxycycline at 10 mg/kg orally once daily combined with enrofloxacin at 5 mg/kg orally once daily for 4 to 8 weeks; doxycycline achieves moderate intracellular concentrations; enrofloxacin achieves excellent intracellular concentrations in macrophages; this combination reduces bacteremia and clinical signs in most treated dogs but relapse is common after treatment is stopped; this combination is now more commonly used than the historical doxycycline plus streptomycin protocol because enrofloxacin avoids the nephrotoxic risk of streptomycin
- Doxycycline plus rifampin: Doxycycline at 10 mg/kg orally once daily combined with rifampin at 5 mg/kg orally once daily for 4 to 8 weeks; rifampin achieves excellent intracellular concentrations and has synergistic activity with doxycycline against Brucella; hepatotoxicity with rifampin requires monthly liver enzyme monitoring; rifampin can cause orange discoloration of urine and tears (inform owners)
- Extended-duration protocols: Some veterinary infectious disease specialists recommend two courses of combination antibiotics separated by a 2-week rest period, or continuous combination therapy for 12 weeks; there is no evidence that extended treatment reliably achieves microbiological cure, but it may prolong remission
All antibiotic therapy for brucellosis should be combined with neutering (spaying or castrating) because the reproductive tract is the primary bacterial reservoir and removing it substantially reduces the bacterial burden; antibiotic therapy without neutering is less effective and the dog remains a higher infection risk for in-contact dogs and humans during and after treatment.
Neutering
Neutering (spaying for females, castration for males) is strongly recommended for all confirmed-positive dogs for three reasons: it removes the primary anatomical reservoir of B. canis (the uterus, ovaries, testicles, epididymides, and prostate), it eliminates or substantially reduces shedding in reproductive secretions (the primary transmission route), and it prevents further use of the dog in a breeding program (which would be irresponsible with a Brucella-positive dog regardless of antibiotic treatment status); neutering does not cure brucellosis by itself because B. canis persists in the macrophages and lymph nodes of neutered dogs, but it substantially reduces organism shedding and transmission risk; neutered positive dogs receiving concurrent antibiotic therapy achieve better and more sustained bacteriological remission than intact dogs receiving antibiotics alone.
Euthanasia Considerations
Some veterinary infectious disease specialists and public health authorities recommend euthanasia as the most responsible option for confirmed-positive dogs in active breeding programs, particularly in large kennels where the infection has spread to multiple dogs and where the zoonotic risk to human handlers is a significant concern; the basis for this recommendation is the inability to reliably achieve microbiological cure and the ongoing shedding risk even in dogs that appear clinically normal after treatment; for individual pet dogs with brucellosis that are not in a breeding program, euthanasia is not required, and management with neutering plus combination antibiotics followed by serial monitoring (repeat serology every 3 to 6 months) is appropriate; the decision must balance the infection risk to in-contact dogs and humans against the owner’s bond with the dog and the dog’s quality of life.
Prevention in Breeding Programs
| Prevention Measure | Details |
|---|---|
| Pre-breeding testing of every dog before each mating | Both the male and female should be tested with RSAT (confirmed with CPA-AGID if positive) within 30 days before each breeding; one-time annual testing is insufficient because dogs can acquire infection between annual tests |
| Quarantine and testing of new dogs entering the kennel | Isolate new dogs for 30 days and test twice (at entry and at 30 days) before allowing contact with resident dogs; a single negative test at entry does not rule out incubating infection acquired just before purchase |
| Do not breed untested dogs | Dogs of unknown Brucella status (rescue dogs, stray dogs, dogs without recent negative test documentation) should not be mated until tested and confirmed negative |
| Biosafety during whelping and abortion | Wear gloves, eye protection, and a mask when handling reproductive secretions, aborted material, or placentas from any bitch; discard aborted material in sealed biohazard bags; disinfect whelping area with dilute bleach (1:10) or quaternary ammonium compounds; Brucella is susceptible to standard disinfectants when applied to clean surfaces but is protected by organic matter |
| Avoid shared housing of intact dogs from different sources | Dogs at dog shows, sporting events, and boarding facilities share environments; intact dogs housed together at unfamiliar facilities face unknown Brucella exposure; this is particularly relevant for sporting dog breeds that travel to field trials and compete alongside dogs from other kennels |
| No vaccine available | There is no licensed Brucella canis vaccine for dogs in the United States; prevention is entirely dependent on testing and management protocols |
Zoonotic Risk to Humans
Brucella canis is a zoonotic pathogen, meaning it can be transmitted from infected dogs to humans; however, the risk of human B. canis infection from dog contact is lower than the risk from B. abortus, B. melitensis, or B. suis contact with livestock or livestock products, and the disease in most immunocompetent humans is self-limiting; documented human risk groups include: breeders and kennel workers who handle aborted material, vaginal discharge, or semen from infected dogs without adequate protective equipment; veterinarians and veterinary technicians who perform reproductive examinations, artificial insemination, or whelping assistance on Brucella-positive dogs; laboratory personnel who process blood cultures or reproductive specimens from infected dogs (laboratory-acquired brucellosis is a documented occupational hazard); human B. canis infection produces a febrile illness with headache, myalgia, and malaise that typically resolves over several weeks without specific treatment; rare but serious complications in humans include endocarditis (infection of heart valves), discospondylitis, uveitis, and neurobrucellosis; immunocompromised individuals (HIV infection, organ transplant recipients, patients on immunosuppressive medications) face higher risk of serious human B. canis disease; Brucella canis infection is reportable to public health authorities in many US states.
