Canine brucellosis is a contagious bacterial infection that can cause reproductive failure in dogs. The most common site of infection is the dog’s reproductive tract. However, the bacteria can affect other organs and cause illness in spayed or neutered dogs. Brucellosis is highly contagious among dogs and is a zoonotic disease that can be transmitted from dogs to people.
Since dogs are often in close contact with people, brucellosis is a significant public health concern. It’s important to know how to protect your dog and yourself from becoming infected. Read on to learn about the signs of brucellosis in dogs, how it’s transmitted between dogs, and ways to control the spread of infection.
What Is Brucellosis in Dogs?
Canine brucellosis is an infectious disease that is most commonly caused by the bacteria Brucella canis (B. canis), says Dr. Kara Kolster, DVM DACT. Several species of Brucella exist such as Brucella suis which commonly infects pigs, and Brucella abortus which infects cattle and bison. Dogs can become infected with B. suis from exposure to wild pigs.
B. canis was first identified in the United States in 1966. Since then, brucellosis has been reported worldwide. The World Organization for Animal Health considers it a priority disease because of its impact on public health, global trade, and economics.
The true rate of brucellosis in the U.S. is difficult to determine. Some reports suggest that the prevalence among dogs in shelters ranges from 0 to 8.6%. The disease can spread when dogs are relocated from areas with a higher incidence of brucellosis like the Southern states and Central and South America.
How Does Brucellosis Spread?
There are several ways that this infection disease can spread:
Between Dogs
Dogs can develop brucellosis through sexual transmission or more likely from contaminated body fluids like when they sniff urine or consume infected milk. Brucellosis can spread quickly among dogs in close quarters. The infection can result in miscarriage, stillbirth, or infertility.
Large numbers of B. canis are found in semen and vaginal discharge of infected dogs, as well as the fetus, placenta, and aborted tissue. “Organisms can be found in vaginal secretions for several weeks following an abortion, as well as in normal vaginal secretions during estrus and in milk during lactation,” Dr. Kolster says. “High concentrations of bacteria are also found in semen for months following infection, but lower concentrations may persist for years.”
B. canis can be transmitted through natural breeding and artificial insemination whether fresh or frozen semen is used. “Smaller quantities of B. canis are shed in urine, saliva, and nasal and eye secretions, as well as feces from intact or neutered animals,” she says. B. canis may also spread through inhalation, ingestion, genital contact, or wounds. Sometimes the bacteria can infect the eyes, heart, kidneys, and brain and cause problems depending on the organs involved.
From Dogs to Humans
Most human cases of brucellosis are caused by consuming unpasteurized dairy products or undercooked meat. Infections are usually the result of Brucella melitensis, a bacterium associated with livestock. The infection can lead to serious illness including fever, chills, enlarged lymph nodes, or an enlarged spleen.
Although rare, brucellosis can spread from dogs to humans. Among the most vulnerable are children and pregnant or immune-compromised individuals. In addition, breeders, veterinarians, laboratory workers, and kennel workers may be at increased risk if, for example, they have direct contact with an aborted litter, breeding dogs, or newborn puppies. Owners are less likely to encounter blood or vaginal discharge from an infected dog.
Symptoms of Brucellosis in Dogs
Given the severity of this disease, you might be wondering: what does brucellosis in dogs look like? Some symptoms differ between female and male dogs, but both sexes are susceptible to infection.
Female Dogs
Miscarriage during the last trimester of pregnancy is among the primary signs of brucellosis in female dogs, according to Merck Veterinary Manual. Abortions caused by brucellosis tend to occur at around 45 to 55 days. Oftentimes, dogs will produce a bloody or green-grey vaginal discharge for an extended period. Dogs may also produce discharge if they become pregnant again.
Exposure to aborted material and post-abortion discharge can put dogs at high risk of becoming infected. If the infection occurs soon after fertilization, the fetuses will die and be reabsorbed. Brucellosis tends to infect the uterus, leading to infertility or difficulty becoming pregnant. If the dog is pregnant, they may abort or give birth to stillborn puppies or weak pups. These pups won’t survive long but can still transmit brucellosis.
Male Dogs
The primary signs of infection are orchitis (painful swelling of the testicles), epididymitis (inflammation of the tube that carries sperm), and prostatitis (inflammation of the prostate). As a result, dogs may avoid mating or have difficulty urinating or defecating. They can develop an enlarged testicle or rash due to licking and self-trauma. Recurrent infections can cause the scrotum to harden and shrink. “Semen quality is decreased after infection and many males become infertile,” she says.
