The Great Imposter: Canine Brucellosis

What is Canine Brucellosis?

Canine brucellosis is a bacterial disease commonly associated with the breeding of dogs. It is caused by Brucella canis, a facultative intracellular pathogen (an infectious agent that goes inside of the cell and may be cultured in a laboratory). It has also been spotted infrequently in foxes and coyotes. The incubation period from exposure to infection and symptoms is believed to be about eight weeks.

The principal harm caused by B. canis is to induce abortions and stillbirths in pregnant dogs. In some cases, this may occur early in gestation and outwardly appear as a failure to conceive. Affected pups may be born weak and die shortly there after. Other pups may not show symptoms of Brucellosis until much later.

Brucellosis also affects male dogs causing abnormal sperm, epididymitis, scrotal edema or prostatitis (which can be painful). Common to both sexes are imflamation of lymph nodes (lymphadenitis), lethargy, appetite and weight loss. Other ailments thought related to brucellosis are more rare, including fever.

In fact, many dogs that are infected do not show any outward symptoms and those that do are often initially misdiagnosed. As brucellosis canis symptoms may indicate other diseases, it has been called "the great imposter."

Transmission

The bacteria B. canis may be shed (transferred) in the semen of infected males or by exposure to a fetus or fetal fluids. Vaginal discharge after stillbirth or abortion, or as is normal when females are in heat, are other avenues of contact.

Because brucellosis is a zoonotic disease, canine brucellosis may be passed to humans. Symptoms can appear as quickly as two weeks or as long as three months. Though human cases of brucellosis are reported to the Centers for Disease Control (CDC), the species causing the infection is not recorded. Symptoms are often reported as flu-like and antibiotics are the standard treatment.

Most researchers believe that human incidents of canine brucellosis are underdiagnosed and underreported for two reasons: the lack of a specific test for the infection in humans and symptoms common to many more prevalent conditions. Serosurveys conducted in the 1970s attempted to ascertain exposure in the general population but were inclusive.

However, a clinical report in 2005 indicated that one of the more recent veterinary tests available - the rapid screening agglutination test (RSAT) - was effective in diagnosing cases of human canine brucellosis. This report originated as a result of the infection in a 15-year old boy with oral lesions and a fever of 104º F.

(the boy was) empirically treated for 2 days with oral penicillin but this treatment was suspended because of an increase in levels of transaminase. After a week the patient worsened, with weakness, persistent fever, liver and spleen enlargement and submaxillary adenopathy, and was admitted to the hospital with a suspected diagnosis of cytomegalovirus (CMV) infection.

Source: Lucero et al, "Unusual clinical presentation of brucellosis caused by Brucella canis"

It was not until 10 days after hospital admission that a culture led to the correct diagnosis. Using the proper antibiotics, the fever was contained within 48 hours and other clinical signs improved significantly. Antibiotics were continued for another six weeks and the patient showed no signs of the infection in a follow-up eight months later.

It is believed that breeders, veterinarians and laboratory workers are the groups most at risk to B. Canis exposure. However, there have been a handful of other cases recently that were traced to dogs in the general population. In 2010, three adults and three children were infected after contact with a sick dog and her puppies. In 2012 in New York City, a three year old girl's infection was traced back to a puppy.

Outwardly, the number of human incidents seem insignificant. But as the 2005 report shows, unless the symptoms are severe, a connection to canine brucellosis may never be made.

Treatment

Like humans, dogs are treated for canine brucellosis with multiple antibiotics over a long period of time. However, unlike humans, there is no certainty that the disease will be completely eradicated. B. Canis may still be found in organs, lymph nodes, the prostrate and uterus even after treatment appears to be successful. Stress may later result in the reemergence of the infection. Males may be castrated (if not already done) to try to reduce transmission risk.

Unfortunately, the end result is often a recommendation that the dog be euthanized. This is particularly true of dogs used for breeding. Because of the risk of human infection, euthanizing may also be recommended for family pets. At the least, pets are to be kept quarantined from contact with other dogs and must be tested regularly after treatment with antibiotics.

References:

1. Lucero et al, "Unusual clinical presentation of brucellosis caused by Brucella canis", Case Report Journal of Medical Microbiology, vol 54 2005
2. Stella and Croney, "Brucella canis: Emerging zoonotic disease? Implications for commercial breeding kennels and public health", Center for Animal Welfare Science Purdue Extension Local Faces
3. Brucella canis Workgroup National Assoc. of State Public Health Veterinarians, "Public Health Implications of Brucella canis Infections in Humans", March 2012
4. A. Spickler,"Canine Brucellosis: Brucella canis", Iowa State CFSPH Technical Fact Sheet, April 2012
5. C. Mabray et al, "Best Practices for Brucella canis Prevention and Control in Dog Breeding Facilities", USDA APHIS publication October 2015