Organisms of the genus Brucella are small,non-motile, Gram-negative coccobacilli capable of causing disease in man, dog, cattle, sheep,goats, swine, and various wildlife species.
Brucellosis in humans is most commonly a food-borne disease caused by Brucella melitensis, as seen in California (Chomel et al., 1994b).The most common source of human infection is unpasteurized milk products. Dogs can be
infected by several species of Brucella, including B. abortus and B. melitensis, and play a role in the dispersion of these organisms between farms, potentially being a source of human contamination. Infection of dogs with B. abortus has been reported in experimental and field studies (Forbes, 1990). Evidence exists for transmission from cattle to dog by ingestion of infected reproductive tissues. Additionally, it seems likely that infected dogs can transmit B. abortus to naive cattle. At present, the zoonotic potential of B. abortus transmission between dog and man appears limited in most developed countries. Conversely, dogs are the main reservoir of B. canis, which is
pathogenic to humans (Johnson and Walker, 1992; Kerwin et al., 1992). In domestic and wild canids, B. canis is transmitted primarily by ingestion or inhalation of aerosolized postabortion material, but venereal transmission
is also reported (Johnson and Walker, 1992).
Human infection by B. canis is not common, but at least 30 human cases have been reported (Lum et al., 1985). In Argentina, an outbreak involved six persons (three children and three adults), and a bitch and three puppies which had close daily contact with the family (Lucero et al., 2010). The clinical symptoms of the index case led to an erroneous diagnosis and the infection would have gone undiagnosed if culture had not been positive.
Symptoms of B. canis infection in humans are largely non-specific and include fever, splenomegaly, malaise, myalgia, headache, and anorexia (Lum et al., 1985). Septicaemia has been reported in 50% of patients (Rousseau, 1985). Though most cases respond well to antibiotic therapy, as many as 3% of treated patients may die from endocarditis or other complications (Rousseau, 1985). In dogs, B. canis infection is characterized by prolonged bacteraemia and reproductive failure in both males and females. Transient lymphadenopathy and fever are occasionally detected in early stages of infection (Johnson and Walker, 1992). In the pregnant bitch,
B. canis causes embryonic or foetal death, or abortion, by colonizing the placental epithelial cells. Live-born puppies infected in utero do not usually survive to weaning (Carmichael and Greene, 1990). In the male dog, B. canis causes epididymitis and infertility as a result of abnormal spermatogenesis (Johnson and Walker, 1992). In both genders, infection is largely asymptomatic and often remains undetected unless the animal is bred. Occasionally complications arise, including discospondylitis, uveitis, meningitis, glomerular nephritis,
and draining skin lesions. A diagnosis of brucellosis can be made by either blood culture or serology. In the case of serology, specific B. canis antigen should be used, as serological tests for diagnosis of ruminant or swine brucellosis do not cross-react with this antigen (Polt et al., 1982).
Treatment is based on the use of doxycycline and an aminoglycoside (streptomycin, gentamycin, or netilmicin) for 4 weeks followed by doxycycline (200mg per day) and rifampin (600–900mg per day) orally for 4–8
weeks (Tan, 1997).