Both Sexes
Aside from reproductive effects, dogs may experience nonspecific signs such as lethargy, weight loss, exercise intolerance, fever, poor coat, or enlarged lymph nodes. Some dogs experience heart or neurological problems, uveitis (eye inflammation), discospondylitis (a bacterial or fungal infection of the intervertebral disks and vertebral bones), generalized fatigue, flu-like symptoms, or swollen lymph nodes. Others may be asymptomatic but continue to shed bacteria and infect other dogs, Dr. Kolster says.
How Is Brucellosis Diagnosed?
Brucellosis is diagnosed through laboratory tests. Dogs with signs of a reproductive disorder should be screened for brucellosis, Dr. Kolster says. Routine screening can help identify asymptomatic dogs before breeding takes place. Additionally, any dog or bitch being considered for breeding should first be screened and tested free of brucellosis prior to a breeding.
Testing for Antibodies
The most common tests for brucellosis are the rapid slide agglutination test (RSAT) and the immunofluorescence antibody (IFA) test which tests for antibodies to B. canis and can detect infections after a few weeks, Dr. Kolster says. Antibodies are proteins produced by the immune system that fight foreign substances like bacteria. The veterinarian can conduct the RSAT test in the office while the IFA test needs to be performed at a laboratory.
Both tests are designed to be very sensitive, meaning they’re unlikely to miss an infected dog. High sensitivity also means a high rate of false positive results if other bacteria are present. “Routine brucellosis testing in dogs does not identify B. suis, so additional testing should be done on any dog that is showing suspicious clinical signs with a negative B. canis test result,” she says.
If a dog tests positive based on RSAT or IFA results, this must be confirmed by more specific tests, such as agar gel immunodiffusion (AGID). “The AGID test is only performed at a few labs and is more time-consuming, so it’s not viable as a first step in diagnosis or as a routine screening test,” she says. The AGID can detect antibodies in animals between 12 weeks and 1 year after the infection.
Testing for Bacteria
Another option is to test for the bacterial organism itself using PCR testing, ELISA essays, and bacterial culture. These tests are susceptible to false negative results and may take several weeks to confirm the diagnosis. Accordingly, “dogs should be tested early enough to allow time for confirmatory test results prior to breeding, but not so early before a heat cycle that the dog could potentially be exposed between testing and breeding,” she says.
Testing recommendations are as follows:
- Stud dogs should be tested every 6 to 12 months or more frequently if they have a high risk of infection, such as dogs in a rescue shelter or breeding facility. Testing is also recommended for dogs with orchitis, epididymitis, or an unexplained drop in semen quality.
- Female dogs should be tested before each breeding and in cases of abortion or pregnancy loss
- New dogs to a kennel should be quarantined for 8 to 12 weeks and tested at the beginning and end of the quarantine period
- Dogs showing reproductive abnormalities and non-reproductive signs associated with brucellosis should be tested
- Dogs testing positive for brucellosis should be quarantined and tested, and new dogs should not be permitted
Treatment and Control of Brucellosis
Disinfectants like bleach and ethanol can kill B. canis on hard surfaces. However, the organism can remain viable on dog bowls and bedding for months, especially in cool conditions, Dr. Kolster says. If you’re handling infected dogs or aborted material, practicing good hygiene, wearing protective gloves, and sanitizing an area where a dog has whelped can help reduce the risk of exposure to B. canis.
Dogs who test positive for B. canis must be isolated and tested monthly. In multi-dog households and breeding kennels, dogs need monthly testing for at least three months until they all test negative for brucellosis. Some U.S. states have implemented mandatory reporting of brucellosis cases. Other states require brucellosis testing for interstate or international transportation of dogs to limit the spread of disease, Dr. Kolster says.
There is no cure for brucellosis and it’s very difficult to treat. Sometimes neutering or spaying an infected dog is recommended instead of euthanasia, along with putting them on long-term antibiotics. Often, dogs will continue to shed bacteria, especially when stressed, which can lead to a recurrence of disease. Despite antibiotic therapy, B. canis can survive inside the host animal’s cells and tissues, usually in the lymph nodes, spleen, and prostate.
If a breeding kennel has confirmed cases of brucellosis, euthanasia may be recommended. Dogs infected with brucellosis cannot be bred. “In some states, euthanasia or strict life-long quarantine is mandated by the health department,” she says. “Treatment of an individual dog diagnosed with brucellosis should only be attempted under the care of a knowledgeable veterinarian, with awareness of the public health risk and potential for further spread of the disease.”
If an owner declines euthanasia, their dog will need lifelong monitoring and treatment including sterilization, treatment with antibiotics, and isolation requirements. Canine brucellosis can have devastating consequences for the affected dog, as well as entire breeding programs. “Vigilance in testing, reporting positive cases to state authorities, and careful management of dogs imported from other states or countries can help prevent infection in dogs and people,” she says.