Sandra Carson 
Brucellosis in Dogs
Brucellosis in Dogs: Symptoms, Diagnosis, and Treatment
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That unexplained infertility, the late-term abortion, the swollen testicles - these concerning reproductive issues could indicate your dog is suffering from brucellosis, a serious bacterial infection that affects the reproductive system and can be transmitted to humans.
Brucellosis is a contagious bacterial infection caused by Brucella canis that primarily affects the reproductive system in dogs. This disease can cause infertility, abortions, and chronic health issues, and poses a zoonotic risk to humans.
In this comprehensive guide, we'll explore everything you need to know about brucellosis in dogs - from recognizing the subtle reproductive symptoms to understanding the complex diagnostic process and confronting the difficult treatment decisions.
Keep reading to discover how to protect your dog from this dangerous infection and what to do if you suspect your canine companion may be affected. Your attention to this guide could prevent serious health consequences for your dog and your family.
What is Brucellosis?
Brucellosis is a contagious bacterial infection caused by Brucella canis, a small, intracellular, gram-negative bacterium that primarily affects the reproductive system in dogs. This disease is considered a venereal disease that can cause significant reproductive problems and has important public health implications due to its zoonotic potential.
Did You Know?
Brucella canis was first identified in the United States in 1966 and is now found worldwide. While dogs are the preferred host for B. canis, they can occasionally become infected with other Brucella species through exposure to infected domestic production animals. The bacteria can survive in the environment for months under moist, cool, and dark conditions, but is easily eliminated with proper disinfectants like bleach.
Once a dog is infected, the organism is taken up by the reticuloendothelial system, where it remains intracellular and travels to the lymph nodes, spleen, and liver. Bacteremia typically begins 1-4 weeks after exposure and can persist intermittently for years.
Key characteristics of brucellosis include:
- Reproductive Focus: Primarily targets reproductive organs including testicles, prostate, epididymis, uterus, and placenta
- Chronic Infection: Considered a permanent infection that cannot be completely eliminated
- Zoonotic Potential: Can be transmitted from dogs to humans, though risk is generally low
- Worldwide Distribution: Found globally with increasing cases in previously low-prevalence areas
The bacteria localizes in reproductive organs and can cause significant damage to these tissues. Infected dogs may appear healthy for extended periods, as the disease can remain subclinical for years, especially in spayed or neutered individuals or those not involved in breeding activities.
Symptoms and Clinical Signs of Brucellosis
Brucellosis symptoms in dogs are primarily associated with the reproductive tract, but can also affect other body systems. The clinical presentation can vary significantly, with some dogs showing no obvious symptoms while others develop severe reproductive or systemic issues.
Reproductive Symptoms in Females
- Abortion (typically late term, 45-59 days)
- Stillbirths
- Weak puppies that die soon after birth
- Infertility or difficulty conceiving
- Vaginal discharge
- Placentitis and metritis
Reproductive Symptoms in Males
- Epididymitis (swollen testicles)
- Orchitis (testicular inflammation)
- Prostatitis
- Skin rash on scrotum
- Testicular atrophy with chronic infection
- Infertility
Systemic Symptoms
- Lethargy and weakness
- Swollen lymph nodes
- Back pain or discospondylitis
- Joint inflammation or arthritis
- Eye inflammation (uveitis)
- Poor coat condition
Important Note
Fever is not a hallmark clinical finding in dogs with brucellosis as it is in other species. Many infected dogs show no obvious signs of illness, especially in early stages or when not involved in breeding activities. The absence of fever or other systemic signs does not rule out brucellosis infection. Dogs can carry and shed the bacteria for years without showing clinical symptoms, making testing essential for detection.
In chronic cases, brucellosis can cause discospondylitis (inflammation of spinal discs), uveitis (eye inflammation), arthritis in multiple joints, and glomerulonephritis (kidney inflammation). These conditions result from long-term immune stimulation and antigen-antibody deposition in various tissues.
How Brucellosis Spreads
Brucellosis is highly contagious among dogs and can be transmitted through several routes. Understanding the transmission methods is crucial for prevention and control, especially in multi-dog households or breeding facilities.
