Brucella canis: an underrecognized zoonotic threat at the dog–human interface

A new review in Pathogens argues that Brucella canis remains substantially underdiagnosed in people despite its established zoonotic potential. The bacterium is maintained primarily in dogs, but human infections can occur after exposure to reproductive tissues, blood, urine or other contaminated material. Because clinical signs are often nonspecific and routine brucellosis tests may fail to detect B. canis, the true burden of infection is still poorly defined.

B. canis differs from the better-known smooth Brucella species such as B. melitensis and B. abortus. It is a rough Brucella, and this biological difference has important diagnostic consequences: many serological assays used routinely for human brucellosis are designed for smooth lipopolysaccharide antigens and may therefore miss B. canis infection.

Dogs are the main reservoir

The bacterium is mainly associated with dogs, in which infection can cause reproductive disease, including infertility, abortion, epididymitis, orchitis and reduced litter size. Infected animals may also remain clinically normal.

Transmission between dogs is strongly associated with reproductive secretions, but bacteria can also be present in blood, urine and other body fluids. This means that breeders, veterinarians, kennel workers, laboratory personnel and owners handling infected dogs may all be exposed. The international movement of dogs adds another layer of concern. Infected animals can be transported while appearing healthy, allowing the organism to reach regions where canine brucellosis is not routinely considered.

Human disease is probably missed

Human B. canis infection can produce a wide range of symptoms, including fever, fatigue, malaise, headache, weight loss, lymphadenopathy and musculoskeletal pain. More severe complications have also been described, including endocarditis, osteoarticular disease and neurological involvement. None of these signs is specific to B. canis. The review therefore stresses that cases may be misclassified or remain unexplained unless clinicians know that the patient has had relevant contact with dogs.

The diagnostic problem is reinforced by the fact that some standard human brucellosis tests are poorly suited to B. canis. Culture remains useful but can be slow and hazardous to laboratory personnel, while molecular testing and species-specific serology are not universally available.

Breeding kennels are a particularly important setting

The highest-risk environments are those where many dogs are housed together and where reproductive material is handled regularly. Canine outbreaks in breeding establishments can persist because infected animals may remain bacteremic for prolonged periods and because reproductive losses may initially be attributed to other causes.

The authors argue that dog breeding facilities should therefore be viewed as an important One Health interface rather than solely as a veterinary reproductive-health issue.

No human vaccine and difficult control in dogs

There is currently no licensed vaccine for B. canis in dogs or humans. Control therefore depends on testing, biosecurity, management of infected animals and prevention of exposure to reproductive tissues and contaminated secretions. In breeding populations, identifying infected dogs is essential because treatment can be prolonged, relapses can occur and complete bacterial elimination is difficult.

The review also highlights the need for better coordination between veterinary laboratories, physicians and public-health authorities when human exposure is suspected.

A classic One Health blind spot

The main problem with B. canis is not that it is a newly emerging pathogen. It is that it can circulate at the dog–human interface while remaining poorly detected on both sides. Dogs may carry the bacterium without obvious signs, human disease is clinically nonspecific, and routine laboratory methods may not identify it.

The authors therefore call for greater awareness, improved diagnostic capacity and more systematic surveillance of canine brucellosis, particularly in breeding kennels and in dogs moving internationally.