US Cost Overview for Brucellosis
| Service | Typical US Cost |
|---|---|
| Veterinary examination | $60 to $150 |
| RSAT in-clinic screening test | $30 to $60 |
| CPA-AGID confirmatory serology (reference lab) | $60 to $120 |
| Blood culture for B. canis (reference lab, 7 to 21 days) | $80 to $180 |
| PCR for B. canis (blood or tissue) | $60 to $140 |
| Complete blood count and chemistry panel | $150 to $300 |
| Spinal radiographs (screening for discospondylitis) | $150 to $350 |
| Spinal MRI or CT (discospondylitis workup) | $1,200 to $3,000 |
| Doxycycline (8-week course, 30 kg dog) | $30 to $80 |
| Enrofloxacin (8-week course, 30 kg dog) | $40 to $100 |
| Castration (male) | $200 to $600 |
| Spay (female) | $300 to $800 |
| Semen evaluation (male, initial assessment) | $80 to $200 |
| Serial serology monitoring (every 3 to 6 months) | $60 to $120 per panel |
Age-Specific Considerations
Puppies (Under 12 Months)
- Puppies born to Brucella-positive bitches or exposed to infected milk from a Brucella-positive lactating dam can acquire infection in the neonatal period; clinical signs in neonatal puppies include failure to thrive, generalized lymphadenopathy, and bacteremia; puppies born from a Brucella-positive bitch’s infected litter should be tested by PCR or blood culture at 4 to 8 weeks of age; neonatal infection from an infected dam is a documented but underrecognized route of transmission; any kennel experiencing unexplained neonatal mortality or fading puppy syndrome should include maternal Brucella testing in the evaluation
- Doxycycline is generally avoided in puppies under 8 weeks of age because of the risk of tetracycline-class drug deposition in developing tooth enamel (causing permanent yellow-brown tooth discoloration) and potential effects on developing bone; enrofloxacin is also used with caution in puppies under 12 months due to concerns about cartilage effects at high doses; a fluoroquinolone plus trimethoprim-sulfamethoxazole combination has been used in young puppies when tetracyclines are contraindicated; specific dosing and protocol selection in puppies with brucellosis should be discussed with a veterinary infectious disease specialist
- Intact puppies older than 6 months entering a breeding program should be tested for B. canis before their first breeding; because the RSAT may be negative in the early weeks after infection (before antibodies reach detectable levels), recently acquired infection can be missed on initial screening; a 30-day quarantine with testing at entry and 30 days post-entry is more reliable than a single test at entry for newly purchased breeding dogs
Adult Dogs (1 to 8 Years)
- Adult intact dogs in active breeding programs represent the highest-risk group for brucellosis acquisition and transmission; the peak period for brucellosis diagnosis in case series coincides with the peak reproductive years (1 to 6 years in most breeds); the most important preventive measure for adult breeding dogs is the pre-breeding test policy: both the male and female should have a negative RSAT (confirmed negative) within 30 days before each mating, regardless of their testing history; a dog that tested negative 3 months ago at an annual health check can have acquired infection since that test, especially if it has been at dog shows, field trials, or boarding facilities where contact with unknown intact dogs occurred
- Adult dogs with brucellosis-associated discospondylitis require concurrent antibiotics (doxycycline plus enrofloxacin for a minimum of 8 to 12 weeks) and anti-inflammatory pain management (NSAIDs for mild cases; gabapentin or other neuropathic pain agents for nerve pain from spinal cord compression); serial spinal imaging (radiographs every 4 to 8 weeks) monitors the vertebral response to therapy; surgical intervention for spinal cord decompression is required in some cases with vertebral instability or progressive neurological signs despite medical management; any intact adult dog with discospondylitis should be tested for B. canis and for Staphylococcus pseudintermedius bacteremia (the most common bacterial cause of discospondylitis in intact dogs) as the two most likely bacterial causes
