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Basics ⬇

Basics

Definition

  • Contagious disease of dogs caused by Brucella canis, a small, intracellular, Gram-negative organism.
  • Characterized by abortion and infertility in females and epididymitis and testicular atrophy in males.

Pathophysiology

B. canis-an intracellular parasite; has a propensity for growth in lymphatic, placental, and male genital (epididymis and prostate) tissues.

Systems Affected

  • Hemic/Lymph/Immune-lymph nodes and spleen; bone marrow; mononuclear leukocytes.
  • Reproductive-target tissues of gonadal steroids (gravid uterus, fetus, testes [epididymides], prostate gland).
  • Other tissues-intervertebral discs, anterior uvea, meninges (uncommon).

Genetics

  • No known genetic predisposition.
  • Occurs most commonly in beagles.

Incidence/Prevalence

  • Incidence unknown.
  • Seroprevalence rates-not accurately defined; false-positive results common with agglutination tests.
  • Prevalence-relatively low (1–18%) in the United States and Japan; in the United States, higher in rural areas of the south; in Mexico and Peru, 25–30% in stray dogs.

Geographic Distribution

Stray dogs, pets, and kennels-United States (mostly beagles), Mexico, Japan, and several South American countries; seen in Spain, Tunisia, China, and Bulgaria; individual outbreaks in Germany and the former Czechoslovakia (some traced to the importation of dogs).

Signalment

Species

Dogs and, infrequently, humans

Breed Predilections

  • No evidence of breed susceptibility, but exceptionally high prevalence in beagles.
  • Infected Labrador retrievers and several other breeds found in commercial kennels (“puppy mills”).

Mean Age and Range

  • No age preference.
  • Most common in sexually mature dogs.

Predominant Sex

  • Both sexes are affected.
  • More common in females.

Signs

General Comments

Suspect whenever female dogs experience abortions or reproductive failures or males have genital disease.

Historical Findings

  • Affected animals, especially females, may appear healthy or have vague signs of illness.
  • Lethargy.
  • Loss of libido.
  • Swollen lymph nodes.
  • Back pain.
  • Abortion-commonly at 6–8 weeks after conception, although pregnancy may terminate at any stage.

Physical Examination Findings

  • Males-swollen scrotal sacs, often with scrotal dermatitis; enlarged and firm epididymides.
  • Chronic infection-unilateral or bilateral testicular atrophy; spinal pain; posterior weakness; ataxia.
  • Chronic and recurrent unilateral anterior uveitis without other systemic signs of disease; also includes iris hyperpigmentation, vitreal infiltrates, and multifocal chorioretinitis.
  • Fever rare.
  • Enlarged superficial lymph nodes (e.g., retropharyngeal, external inguinal) common.
  • Vaginal discharge may last for several weeks after an abortion.

Causes

B. canis-Gram-negative coccobacillus; morphologically indistinguishable from other members of the genus; unlike other Brucella spp. (e.g., B. abortus, B. suis, and B. melitensis) can result in a high rate (50%) of false-positive reactions with commonly used tests.

Risk Factors

  • Breeding kennels and pack hounds.
  • Risk increases when popular breeding animals become infected.
  • Contact with strays in endemic areas.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Abortions-maternal, fetal, or placental abnormalities.
  • Systemic infections-canine distemper, canine herpesvirus infection, B. abortus infection, hemolytic streptococci, E. coli, leptospirosis, and toxoplasmosis.
  • Inguinal hernias-may be provoked by epididymitis and scrotal edema; also caused by blastomycosis and other granulomatous infections, and Rocky Mountain spotted fever.
  • Discospondylitis-fungal infections, actinomycosis, staphylococcal infections, nocardiosis, streptococci, or Corynebacterium diphtheroids.

CBC/Biochemistry/Urinalysis

  • Generally normal in uncomplicated cases.
  • Chronically infected dogs may show hyperglobulinemia (with concurrent hypoalbuminemia).
  • CSF-pleocytosis mainly consisting of neurtophils, and elevated protein in meningoencephalitis but normal in discospondylitis.
  • Urinalysis usually normal even if bacteria can be cultured from urine.

