Brucella canis (small gram-negative rod)

Most veterinarians are aware of the zoonotic risks of the other Brucella species (abortus, suis, melitensis). B. canis is often overlooked due to the mild clinical signs it causes. Dogs and wild canidae are susceptible while felines are resistant. The bacteria penetrates mucous membranes including oral, vaginal and conjunctiva. Infected female dogs transmit the bacteria during estrus, at breeding, and after abortion with shedding of B. canis occurring up to 6 weeks post abortion. Transmission can occur in utero, via fomites, vaginoscopy, blood transfusion, contaminated surgeries, or artificial insemination.

Dogs

Adults are rarely seriously ill. Most common clinical signs include diffuse lymphadenopathy, splenomegaly, and occasionally fever. In sexually mature dogs, many clinical signs are referrable reproductive disorders. In females, abortions occur between 40 and 60 days.

Males may have an enlarged scrotum with an accumulation of fluid in the tunica vaginalis and scrotal dermatitis.

The epididymis may be enlarged. Overall there may be a decrease in the volume of ejaculate with unilateral or bilateral testicular atrophy and irreversible sterility. Semen abnormalities include deformed acrosomes, swollen sidepieces, and immature sperm (up to > 90% of the sperm may be abnormal).

Diagnosis: Culture of the organism is the best means of confirmating the infection. Blood, urine, and semen can be used for culture. However, B. canis is a difficult organism to grow. Antibody titers to B. canis are not present until 8-12 weeks post infection therefore, serologic screening is of limited use during this period. Administering antibiotics can nullify any serologic results.

Treatment: B. canis is difficult to eradicate because the organism survives in an intracellular location. Treatment is expensive and often unsuccessful with relapses commonly occurring. In breeding kennels the infected dogs should be isolated and eliminated from breeding. Neutering and antibiotics are the best treatment to decrease the chance of infecting others via the genital secretions. The infection can persist in neutered animals but the risk of secretions is decreased. Single antibiotics will not work. A combination of doxycycline with streptomycin or gentamycin or tetracycline and aminoglycosides administered for 4 weeks has shown to be successful. With any treatment a follow up test should be performed at 1 month and 3 months post treatment to check for relapses.

Prevention of the disease can be done in a breeding kennel by instituting a strict quarantine until two serologic tests come back negative one month apart. Also, breeding animals should be tested 3-4 weeks before breeding.

Humans

B. canis can be transmitted to humans with contact with an aborting bitch or semen or urine of an infected male dog. People are normally resistant to B. canis therefore the infection is mild and often misdiagnosed. Some people may have fever, chills, fatigue, malaise, lymphadenomegaly and weight loss. A chronic undulating fever can occur with symptoms persisting for years either continuously or intermittently with alternating periods of normalcy between acute attacks. Rarely B. canis can cause endocarditis, meningitis, arthritis, hepatitis, orchitis and epididymitis in men and visceral abscesses.

Diagnosis in humans is made by blood culture and serology. Human antibodies to B. canis will react in serologic tests for dogs and do not cross react with B. abortus antibodies. In active infections, titers > 200 are found.

Treatment: A combination of doxyclycline and rifampin for 6 weeks is the treatment of choice.

Prevention: The organism can be transmitted in the saliva, urine, and vaginal discharge of the infected dog. Veterinarians must take caution and wear gloves when examining any dog with vaginal discharge and history of abortion. Veterinarians must also warn owners of the potential zoonotic risk to themselves and especially their children.

Dogs must be isolated from other dogs and humans during their treatment.

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