| VIVO Infectious Diseases | Bacterial Diseases of Man and Animals |
Brucellosis in Dogs
Canine infections with Brucella abortus and melitensis have been reported, but dogs are generally considered resistant to infection with those species of Brucella, and those infections have typically been associated with close contact between dogs and infected cattle or small ruminants. There is, however, a species of Brucella named Brucella canis that commonly infects dogs and can uncommonly infect and cause disease in humans and other animals. This organism has a worldwide distribution and in some regions is increasing in prevalence. Due to its zoonotic potential, canine brucellosis is a reportable disease in some countries.
Clinical Disease
Canine brucellosis is predominantly a reproductive disease:
- Infection in females frequently results in abortion or birth of weak puppies that often do not survive. In addition to the classical picture of abortion, infection often leads to infertility.
- B. canis infection of males often leads to infection of the testes and epididymides, sometimes resulting in a painful, swollen scrotum and scrotal rash. Small atrophic testes are commonly seen in longstanding infection.
In both males and females, infection with B. canis commonly results in enlarged lymph nodes and non-specific systemic illness, although usually without fever. Importantly, a significant fraction of canine brucellosis cases are asymptomatic, making routine diagnostic testing important, especially in breeding kennels.
Transmission of Infection
Infected dogs have high concentrations of B. canis in vaginal discharges, particularly following an abortion, and in semen. The organism is also present in large numbers in aborted fetuses and placentas, and can also be present in urine. The most common routes for transmission are by oral or respiratory exposures, for example by licking or sniffing and being exposed to vaginal fluids. Venereal transmission is also efficient either from contaminated semen (male to female) or from exposure to vaginal secretions (female to male). Finally, abortions in particular result in significant contamination of the environment with B. canis, and transmission can also occur by exposure to bedding or fomites.
Diagnostic Testing
The gold standard for diagnosis of B. canis infection, as for all types of Brucellae, is isolation of the bacteria in culture. However, this technique is not commonly employed as it requires BSL3 laboratory facilities due to the biologic hazards involved.
Testing for antibodies to B. canis in serum is the most commonly used diagnostic test for canine brucellosis. Several serologic tests have been developed, with the most commonly used a rapid slide agglutination test and agar gel immunodiffusion. Significant problems with these tests are false negatives early in the course of infection and false positives due to cross reactions from previous infections with other bacteria.
Molecular diagnostics such as polymerase chain reaction are increasingly utilized for to detect the DNA of B. canis in blood.
Control of Infection
There are no vaccines available for control of canine brucellosis. A number of antibiotics (e.g., doxycycline, minocycline) have activity against B. canis in culture, but have proven unreliable in clearling infection in dogs. Thus, antibiotic therapy of infected dogs is not generally encouraged because of the high incidence of relapse after treatment. A key point about canine brucellosis is that infected dogs should be considered to be infected for life and to pose a continued threat for infection of other dogs and humans.
Two fundamental recommendations can be made to breeding kennels:
- Do not introduce new animals from the outside without first testing them, usually before and after a period of quanantine.
- Institute a policy of routine serologic testing (e.g., every 6 months) of all dogs to allow early detection of infection.
Human Infections
Human infection with B. canis is relatively rare and usually an occupational risk for veterinarians and dog breeders. Clinical signs of infection in humans are often vague and non-specific, but infection can result in serious disase of the heart, skeletal system or brain. Standard precautions such as wearing gloves and handwashing are recommended, especially when handling dogs that have aborted or birthed weak puppies.
References
Dadar M, Fakhri Y, Shahali Y, Tittarelli M, Sacchini F, De Massis F. Global epidemiology and diagnostic insights into canine brucellosis: A comprehensive meta-analysis and meta-regression. One Health. 2025 Sep 29;21:101225.
Santos RL, Souza TD, Mol JPS, Eckstein C, Paíxão TA. Canine Brucellosis: An Update. Front Vet Sci. 2021; 8:594291.
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Updated February 2025. Send comments to Richard Bowen: rabowendvm@gmail.com