- Uveitis associated with brucellosis is treated with topical anti-inflammatory therapy (prednisolone acetate eye drops) and systemic antibiotics; brucellosis serology should be performed on any intact dog with uveitis of unknown origin, particularly if reproductive history or clinical signs suggest prior exposure; ocular brucellosis can cause intraocular pressure changes, corneal edema, and if untreated, vision loss
Senior Dogs (9 Years and Older)
- Senior dogs are rarely involved in active breeding programs, so the primary clinical significance of brucellosis in seniors relates to previously acquired infection that was never diagnosed; a senior dog with discospondylitis, chronic uveitis, or unexplained generalized lymphadenopathy may have had Brucella infection earlier in life; serology should be included in the workup of any senior dog with these findings, particularly if the dog was intact for some or all of its life; chronic Brucella infection can persist in macrophages and lymph nodes for years after initial infection, even in neutered dogs
- Antibiotic therapy for brucellosis in senior dogs must account for age-related organ function changes: doxycycline is primarily hepatically metabolized and is generally safe in senior dogs with normal liver function; enrofloxacin is renally cleared and dose adjustment is appropriate in senior dogs with reduced GFR (creatinine above 2.0 mg/dL); rifampin carries more hepatotoxic risk in older dogs and monthly ALT monitoring is warranted; the benefit of prolonged combination antibiotic therapy in a senior non-breeding dog with chronic Brucella infection must be weighed against the risk of adverse drug effects over an 8 to 12-week course in a dog with potentially reduced organ reserve
- Senior dogs with brucellosis-associated discospondylitis face the same treatment challenges as in other age groups but with the added complexity of age-related spinal degenerative changes (spondylosis deformans, facet joint arthritis) that can confuse the radiographic interpretation; MRI is superior to radiographs for distinguishing active discospondylitis from chronic degenerative spinal changes, and its use in senior dogs with spinal pain and a positive Brucella serology is strongly recommended before committing to a prolonged antibiotic course
Myths and Facts About Canine Brucellosis
My dog tested positive on the RSAT screening test, so he definitely has brucellosis and needs to be euthanized immediately.
A positive RSAT alone is not a confirmed diagnosis. The RSAT has a false-positive rate of 30 to 50 percent due to cross-reactivity with antibodies against other gram-negative bacteria. Every positive RSAT must be confirmed with CPA-AGID serology or blood culture before a definitive diagnosis is made. Euthanizing a dog based on an unconfirmed RSAT positive can result in the unnecessary death of a Brucella-negative dog. Always confirm with a more specific test before making management decisions.
We treated our dog with doxycycline for 8 weeks and she tested negative after treatment, so she is cured and safe to breed again.
Antibiotic treatment for brucellosis reduces bacteremia and can produce negative serology temporarily, but microbiological cure (complete elimination of B. canis from all tissues) is rarely achieved and cannot be confirmed by serology alone. Brucella persists in macrophages and lymph nodes even when blood cultures and serology are transiently negative. Relapse after apparently successful treatment is common. A confirmed-positive dog should not re-enter a breeding program regardless of post-treatment serology results because of the ongoing risk of reactivation and transmission.
Brucellosis only affects breeding dogs; my neutered pet is safe and does not need to be tested.
While the primary clinical impact of brucellosis is on reproductive performance in intact dogs, neutered dogs can acquire B. canis through non-sexual routes (contact with urine, aborted material, or reproductive secretions from infected dogs at kennels, dog parks, or dog shows). Neutered dogs with brucellosis can develop systemic complications including discospondylitis and uveitis. Any neutered dog with unexplained spinal pain, uveitis, or lymphadenopathy who has had contact with intact dogs or kennels should have brucellosis included in the differential diagnosis.