Other Laboratory Tests

Serologic testing-most commonly used diagnostic method; subject to error; false-positive reactions to lipopolysaccharide antigens of several species of bacteria common with the RSAT and mercaptoethanol tube agglutination tests.

RSAT

  • Commercially available; simple and rapid.
  • Detects infected dogs 3–4 weeks after infection; accurate in identifying non-infected (“negative”) dogs.
  • Suffers a high rate (50%) of false-positive reactions.
  • Results must be confirmed by other tests.

Mercaptoethanol Tube Agglutination Test

  • Semiquantitative.
  • Generally performed by commercial diagnostic laboratories.
  • Provides information similar to the RSAT.
  • Suffers from lack of specificity; good screening test.

AGID Tests

  • Cell wall antigen test-employs a lipopolysaccharide antigen derived from the cell walls of B. canis; highly sensitive; test conditions not standardized; frequent false positives; not recommended.
  • Soluble antigen test-employs soluble antigens that consist of proteins extracted from the bacterial cytoplasm; antigens highly specific for antibodies against Brucella spp. (including B. canis, B. abortus, and B. suis); reactive antibodies appear 4–12 weeks after infection and persist for a long time; may give precipitin lines after other tests become equivocal or negative; highly recommended.
  • ELISA-using purified cytoplasmic antigens but not yet commercially available.
  • PCR-shown to be more sensitive than blood culture and serology in detecting infection in human patients. Sensitive in identifying early infections but not yet commercially available.

Imaging

  • Radiographic evidence of discospondylitis-test for brucellosis.
  • Radiographic changes are slow to develop and may not be present even when spinal pain is present.

Diagnostic Procedures

Isolation of Organism

  • Blood cultures-when clinical and serologic findings suggest the diagnosis; Brucella are readily isolated from the blood of infected dogs if they have not received antibiotics; onset of bacteremia occurs 2–4 weeks after oral-nasal exposure and may persist for 8 months to 5.5 years.
  • Cultures of vaginal fluids-after an abortion; usually give positive results.
  • Cultures of semen or urine-not practical for routine diagnosis, because overgrowth of contaminants is common.
  • Contaminated samples-media that contain antibiotics (e.g., Thayer-Martin medium) have proven useful.

Semen Quality

  • Sperm motility, immature sperm, inflammatory cells (neutrophils)-with epididymitis.
  • Abnormalities-usually evident by 5–8 weeks post-infection; conspicuous by 20 weeks.
  • Aspermia without inflammatory cells-common with bilateral testicular atrophy.

Lymph Node Biopsy

  • Reveal lymphoid hyperplasia with large numbers of plasma cells.
  • If done in a sterile manner, tissues should be cultured on appropriate media.
  • Intracellular bacteria-may be observed in macrophages with special stains (e.g., Brown-Brenn stain).
  • Histopathologic examination of the testes-often reveals necrotizing vasculitis, infiltration of inflammatory cells, and granulomatous lesions.

Pathologic Findings

  • Gross findings-lymph node enlargement; splenomegaly; males: enlarged and firm epididymides, scrotal edema, or atrophy of one or both testes; chronic infection: anterior uveitis and discospondylitis.
  • Microscopic changes-relatively consistent; diffuse lymphoreticular hyperplasia; chronic infection: lymph node sinusoids with abundant plasma cells and macrophages that contain bacteria-diffuse lymphocytic infiltration and granulomatous lesions in all genitourinary organs (especially prostate, epididymis, uterus, and scrotum); may be extensive inflammatory cell infiltration and necrosis of the prostate parenchyma and seminiferous tubules.
  • Ocular changes-granulomatous iridocyclitis; exudative retinitis; leukocytic exudates in the anterior chamber.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

Outpatient

Activity

Restrict working dogs

Client Education

  • Client should be aware that the goal of treatment is the eradication of B. canis from the animal (seronegative status and no bacteremia for at least 3 months), but sometimes the result is persistent low antibody titers with no systemic infection.
  • Inform client that antibiotic treatment, especially minocycline and doxycycline, is expensive, time-consuming, and controversial (because outcomes are uncertain).
  • Treatment is not recommended for breeding or commercial kennels; it is recommended only for non-breeding dogs or those that have been spayed or castrated.
  • Before treatment is attempted for an intact household pet or breeding dog, the client must clearly agree that the animal must be neutered or destroyed if treatment fails.