Primary Transmission Routes
1 Venereal Transmission
Direct transmission during mating is a common route of infection. Infected dogs shed large numbers of bacteria in semen and vaginal secretions.
2 Contact with Infected Fluids
Dogs can contract the infection by licking or sniffing contaminated vaginal discharges, aborted fetuses, placental tissues, or urine.
3 Oral Transmission
Ingestion of contaminated materials is a significant route of transmission, particularly in kennel settings where dogs may contact infected fluids.
4 Mucous Membrane Exposure
The bacteria can enter through conjunctival (eye) or oronasal membranes when dogs are exposed to contaminated secretions.
| Transmission Route | Description | Significance |
|---|---|---|
| Venereal Contact | During mating through infected semen or vaginal secretions | Primary route in breeding situations; highly efficient transmission |
| Contact with Birth Materials | Exposure to aborted fetuses, placentas, or vaginal discharge | Extremely high risk; females shed bacteria for 4-6 weeks after abortion |
| Oral Ingestion | Licking contaminated urine, secretions, or birth materials | Common in kennel settings; dogs naturally investigate with mouth |
| Mucous Membrane | Through eyes, nose, or mouth via contaminated fluids | Possible route; includes sniffing contaminated urine or secretions |
| Transplacental/Whelping | From infected mother to puppies during birth or through milk | Puppies can be born infected or acquire infection during nursing |
| Environmental | Contact with contaminated surfaces, bedding, or equipment | Bacteria can survive for months in ideal conditions; fomite transmission possible |
Important Note
After a female dog aborts due to brucellosis, she continues to secrete fluids packed with Brucella bacteria for four to six weeks, creating an extended period of high contagion. During this time, strict isolation and hygiene measures are critical to prevent spread to other dogs. The bacteria can survive in the environment for months under moist, cool, and dark conditions, but are easily eliminated with proper disinfectants like bleach.
Both intact and neutered dogs can shed the bacteria, with intact animals typically shedding higher concentrations in reproductive fluids. Urine and saliva contain lower concentrations of bacteria compared to genital secretions, but still pose a transmission risk, particularly in situations of prolonged close contact.
Diagnosis and Testing for Brucellosis
Diagnosing brucellosis can be challenging due to the intermittent nature of bacteremia and limitations of available tests. A combination of clinical signs, history, and multiple diagnostic tests is often necessary for accurate diagnosis.
Diagnostic Challenges
- Intermittent Bacteremia: Bacteria may not always be present in blood samples
- Intracellular Nature: Bacteria hide inside cells, evading detection
- Variable Antibody Response: Antibody levels can fluctuate over time
- Subclinical Infections: Many infected dogs show no symptoms
- Cross-Reactions: Some tests may produce false positives
Diagnostic Tests for Brucellosis
| Test Type | Methodology | Purpose and Accuracy |
|---|---|---|
| Rapid Slide Agglutination Test (RSAT) | Detects antibodies in blood; rapid results | Screening test; negative results reliable, but up to 60% false positives occur |
| Tube Agglutination Test (TAT) | Measures antibody titers quantitatively | Screening and monitoring; provides numerical titer results |
| Agar Gel Immunodiffusion (AGID) | Detects specific antibodies; more specialized | Confirmatory test; highly specific, best used 12 weeks to 1 year post-infection |
| Immunofluorescent Antibody (IFA) | Uses fluorescent tags to detect antibodies | Screening test; must be sent to reference laboratory |
| ELISA Tests | Enzyme-linked immunosorbent assay | Detects antibodies; various formats available |
| PCR Testing | Polymerase chain reaction detects bacterial DNA | Highly sensitive and specific; can detect low levels of infection |
| Bacterial Culture | Growing bacteria from samples | Gold standard but challenging; biosafety concerns |
Proper interpretation of brucellosis test results requires understanding their limitations and appropriate uses:
- RSAT: Best used as a screening test. Negative results are reliable, but positive results require confirmation with more specific tests due to high false-positive rates
- AGID: Considered the most specific test for confirmation. The version that detects cytoplasmic proteins is particularly accurate
- Testing Timeline: It can take 2-4 weeks for seroconversion after infection, and up to 12 weeks in some cases. Testing too early may produce false negatives
- Antibiotic Effects: Antibiotic treatment with tetracyclines can lower antibody levels enough to produce negative TAT results, but this doesn't indicate cure
- Diagnostic Approach: Most veterinarians use an initial screening test (RSAT or IFA) followed by confirmatory testing (AGID) for positive results
No single test is 100% accurate for brucellosis diagnosis. The combination of clinical history, physical findings, and multiple test modalities provides the most reliable diagnosis.
