Brucellosis is caused by a different member of the Brucella family from the one causing the disease we more commonly associate with cattle.
Dogs are infected by Brucella canis — the disease is passed dog to dog via reproductive fluids. This is very different from the serious cattle-human disease brucellosis, caused by Brucella melitensis, which infects people who drink infected milk.
Brucellosis in dogs most commonly causes abortion in females or testicular swelling in males. In rare cases it may also infect the intervertebral discs (causing a condition known as diskospondylitis) or the eye, causing iritis.
Signs of brucellosis in the dog are mostly associated with infertility and reproductive problems.
Females used for breeding may have difficulty falling pregnant, and if they do conceive, they frequently abort the puppies toward the end of the pregnancy. Puppies that survive are weak, do poorly and often die in the first few days of life.
Male dogs with brucellosis also suffer from infertility, but largely because of inflammation of the testicles. The scrotum becomes obviously swollen, and some dogs give themselves skin infections from constant licking.
Brucella canis invading the intervertebral discs is one cause of the painful condition diskospondylitis. Similarly, it occasionally infects the eye, causing inflammation known as iritis.
In the United States, 1–6% of dogs test positive for brucellosis, which means they have been exposed to the bacterium, but it has not necessarily made them ill.
The infection is passed in reproductive fluids and the transmission is dog to dog. Occasionally, lab workers, or people who have handled aborted puppies, can pick up infection and should be careful to wear gloves and a mask when handling such material.
There is a blood test for brucellosis that shows if the dog has been exposed to Brucella canis.
A diagnosis depends on 2 positive samples taken 2 to 4 weeks apart. It can be difficult to culture the bacteria from tissue samples since Brucella is easily killed by the presence of carbon dioxide.
Both tests, blood and culture, can yield false negatives and false positives.
A long course of antibiotics from the oxytetracycline family is required; however, relapse is common after the antibiotic finishes, so two 3-week courses are often prescribed, with a gap of a week or two in between.
Dogs with physical signs such as orchitis or repeated abortion should be neutered as they pose a risk to other dogs and are unlikely to be cured with antibiotics.
Although screening is not common, it is wise to breed only from dogs that have had 2 negative Brucella blood tests. Also, Brucella-positive animals should not be used for breeding, especially as they pose a risk to their partner. They should be neutered so as not to infect other dogs.
- “Bacterial diseases.” Greene. Textbook of Veterinary Internal Medicine. 5th edition. Ettinger. Publisher: WB Saunders.
- “Genital infections and transmissible venereal tumors.” Nelson & Couto. Essentials of Small Animal Internal Medicine. Publisher: Mosby.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.