Members of the genus Brucella exist as intracellular pathogens in mammals. They do not exist as commensal species (those which derive a benefit from a host) nor are they found free-living in the environment. Although they can be recovered temporarily from environmental samples associated with infected animals, this is not important since direct or close contact is required for transmission.
The Brucella genus is usually divided into virulent (B. abortus, B. melitensis) and low pathogenic (B. canis, B. ovis). For the virulent strains, transmission primarily occurs through fluids or tissues associated with the birth or abortion of infected fetuses or offspring through milk. In stud males and bitches, the disease also causes sterility, a factor that causes significant economic losses in commercial kennels.
Venereal transmission is an important route of infection for B. canis, B. ovis, and B. suis. B. canis can also be shed in urine, milk, nasal secretions, and saliva, and has also been recovered from feces.1Brucella canis
is responsible for causing the zoonotic disease known as brucellosis. People can acquire this disease upon contact with infected dogs.
Source: CDC/ Dr. Todd Parker. Ph.D.
The organism is engulfed by macrophages and initially transported to lymph nodes where it replicates within lymphocytes for an indefinite period of time, then it is distributed to different organs of the reticuloendothelial system . Antibody titers rise after initial infection and fall as the number of bacteria in the bloodstream decreases. However, decreasing serum antibody titers do not indicate clearing of infection from the body.2 With the development of an effective body response, the bacterial proliferation is controlled and the bacteria are gradually eliminated. Nevertheless, the bacteria may persist in their host cells for months or even years and recommence replication if the activity of the immunologic control mechanism declines.3
The organs most commonly affected in male dogs are testicles and epidydimes (portions of the seminal tubes immediately attached to the testicles), causing inflammation, dermatitis, and infertility. The organism can be recovered from the testicles within five weeks of infection. Brucella canis has also been reported as a cause of uveitis, meningitis, diskospondylitis, glomerulonephritis, osteomyelitis, pyogranulomatous dermatitis, and cystitis.
B. canis is highly specific to dogs and has not been observed in other animals. Nevertheless, the bacterium has the ability to infect humans. Because of the low number of reported human cases, it has been proposed that the bacteria are less infective for humans than are the classical species B. melitensis, B. abortus, and B. suis. However, this may be a misconception. In the last decade, there has been a rise in the detection of human infections due to B. canis. Therefore, it may be that B. canis has an infectivity similar to that of the other zoonotic brucellae but has the potential to produce no symptoms for prolonged periods by using a stealth strategy.4
- Pathogenesis of Bacterial Infections in Animals edited. Glenn Songer, Carlton L. Gyles, John F. Prescott, Charles O. Thoen
- Canine and feline theriogenology. Shirley Dianne Johnston, Shirley D. Johnston, Margaret V. Root Kustritz, Patricia Schultz Olson
- National Institute of Allergy and Infectious Diseases, NIH: Volume 2. Vassil St. Georgiev, Anthony S. Fauci, M.D. (2009)
- Brucella canis Is an Intracellular Pathogen That Induces a Lower Proinflammatory Response than Smooth Zoonotic Counterparts
Carlos Chacón-Díaz,a Pamela Altamirano-Silva,a Gabriela González-Espinoza,a María-Concepción Medina,b Alejandro Alfaro-Alarcón,c Laura Bouza-Mora,d César Jiménez-Rojas,b Melissa Wong,a Elías Barquero-Calvo,a,b Norman Rojas,a Caterina Guzmán-Verri,a,b Edgardo Moreno,corresponding authorb,e and Esteban Chaves-Olartecorresponding authora,b Infect Immun. 2015 Dec; 83(12): 4861–4870.