Overview

Canine brucellosis is a serious reproductive disease caused by the bacteria Brucella canis, which can affect dogs and sometimes wild canids. Brucella is a zoonotic disease, meaning humans can be infected, and is reportable in several states. Unfortunately, there is no definitive cure for canine brucellosis, and relapses are common. While still relatively uncommon, canine brucellosis may be increasing in high-risk environments such as breeding kennels where a lack of mandatory screening for incoming dogs contributes to its spread.

Cause and transmission

Dogs contract brucellosis through contact with the bacteria B. canis in contaminated reproductive fluids (e.g., vaginal discharge, semen, aborted material), urine, or contaminated surfaces. The highest risk comes from exposure to aborted materials. The bacteria enter the body through mucous membranes (e.g., mouth, vagina, eyes) and spread to the immune and reproductive systems. B. canis can also infect other organs, including the kidneys, eyes, spine, and brain. Once in the bloodstream, the bacteria can persist for months or even years.

While breeding dogs are at the highest risk, all dogs, including spayed or neutered ones, can be infected and develop clinical disease. Additionally, dogs can contract brucellosis from livestock-associated Brucella species (e.g., B. abortus, B. suis, B. melitensis) by ingesting raw meat, coming into contact with infected birth fluids, or exposure to contaminated environments. Farm dogs, hunting dogs, and those in rural areas are particularly at risk, especially if they scavenge or interact with infected livestock or wildlife. This article focuses on B. canis infections in dogs.

Clinical signs

The clinical signs of brucellosis can be absent or vague and nonspecific. Reproductive issues are the most common sign, and brucellosis should be considered in any case of reproductive problems:

• Females: Infertility, early embryonic death, late-stage abortion, or uterine infections (endometritis).
• Males: Infertility, enlarged or irritated scrotum, inflamed testicles, or testicular shrinkage over time.
• Non-specific signs: dry hair coat, decreased energy or appetite, eye issues, or spinal pain (diskospondylitis). 

Diagnosis

Diagnosing B. canis can be challenging since the bacteria can be shed intermittently in the bloodstream. Several tests are available, each with its limitations, so your veterinarian may recommend a combination of tests and multiple sample collections over time.

The previously popular Rapid Slide Agglutination Test (RSAT; D-TecÒ CB from Zoetis) has been discontinued, making testing for B. canis exposure more difficult. However, the Animal Health Diagnostic Center at Cornell University offers a new Canine Brucella Multiplex test, whichcombines multiple serologic tests (RSAT, AGID, and 2ME-RSAT) to improve diagnostic accuracy.False-negatives may occur in acutely infected dogs that may not have developed sufficiently high antibody titers during the first three weeks of infection.

Testing to detect B. canis bacteria includes bacterial culture and PCR. Submitting serial samples increases the likelihood of detecting bacteria. While bacterial culture is considered the "gold standard" for detecting B. canis false-negative results may occur because the bacteria might not always be present in the bloodstream at the time of testing. Additionally, B. canis is a fragile organism and may not survive transportation or storage after testing, resulting in a negative culture. In contrast, it can detect the bacteria even if it's no longer viable, though it still may miss intermittent shedding. Testing is most successful with aborted materials, as the bacteria are typically abundant in these tissues and vaginal secretions following an abortion.

Treatment

There is no official or completely effective treatment protocol for brucellosis. 

Treatment options may also depend on state guidelines, and your veterinarian should check with the state veterinarian before treatment. It is a reportable disease in several states where neutering or even euthanasia is required. 

Many regions do not attempt treatment in dogs and elect euthanasia either as a treatment choice or as a regulatory requirement based on the concern of zoonosis and the inability to treat and eradicate the infection. However, many challenge this approach as the zoonotic effect on humans is seemingly rare. 

If treatment is elected, it may include the following:

• Spaying/Neutering: This reduces bacterial shedding but does not cure the infection.
• Antibiotics: A combination of more than one antibiotic for several weeks is often used. However, there is no known best antibiotic or duration, and bacteria can persist inside cells and tissues even after bacteria in the bloodstream have resolved, which makes relapses common.
• Monitoring: Dogs treated with antibiotics must be screened periodically to test for recurrence.

Outcome

Information on the prognosis and response to treatment is limited as euthanasia is not uncommonly elected. Canine brucellosis is considered a lifelong infection in dogs because even after attempting treatment with spay or neuter and long-term antibiotic use, dogs may continue to shed the bacteria intermittently. Infected dogs are often not critically ill, but relapses are common if treatment is attempted. Monitoring for reinfection should be performed ongoing if treatment is elected. 

Zoonosis

B. canis is a reportable disease in some states, and people can be exposed to contact with an infected dog’s urine, reproductive fluids, and tissues such as aborted materials. While rare, it is underreported and can pose risks to immunocompromised individuals. Always use gloves and practice proper hygiene when handling potentially infected materials.

Prevention

Spaying and neutering dogs can reduce the risk of reproductive spread of B. canis and decrease shedding; however, it does not prevent non-sexual spread of the disease.

Strong biosecurity protocols can limit the risk of introducing brucellosis into breeding facilities:

• Testing animals, particularly those from high-risk areas, before introducing them to the general population in a breeding facility.
• Routine disinfection should be performed as B. canis does not survive long in the environment and is killed readily with common disinfectants.
• Breeding animals should be tested every six months or before every breeding for females. Infected animals should not be used for breeding.

Updated May 2025