Surgical Considerations

Neutering/spaying plus treatment-when euthanasia is unacceptable to an owner.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Several therapeutic regimens have been evaluated, but results have been equivocal.
  • Most successful-combination of a tetracycline (tetracycline hydrochloride, chlortetracycline, or minocycline at 25 mg/kg PO q8h for 4 weeks) or doxycycline (10 mg/kg PO q12h for 4 weeks) and dihydrostreptomycin (10 mg/kg IM q8h during weeks 1 and 4).
  • Enrofloxacin (5 mg/kg PO q24h for 4 weeks) alone shows poor efficacy.

Contraindications

  • Tetracyclines-do not use in immature pups.
  • Gentamicin-contraindicated with kidney disease.

Precautions

Gentamicin-monitor renal function closely.

Alternative Drug(s)

Gentamicin-3 mg/kg q12h; limited success; insufficient data on the efficacy combined with tetracycline.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Serologic tests-monthly for at least 3 months after completion of treatment; continuous, persistent decline in antibodies to negative status indicates successful treatment.
  • Recrudescent infections (rise in antibody levels and recurrence of bacteremia after therapy)-retreat, neuter and re-treat, or euthanize.
  • Blood cultures-negative for at least 3 months after completion of treatment.

Prevention/Avoidance

  • Vaccine-none; would complicate serologic testing.
  • Testing-all brood bitches, before they come into estrus if a breeding is planned; males used for breeding, at frequent intervals.
  • Quarantine and test all new dogs twice at monthly intervals before allowing them to enter a breeding kennel.

Possible Complications

  • Owners may be reluctant to neuter or destroy valuable dogs, regardless of treatment failure.
  • Remind owners of ethical considerations and their obligation not to sell or distribute infected dogs.

Expected Course and Prognosis

  • Prognosis guarded.
  • Infected for <3–4 months-likely to respond to treatment.
  • Chronic infections-males may fail to respond to therapy.
  • Discospondylitis cases-may need repeated drug treatment but surgical intervention is rarely needed.
  • Multiple drug combination therapy with gentamicin or streptomycin, doxycycline, enrofloxacin, and rifampin has been successful in treating ocular disease in dogs.
  • Successfully treated (seronegative) dogs-fully susceptible to reinfection.

Miscellaneous ⬆

Miscellaneous

Zoonotic Potential

  • Human infections-reported; usually mild; respond readily to tetracyclines.
  • However, an outbreak in six members of a family living in close contact with an infected bitch has been reported.

Pregnancy/Fertility/Breeding

  • Abortions at 45–60 days of gestation typical.
  • Pups from infected bitches may be infected or normal.

Synonyms

Contagious canine abortion

Abbreviations

  • AGID = agar gel immunodiffusion
  • CSF = cerebrospinal fluid
  • ELISA = enzyme-linked immunosorbent assay
  • PCR = polymerase chain reaction
  • RSAT = rapid 2-mercaptoethanol slide agglutination test

Author Stephen C. Barr

Consulting Editor Stephen C. Barr

Client Education Handout Available Online

Suggested Reading

Greene CE, Carmichael LE. Canine brucellosis. In: Greene CE, ed., Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, MO: Saunders Elsevier, 2012, pp. 398–411.

Kauffman LK, Bjork JK, Gallup JM, et al. Early detection of Brucella canis via quantitative polymerase chain reaction analysis. Zoonoses and Public Health 2014, 61(1):48–54.

Keid LB, Soares RM, Vasconcellos SA, et al. Comparison of agar gel immunodiffusion test, rapid slide agglutination test, microbiological culture, and PCR for the diagnosis of canine brucellosis. Res Vet Sci 2009, 86:22–26.

Ledbetter EC, Landry MP, Stokol T, et al. Brucella canis endophthalmitis in 3 dogs: Clinical features, diagnosis, and treatment. Vet Ophthalmology 2009, 12:183–191.

Lucero NE, Corazza R, Almuzara MN, et al. Human Brucella canis outbreak linked to infection in dogs. Epidemiol Infect 2009, 5:1–6.