For breeding dogs, regular testing every 3-6 months is recommended, with additional testing before introducing new dogs to a kennel. Dogs with positive tests should be removed from breeding programs regardless of whether they show clinical symptoms.
Treatment Options for Brucellosis
Brucellosis presents significant treatment challenges, with no known therapy that completely eliminates B. canis infection. The intracellular nature of the bacteria and its ability to persist in tissues make complete eradication extremely difficult.
⚠️ Important Treatment Consideration
Due to the zoonotic potential and difficulty of complete cure, many veterinary and public health authorities recommend euthanasia for infected dogs, particularly in breeding settings or households with immunocompromised individuals. When euthanasia is declined, strict lifelong management protocols must be implemented to reduce human exposure risk. Brucellosis is considered a permanent infection, and precautions must be maintained for the life of the animal.
Antibiotic Therapy Protocols
While no antibiotic protocol guarantees complete cure, several combinations have been used with varying success:
- Tetracycline and Streptomycin: Tetracycline given twice daily for one month combined with daily streptomycin injections during the first and last week. This was historically the most effective regimen, with over half of dogs considered cured in one study, but streptomycin is now difficult to obtain.
- Minocycline and Streptomycin: Minocycline (a tetracycline derivative) given once daily for four weeks with streptomycin injections during the first and last weeks.
- Doxycycline and Aminoglycosides: Doxycycline combined with an aminoglycoside like gentamycin, with daily injections of the aminoglycoside for the first and last week of a four-week doxycycline course. Newer literature suggests replacing the aminoglycoside with rifampin.
- Quinolone Antibiotics: Enrofloxacin and other quinolones have been proposed as less toxic alternatives to aminoglycosides and may emerge as the best replacement for streptomycin.
Antibiotic treatment typically continues for a minimum of 2-3 months, with ongoing monitoring. Even with extended treatment, many dogs remain infected and may experience recrudescence after antibiotics are discontinued.
Adjunctive Measures and Management
When treating brucellosis, several adjunctive measures are essential:
- Surgical Sterilization: Spaying or neutering infected dogs is strongly recommended to reduce shedding of bacteria in reproductive fluids and decrease transmission risk.
- Lifelong Monitoring: Regular testing (monthly initially) is necessary to monitor infection status, as antibiotics can suppress but not eliminate the infection.
- Strict Isolation: Infected dogs should be confined to the owner's property and prevented from contacting other dogs. Veterinary and grooming services should be provided by mobile services with appropriate protective measures.
- Environmental Decontamination: Thorough cleaning and disinfection with bleach solutions is essential, particularly areas contaminated with urine, reproductive fluids, or birth materials.
- No Breeding: Infected dogs must be permanently removed from breeding programs regardless of treatment.
Treatment Considerations
Complex and long-term:
Lifelong Management
Treatment involves extended antibiotic courses, regular monitoring tests, and potential isolation requirements. The emotional and time commitment is significant, and complete cure is unlikely.
Prognosis and Outcome
Guarded to Poor
Permanent Infection
Infection is generally considered permanent even with treatment. The goal shifts to managing symptoms and reducing transmission risk rather than achieving complete cure.
Despite aggressive treatment, Brucella canis infection is generally considered permanent. The focus shifts from cure to management: controlling symptoms, minimizing bacterial shedding, and preventing transmission to other dogs and humans. Dogs should be monitored for late complications like discospondylitis, uveitis, or arthritis, which may require additional supportive treatment.
Prevention Strategies
Preventing brucellosis is significantly more effective than treating it, given the challenges associated with eradication of the infection. A comprehensive prevention strategy is essential, particularly for breeding kennels or multi-dog households.
