The causative agent of brucellosis are gram-negative, aerobic bacilli of the genus Brucella. In Germany, brucellosis in cattle, pigs, sheep and goats is notifiable upon suspicion. The disease occurs in both animals and humans. Several Brucella species are known, including B. canis (canine brucellosis), B. abortus (bovine brucellosis), B. melitensis (ovine and caprine brucellosis), B. ovis (brucellosis in rams, infectious epididymitis, also notifiable upon suspicion) and B. suis (porcine brucellosis). Host-specificity of Brucella species is only limited.
Brucella canis is transmitted genitally or via the oral route by latently infected animals. After 2 to 4 weeks, bacteraemia develops. In pregnant female dogs, there may be abortions in the last trimester of gestation or weak puppies are born. Male dogs suffer from inflammation of the testicles and epididymis and can become infertile. A rare sign of Brucella canis infection is discospondylitis, so if there is pain in the spine and lameness, especially in dogs from Southeastern Europe, this infection may be an important differential diagnosis.The main signs of brucellosis in ruminants are abortions, birth of weak animals, inflammation of the testicles and epididymis, and infertility. In humans, the infection leads to fever, fatigue, night sweats, headaches and feelings of cold. The occurrence of cases in humans is always related to the disease being present in domestic or wild animals. Apart from direct animal contact, routes of infection also include the consumption of insufficiently heated food (e.g. raw milk or raw milk cheese) obtained from infected animals.