Preventing transmission of Brucella canis is compatible with a community engaged risk reduction approach. Risk reduction strategies that recognize the importance of the human animal bond and have additional benefits for canine and human health are more humane and more effective than the historically recommended management practice of screening testing, report, and euthanize (test and cull). Increasing access to veterinary care is a solution that creates opportunity for information sharing while dramatically reducing risk, increases willing participation in risk reduction, and supports the value humans place on animal lives. Spay / neuter is more likely to reduce risk of Brucella canis transmission than any other intervention.
Brucella canis, a bacterium that primarily infects dogs, is not a novel pathogen. No vaccine exists to prevent infection. Canine brucellosis is a disease that is found all over the world. The CDC has described infections with Brucella canis as being endemic to North America. The biologic, scientific, and human factors described here combine to make it unlikely that canine brucellosis will be eradicated.
Disease caused by Brucella canis is uncommon in both dogs and humans. Even though many humans live in very close contact with dogs, infection with Brucella canis has been diagnosed in very few humans. Human infections with Brucella canis are usually milder than infections with other Brucella species[1]. While a small number of unusual cases have been reported, natural infections in humans have mostly led to symptoms that resolved quickly with treatment. Human infections from all species of Brucella are reportable in all 50 states. For dogs, positive tests for Brucella canis are reportable only in some states and response to positive testing varies by state as well.
Transmission of Brucella canis requires close contact with tissues or fluids from an infected dog who is currently shedding the organism. Transmission between dogs happens primarily through breeding or contact with reproductive fluids or tissues. Some human infections have been associated with laboratory exposure to the cultured organism but most infections in humans have been associated with contacting birthing fluids or tissues (such as aborted fetuses or placenta). Because of this, risk is present and should be mitigated anytime a dog is whelping, especially in a home setting[2]. Providing access to veterinary care creates opportunities to provide information about minimizing risk of transmission from breeding and whelping.
The organism does not persist long in the environment so transmission is more likely from direct intimate contact. As such, other than intentional breeding, infectious transmission between dogs has been reported to occur most commonly in small geographic pockets. (i.e. a neighborhood rather than a larger geographical area such as a county or state).
Risk of transmission from dogs to both dogs and humans is lowered substantially by spay and neuter. Surgical sterilization removes the tissues of affinity, the behaviors (breeding, mating), and the resulting pregnancies and births that have the greatest potential to transmit disease. Organisms have been found to be present in urine, most likely as the result of vaginal discharge or semen mixing into the urine stream. While there has been concern that some organisms may remain in the prostate even after neutering, urine from spayed or neutered dogs would be expected to have a substantially lower quantity of bacteria, if present at all. There are no reports in the literature of Brucella canis infection in humans associated with a spayed or neutered dog even though millions of households full of people live closely with dogs that are spayed and neutered. Sixty-five million households in the U.S. report having a dog while even the lowest reports estimate that over 50% of all dogs in homes in the U.S. are spayed or neutered.
A test and cull approach is commonly recommended without either recognition of the significant challenges associated with screening testing for brucellosis in dogs or acknowledgement of the lack of efficacy of test and cull approaches in companion animals where the human bond is present. Effective brucellosis control cannot be achieved by individual dog testing [2]. Even with screening testing many infections will not be detected [3]. The puppy associated with one of the most commonly cited case reports on risk of human infection tested negative on a screening test so would not have been identified using a screening or test and cull protocol. A blood sample from that puppy was only cultured with a positive result after it was recognized that a child in the home was infected. A second puppy from the same litter, reported in the same paper, tested positive but recommendations to euthanize the puppy were declined and the owners declined testing for themselves as well [3].
To be effective, control measures must acknowledge the impact of human behavior. Mandatory reporting for a disease of companion animals, in a test and cull (or life-long quarantine) context, may actually decrease willingness to engage with public health systems, limiting the ability to recognize disease and understand prevalence and incidence of the disease [4]. “Recognize and euthanize” policies have limited efficacy in animal welfare settings where maximizing life-saving potential is prioritized. Likelihood of testing falls, which may actually increase risk, given human reluctance to risk lethal consequences that do not value the importance of the individual animal and the human-animal bond. Even where testing is enforced, compliance may be poor and the small theoretical reduction in risk that might be achieved by test and cull is not worth the substantial loss of life for dogs and resource drain on animal welfare organizations. In addition, resources directed to a reactive test and cull policy are directed away from actual prevention.
Improving access to veterinary care will improve One Health outcomes, utilize resources effectively, increase community engagement and participation in risk reduction, and substantially lower risk by providing care that is already being requested by the community. In contrast, relying on screening testing and euthanasia (or quarantine) puts an undue financial and emotional burden on animal welfare organizations, expending large sums of money while not effectively reducing risk, and has a negative impact on human mental and emotional health (personal communications). We cannot eliminate risk entirely and still have the benefit of canine companions, but we can substantially mitigate the risk without causing harm.
Sandra Newbury, DVM, Dip. DABVP
(Shelter Medicine)
Director – UW Shelter Medicine
Associate Professor
Department of Medical Sciences
University of Wisconsin – Madison
School of Veterinary Medicine
https://www.uwsheltermedicine.com/
Kate F. Hurley, DVM, MPVM, Dip. ABVP (Shelter Medicine)
Director, Koret Shelter Medicine Program
Center for Companion Animal Health
UC Davis School of Veterinary Medicine
www.sheltermedicine.com
Aleisha Swartz, DVM
Shelter Medicine, Department of Medical Sciences
University of Wisconsin – Madison
School of Veterinary Medicine
https://www.uwsheltermedicine.com/
Veterinarian, Rural Area Veterinary Services
Humane Society of the United States
GOALS
These identified goals guided our collaborative work on this document.
With realization that we cannot identify every case or eradicate the disease:
- Minimize risk of transmission to humans.
- Minimize risk of transmission to dogs.
- Improve community animal health overall.
- Improve One Health outcomes.
- Effective use of limited or finite resources.
- Maintain a life-saving approach that supports the human animal bond.
- Avoid placing economic burden on any one community, group, or individual to cover costs of surveillance.
- Recognize significant negative consequences and avoid barriers to community engagement and development of knowledge.
- Avoid negative impacts to human mental health and well-being (pet owners, vets, shelter and rescue workers) from a test /recognize and euthanize policy.
References
[1] CDC. Clinical Overview of Brucellosis. Brucellosis 2024. https://www.cdc.gov/brucellosis/hcp/clinical-overview/index.html (accessed July 9, 2024).
[2] Hubbard K, Wang M, Smith DR. Seroprevalence of brucellosis in Mississippi shelter dogs. Preventive Veterinary Medicine 2018;159:82–6. https://doi.org/10.1016/j.prevetmed.2018.09.002.
[3] Dentinger CM, Jacob K, Lee LV, Mendez HA, Chotikanatis K, McDonough PL, et al. Human Brucella canis Infection and Subsequent Laboratory Exposures Associated with a Puppy, New York City, 2012. Zoonoses Public Health 2015;62:407–14. https://doi.org/10.1111/zph.12163.
[4] Moore TS, Lancaster A, Nelson J, Sanders J, Johnson M, Moore A, et al. Notes from the Field : Multidisciplinary Approach to Investigating Brucella canis Exposures — South Carolina, September 2023. MMWR Morb Mortal Wkly Rep 2024;73:581–2. https://doi.org/10.15585/mmwr.mm7325a3.