Kennel Management and Breeding Protocols
| Prevention Method | Implementation | Effectiveness |
|---|---|---|
| Regular Testing | Test all breeding dogs every 3-6 months; test new dogs before introduction | Highly effective for early detection; essential for breeding programs |
| Quarantine Procedures | Isolate new dogs for 1-2 months; perform two tests 3-4 weeks apart | Critical for preventing introduction; allows time for seroconversion |
| Import Screening | Test imported dogs before entry; be aware of high-prevalence regions | Essential given rising cases from imported dogs |
| Biosecurity Measures | Restrict access to kennels; control movement between facilities | Reduces risk of introduction from external sources |
Additional Prevention Measures
- Pre-Breeding Testing: Always test both male and female dogs before breeding, and insist on seeing test results from mating partners
- Hygiene Protocols: Practice strict hygiene when handling whelping dogs or birth materials; wear gloves and protective equipment
- Environmental Management: Promptly remove and properly dispose of aborted fetuses, placentas, and contaminated bedding
- Disinfection: Use appropriate disinfectants like bleach solutions on contaminated surfaces
- Education: Ensure all staff, breeders, and handlers understand brucellosis risks and prevention measures
- Reporting: Follow local reporting requirements; brucellosis is a reportable disease in many areas
Prevention Cost-Benefit
Regular testing and preventive measures are far more economical than dealing with an outbreak in a kennel. The cost of testing is minimal compared to the economic losses from infertility, abortions, and the potential need to depopulate affected kennels. More importantly, prevention protects both canine and human health from this serious disease. Many breeding organizations now require brucellosis testing as part of their certification programs.
In the event of a positive case in a kennel, immediate quarantine of the facility is essential. All dogs should be tested, with positive dogs removed from the kennel. The kennel should remain quarantined until all dogs have tested negative three times at 3-month intervals. This rigorous approach is necessary to eliminate the infection from a breeding population.
Zoonotic Risk: Brucellosis in Humans
Brucella canis is a zoonotic pathogen, meaning it can be transmitted from dogs to humans. While human infection is generally uncommon and typically less severe than infections with other Brucella species, it remains an important public health consideration.
Transmission Risk to Humans
- Higher Risk Groups: Veterinarians, veterinary staff, dog breeders, kennel workers, and laboratory personnel handling samples have increased exposure risk
- Transmission Routes: Humans typically acquire infection through contact with infected birth materials, vaginal discharges, semen, urine, or aborted fetuses
- Entry Points: Bacteria can enter through mucous membranes (eyes, nose, mouth), broken skin, or via inhalation of contaminated aerosols
- Lower Risk: Pet owners with casual contact have relatively low risk, especially with intact skin and no exposure to reproductive fluids
Human Symptoms and Diagnosis
In humans, B. canis infection typically causes flu-like symptoms that may develop over days, weeks, or even months after exposure:
- Fever (often undulant - coming and going)
- Headache
- Joint and muscle pain
- Fatigue and weakness
- Swollen lymph nodes
- Night sweats
- Weight loss
In rare cases, more serious complications can occur, including endocarditis (heart infection), arthritis, neurological issues, or reproductive problems. The infection can become chronic if not properly treated. Diagnosis in humans requires specific testing, as routine cultures may not detect B. canis.
Protective Measures for Humans
- Personal Protective Equipment (PPE): Wear gloves, eye protection, and masks when handling whelping dogs, birth materials, or cleaning contaminated areas
- Hand Hygiene: Wash hands thoroughly with soap and water after handling dogs, especially after contact with bodily fluids
- High-Risk Individuals: Pregnant women, immunocompromised individuals, young children, and the elderly should avoid contact with infected dogs
- Environmental Controls: Properly disinfect contaminated surfaces with bleach solutions
- Education: Ensure all family members understand risks and protective measures
Public Health Reporting
Brucellosis is a reportable disease in many states and countries. Veterinarians are required to report positive cases to public health authorities. While B. canis infection is not currently nationally reportable in all areas, many states have reporting requirements. Other Brucella species are reportable in all U.S. states. Reporting helps track disease patterns and implement appropriate public health measures.
