CONDITION
Brucellosis in Dogs
Brucellosis in dogs is a bacterial infection caused by Brucella canis, an organism that tends to settle in the reproductive organs and lymph nodes. The infection spreads between dogs through breeding, contact with infected reproductive fluids, or occasionally through contaminated environments. It can persist for months or years without obvious signs in some animals. Owners often encounter this condition in one of several ways: difficulty achieving pregnancy despite repeated breeding attempts, unexpected loss of a litter in mid- to late pregnancy, or discharge from the reproductive tract that prompts investigation. In other cases, the infection is identified through screening before breeding or during routine health checks. Some dogs may show subtle signs such as lethargy, slightly enlarged lymph nodes, or joint discomfort, though many appear entirely well. This page explores the signals that may prompt investigation, the mechanisms by which the infection affects the body, the tests used to identify and monitor it, and the approaches taken to manage it in affected dogs and breeding populations.
Why this matters now
Brucellosis tends to surface in dogs that are part of breeding programmes or have been used for breeding, though infection can occur at any age once an animal becomes sexually mature. The condition is often identified when reproductive performance declines or when pre-breeding screening is carried out in kennels or breeding establishments. Dogs acquired from environments with multiple animals or uncertain health histories may carry the infection without having shown any signs.
The infection typically establishes itself quietly, often persisting for months or years without prompting investigation. In some dogs, the first observable event is reproductive failure—either difficulty conceiving or loss of a pregnancy—whilst others may develop intermittent signs such as mild lethargy or joint discomfort that come and go. The course varies considerably between individuals; some remain largely asymptomatic whilst others show more persistent, though still subtle, patterns over time.
Signals & patterns
Early signals
Difficulty achieving pregnancy
Repeated breeding attempts that do not result in conception may be the first indication that something is affecting reproductive function. This pattern can be difficult to interpret without investigation, as many factors influence fertility.
Subtle lethargy or reduced stamina
Some dogs may seem less enthusiastic about activity or tire more easily than usual, though the change is often mild and can be mistaken for normal variation in energy. This sign is non-specific and easily overlooked.
Slightly enlarged lymph nodes
Lymph nodes, particularly those beneath the jaw or behind the knees, may feel a little larger than expected during routine handling. The change is often subtle and may not be accompanied by any other obvious sign.
Intermittent stiffness or joint discomfort
Occasional reluctance to jump, climb stairs, or move freely can occur, often affecting one or more joints. The discomfort may come and go, making it difficult to pin down a clear pattern without further observation.
Later signals
Loss of pregnancy in mid- to late gestation
Absorption of developing puppies or late-term miscarriage may occur, sometimes with little warning. Discharge from the reproductive tract may be noticed around the time of loss.
Persistent or recurring discharge
Fluid or mucus from the vulva or prepuce that continues beyond what would be expected after oestrus or mating can prompt investigation. The discharge may be intermittent and vary in character.
Testicular changes in male dogs
One or both testicles may appear swollen initially, then shrink over time, becoming smaller and firmer than usual. The change may develop gradually and can be painless, so may not prompt immediate concern.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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