Red Flags: Signs Requiring Prompt Veterinary Evaluation
- Late-term abortion (days 45 to 55 of gestation) of morphologically normal but stillborn fetuses with a grey-green vaginal discharge in an intact bitch: this presentation is essentially pathognomonic for Brucella canis abortion; immediate RSAT testing of the bitch and any male she was mated with is required; the abortion discharge contains extremely high concentrations of B. canis and represents a significant exposure risk for any other dogs in the environment and for human handlers; the aborted material must be handled with gloves, mask, and eye protection and disposed of appropriately; the bitch should be isolated from other intact dogs pending serology results
- Painful scrotal swelling with scrotal skin changes (erythema, dermatitis) in an intact male from a breeding program: unilateral or bilateral epididymitis in a breeding dog should be considered brucellosis until proven otherwise; immediate RSAT testing is appropriate; other causes of acute scrotal swelling (testicular torsion, penetrating trauma, inguinal hernia) require urgent evaluation and can be distinguished by history, palpation, and ultrasound; do not delay RSAT testing while pursuing other differential diagnoses in a breeding male with scrotal swelling
- Progressive spinal pain and rear limb weakness in an intact dog that has been in a breeding program or has had contact with other intact dogs: Brucella discospondylitis must be considered alongside bacterial discospondylitis (Staphylococcus pseudintermedius) and other causes of spinal cord disease; RSAT serology and spinal imaging (radiographs first, then CT or MRI if radiographs are inconclusive) are both required; delaying the Brucella test while treating presumptively for bacterial discospondylitis allows ongoing Brucella shedding and transmission to in-contact dogs and humans
- A kennel or breeding program with multiple dogs experiencing unexplained reproductive failure (failed conceptions, small litters, neonatal losses) over consecutive breeding seasons: a pattern of reproductive failure across multiple dogs in a program strongly suggests B. canis has entered the kennel; testing all intact dogs in the program with RSAT (confirmed with CPA-AGID for any positive) is urgent, and the kennel should be quarantined from outside dogs until all tests are complete and results are known
Frequently Asked Questions About Brucellosis in Dogs
What is brucellosis in dogs?
Canine brucellosis is a bacterial infection caused by Brucella canis, a gram-negative intracellular organism that survives inside macrophages. It primarily affects intact dogs in breeding programs, causing late-term abortion in females, epididymitis and infertility in males, and systemic complications including discospondylitis and uveitis in both sexes. It is transmitted mainly through mating and contact with reproductive secretions. Brucella canis is a zoonotic pathogen that can cause illness in humans.
What are the symptoms of brucellosis in dogs?
In intact females: late-term abortion of morphologically normal stillborn fetuses (days 45 to 55), grey-green vaginal discharge, repeated failure to conceive, and generalized lymphadenopathy. In intact males: scrotal swelling and pain from epididymitis, orchitis, testicular atrophy in chronic infection, and infertility. Both sexes may develop discospondylitis (spinal pain, rear limb weakness), uveitis, and lymphadenopathy. Many infected dogs appear clinically normal while shedding the organism in reproductive secretions.
How is brucellosis diagnosed in dogs?
The rapid slide agglutination test (RSAT) is the standard in-clinic screening test with high sensitivity but a 30 to 50 percent false-positive rate. Every positive RSAT must be confirmed with a more specific test: CPA-AGID serology or blood culture. Blood culture grows B. canis after 7 to 21 days and is the definitive gold standard. PCR on blood or reproductive secretions is fast and highly accurate. The diagnostic algorithm is RSAT screen, then CPA-AGID confirmation, then culture or PCR for definitive confirmation.
Can brucellosis in dogs be cured?
No antibiotic protocol reliably achieves microbiological cure of canine brucellosis because B. canis lives inside macrophages where antibiotics cannot fully penetrate. Combination therapy with doxycycline plus enrofloxacin or rifampin for 8 weeks reduces bacteremia and clinical signs and combined with neutering provides the best long-term disease control. Relapse after treatment is common. Confirmed-positive dogs should not be used for breeding regardless of post-treatment serology results because reactivation and resumed shedding are possible.
Can humans get brucellosis from dogs?
Yes. Brucella canis is a confirmed zoonotic pathogen. Human infection most commonly occurs through direct contact with infected reproductive secretions (aborted material, vaginal discharge, semen) without adequate protective equipment, or through laboratory exposure during culture processing. Most human B. canis infections cause a self-limiting febrile illness, but serious complications including endocarditis and discospondylitis have been reported. Gloves, mask, and eye protection should be worn when handling reproductive secretions from any dog of unknown Brucella status.
How do I prevent brucellosis in my breeding program?
Test both the male and female with RSAT (confirmed with CPA-AGID if positive) within 30 days before every mating. Quarantine and test all new dogs entering the kennel for 30 days before contact with resident dogs. Never breed a dog of unknown Brucella status. Wear protective equipment when handling whelping or abortion materials. There is no licensed vaccine for B. canis in the United States, so prevention depends entirely on testing and management protocols.
Does my neutered pet dog need to be tested for brucellosis?
Routine Brucella testing is not recommended for all neutered pet dogs with no exposure to breeding dogs or kennels. However, a neutered dog that has had contact with intact dogs in a kennel environment, dog shows, or multi-dog households where intact dogs are present should be tested if unexplained spinal pain, uveitis, or generalized lymphadenopathy develops. Neutered dogs can still acquire and harbor B. canis through non-sexual exposure routes, and the organism can cause systemic complications in the absence of reproductive signs.
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