Despite the zoonotic potential, the overall risk to most pet owners is low, especially with appropriate precautions. However, the serious nature of the disease in both dogs and humans warrants careful attention to prevention and control measures. Individuals with exposure to infected dogs who develop flu-like symptoms should consult their healthcare provider and mention the possible brucellosis exposure.
Frequently Asked Questions
No, brucellosis cannot be reliably cured in dogs. While antibiotics can help control the infection and reduce bacterial shedding, no treatment is completely effective at eliminating B. canis infection. The bacteria can persist in tissues despite treatment, and recrudescence (return of infection) is common after antibiotics are discontinued. For this reason, infection is generally considered permanent, and management focuses on controlling symptoms and reducing transmission risk rather than achieving complete cure.
This is a difficult decision that depends on several factors. Many veterinary and public health authorities recommend euthanasia, particularly for dogs in breeding facilities or households with high-risk individuals (pregnant women, immunocompromised persons, young children). However, if euthanasia is declined, infected dogs can be managed as pets with strict precautions: surgical sterilization, lifelong antibiotics in some cases, strict confinement to prevent contact with other dogs, and meticulous hygiene to reduce human exposure. The dog should never be bred or sold. This decision should be made in consultation with your veterinarian and consideration of the potential risks to human and other animal health.
Brucellosis prevalence varies geographically. The disease is found worldwide, with higher prevalence in certain regions including parts of the southern United States, South America, Eastern Europe, the Middle East, and Asia. In areas previously considered low-prevalence, cases are increasing due to importation of infected dogs. In breeding kennels with introduced infection, prevalence can be high due to the contagious nature of the disease. Overall prevalence in the general pet population is low, but higher in breeding dogs and dogs from shelters or rescue organizations with international sources.
No, there is currently no commercially available vaccine for brucellosis in dogs. Prevention relies entirely on testing protocols, quarantine measures for new animals, and strict hygiene practices. Research continues, but vaccine development has been challenging due to the complex nature of the immune response to Brucella bacteria and safety concerns. For now, biosecurity measures and regular testing remain the primary prevention strategies.
For optimal safety, new dogs should be quarantined for at least one month, and preferably two months. Two brucellosis tests should be performed during this period: one at the beginning of quarantine and another 3-4 weeks later. Since it can take 8-12 weeks from infection for tests to become positive, this approach helps detect infections that might not be apparent initially. This is particularly important for dogs from unknown backgrounds, shelters, or imported dogs from regions with higher brucellosis prevalence.
Yes, while breeding is a common transmission route, dogs can contract brucellosis through other means. These include:
- Contact with infected birth materials or aborted fetuses
- Licking contaminated urine or genital secretions
- Sniffing contaminated surfaces or materials
- Contact with contaminated bedding, equipment, or environments
- In rare cases, through aerosol transmission in confined spaces
- Transplacental transmission or through milk from infected mother to puppies
This is why even pets that are not used for breeding can potentially contract brucellosis if exposed to infected dogs or contaminated environments.
Bottom Line: Protecting Your Dog from Brucellosis
Brucellosis is a serious, contagious bacterial infection that primarily affects the reproductive system in dogs and poses zoonotic risks to humans. The key to protection lies in comprehensive prevention including regular testing for breeding dogs, strict quarantine protocols for new animals, and meticulous hygiene when handling whelping dogs or reproductive materials. If your dog shows reproductive issues like late-term abortions, stillbirths, swollen testicles, or infertility - especially with a history of contact with other dogs - consult your veterinarian for appropriate testing. Treatment is challenging and rarely results in complete cure, making prevention through responsible breeding practices and biosecurity measures paramount. Remember that infected dogs require lifelong management with strict precautions to protect both human and animal health, and euthanasia is often recommended due to the permanent nature of the infection and public health concerns.
References and Further Readings
1- Canine brucellosis: a review of diagnostic methods and treatment
2- Canine brucellosis: an update
3- Brucella canis: A Review of the Literature and Clinical Presentation in Dogs
4- Diagnosis and management of Brucella canis in dogs
5- Canine brucellosis: insights into the epidemiologic situation in Europe
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