By Jai Diggs, DVM
Brucella is a non-motile gram negative coccobacillus. There are 6 types of Brucella, 4 of which have been shown to infect the dog B. melitensis, B. abortus, B. suis, and B.canis. Dogs can be mechanical or biologic vectors for transmission to humans and other animals, except for a B. canis infection which is species specific. The term Brucellosis is used when an animal has been shown to be infected with one of the Brucella strands.
Dogs can contract B. meletensis, suis and abortus infection; these types of infections can be contracted thru natural or experimental exposure. A natural infection occurs when the dog ingests contaminated milk, meat, or aborted fetuses or the fetal membranes of infected livestock. Dogs have the potential to infect cattle and humans.
Dogs that contract a B. canis infection; this type of Brucella infection is species specific (meaning that it only affects dogs) to the canidae family. Humans are usually accidental host, and infections are usually mild compared to humans infected with other Brucella species. Livestock, primates, and rabbits are quite resistant to this strand of Brucella.
Transmission of Brucella canis; the infection can occur readily across mucus membranes, causing dogs to be infected by oronasal (mouth and nose), conjunctival (inner eyelids) or vaginal exposure. Infection readily occurs when an uninfected bitch is bred to with an infected male. Males can also acquire the disease from females.
Clinical signs of Brucella; dogs without our clinical signs can harbor Brucella organisms for prolonged periods of time. The time from exposure to bacteremia (noticeable/detectable changes in the bacteria population in the blood stream) is usually 21 days. After the dog has become symptomatic, the bacteremia can become localized (affecting certain areas of the body), therefore causing continuous or recurrent infections that last for months to years. The bacteria can be localized to the prostate or epididymis (a tubular part of the male reproductive system responsible for carrying semen).These infection sites can serve as a source of widespread infection, if such male is actively used in a breeding program. Venereal transmission appears to occur most when an infected male is bred to a susceptible female and somewhat less often when susceptible males bred to infected females (but transmission still can occur this way).
In a kennel situation, a Brucella infected bitch that is aborting a litter is highly dangerous to a kennel that is Brucella free. Aborted placental tissues and fluids may contain large numbers of the organisms. Vaginal discharge from a bitch that has aborted a litter is typically rich in Brucella and should be handled with caution because they can be the source for rapid spread with in a kennel and because humans can catch this disease. Milk from a Brucella positive bitch may also be an abundant source for the bacteria. Blood transfusions can also be a vector for the spread of Brucellosis
Other clinical signs; generalized lymph node enlargement, discospondylitis (inflammation of vertebrae/ backbone with lytic lesions, typically causing back pain), conjunctivitis (swollen inner eyelids), Uveitis (inflammation of the iris and ciliary body, parts of the eye this makes the dog very sensitive to light), arthritis/polyarthritis (affecting more than one joint), poor hair coat, listlessness, abortion from 45to 59 days of gestation, resorption (a bitch will appear pregnant at about 5 weeks but then return to her normal size without aborting pups), infected bitches can carry pups to term and give birth to living and dead pups. Aborted pups are usually autolyzed (partially self-digested) brown to black appearance, brown to greenish gray vaginal discharge from the bitches vulva, and failure to conceive after several attempts.
There are a number of test currently available used to test dogs for Brucella. The most common test is the Card Agglutination Test and the Tube Agglutination Test. The Card test is usually the first test used. A negative card test is about 98% accurate, but if there is a positive card test it should be confirmed with a retest by the Tube Agglutination method.
Treatment for Brucella
-Medical suppression with tetracycline derivative antibiotics (I know of a lot people that have often thought they could cure Brucella with long term treatment of antibiotics. This doesn’t cure the infection in the dog it only decreases the levels of antibodies present to cause the test to give a negative reading, but if you take the dog off of the antibiotics and test it again it will read positive. The reason the antibiotics doesn’t work in these dogs is because Brucella has a very thick cell membrane that makes it very hard for the antibiotics to penetrate).
-Spaying and Neutering (Castration)
-Euthanasia (highly suggested in a kennel type environment)
Prevention of Brucella
-In a disease free kennel all new additions should be isolated for 1 month
-All new additions should have 2 negative tests 1 month apart
-Routine kennel disinfection
-Dogs in active breeding programs should be tested every 6 months
-No Brucella positive bitch should ever be bred, not even artificially
-If a dog in a kennel is positive all others should be tested and retested after 1 month.
-All repeat positive tested animals should be removed from the breeding program
-Most importantly eliminating the source of infection vaginal discharges, aborted material, semen, and urine
It is very important to remember that some test do not become positive for weeks to months after the infection. So, testing must continue on a monthly basis until all animals with a result have been removed.