Lauren Harris, DVM, DACVECC
BluePearl Veterinary Partners – Clearwater, FL
I don’t know about you, but the last time I had Brucella on my differential diagnosis list as a cause for pyothorax was…well, never. However, two BluePearl hospitals diagnosed Brucella suis in dogs with pyothorax last year. Brucella suis has not been previously reported as a cause of pyothorax in dogs.
The first dog was a 10 to 12-year-old spayed female pitbull mix. She was found as a stray in Hawaii in 2011 and shipped to Michigan for spay and adoption. While her full history was unknown, she was suspected to be a pig-hunting dog based on her scars and tattoos. In 2013, she was diagnosed with idiopathic chylothorax. After surgery and pleuroport placement, she did well for two years without recurrence of pleural effusion. In November 2016, chylous effusion returned. After a month of steroid therapy, the effusion became serosanguineous and was submitted for bacterial culture. The culture detected Brucella suis. It is suspected that this dog contracted B. suis in Hawaii while pig hunting, and had a subclinical infection. The patient was started on a 6-week course of doxycycline and enrofloxacin, and is currently under a lifelong quarantine agreement with the Michigan State Health Department.
The second case was recently treated at BluePearl Tampa. This dog is a 6-year-old castrated male Catahoula leopard dog. The dog was recently adopted, and had a known history of feral pig hunting. In late May 2017, he was medically managed with antibiotics and chest tube placement in Texas for a pyothorax. In June of 2017, he was seen by the emergency service at BluePearl Tampa for increased respiratory effort. A pyothorax was diagnosed, and exploratory surgery was elected. At surgery, a large volume of purulent effusion was noted in the chest as well as a cranial mediastinal granuloma/mass. During cranial mediastinal mass removal, the brachycephalic trunk was inadvertently ligated, and subsequently repaired. During repair, the patient experienced cardiopulmonary arrest, but was successfully resuscitated. While in surgery, the Texas veterinarian previously treating the dog called to report that the dog was culture positive for Brucella suis. Humane euthanasia was discussed, but declined by the owner. After two days, the patient started to experience swelling of the forelimbs, ventral neck, and head. Cranial vena cava syndrome (secondary to cranial vena cava clot or stricture) was considered. Additional surgical intervention was discussed but declined. After one week in the hospital, the owner removed the pet from the hospital against medical advice and the patient was lost to follow up. The cranial mediastinal mass histopathology was suspicious for a necrotic thymoma. During the course of his hospitalization, nine BluePearl Tampa employees were directly exposed to B. suis, seven of which were prescribed the CDC’s recommended six-week prophylactic antibiotic combination of doxycycline and rifampin. At the time of this writing, one associate has tested positive for B. suis.
Brucellosis is an infectious disease caused by Brucella, a gram-negative coccobacillus that can infect a variety of animal species and humans. Several species of Brucella exist which are based on host preference: Brucella abortus (cattle), Brucella canis (dogs), Brucella melitensis (goats, sheep), Brucella neotomae (rodents), Brucella ovis (sheep), and Brucella suis and its biovars (pigs, cattle, hares, rodents, and wild ungulates). In the past few years, the incidence of B. suis in dogs in certain parts of Australia increased 17-fold. Brucella suis is much less commonly diagnosed in the United States; however, the USDA APHIS diagnostic laboratory (in Ames, Iowa) documented a few cases of B. suis in dogs in the Eastern United States in 2017.
In the United States and Australia, feral pig hunting has been identified as the principal risk factor for canine brucellosis due to B. suis. Other possible causes for exposure may include ingesting raw feral pig meat or being exposed to other dogs used for feral pig hunting. In rare cases, there is no known risk factor. Humans may be exposed to B. suis by coming in contact with bodily fluids of infected dogs (including urine, saliva, reproductive materials, respiratory secretions or body cavity effusions). Laboratory personnel, slaughterhouse workers, meat-packing plant employees, and veterinarians are at highest risk of exposure. Because these organisms are zoonotic and a threat to human health, B. abortus and B. suis are reportable to public health in all states.
Clinical signs of B. suis in dogs most commonly include: fever, orchitis/epididymitis, back pain, lameness, abortion, enlarged lymph nodes, lethargy, and occasionally vomiting. It is estimated that up to 40% of serologically positive dogs have a subclinical infection (showing no clinical signs of illness). While not previously reported, these two cases demonstrate that Brucella suis may be isolated in pleural effusion.
Brucella suis should be considered as a differential in any dog with a history of exposure to feral pig hunting, or to other dogs that have previously hunted. In any case where Brucella is being considered, individuals working with these animals or lab samples should use personal protection equipment including gloves, disposable gown, facemask and eye protection. The use of good personal hygiene is also of great importance. Extreme caution and care should be used when treating wounds, collecting blood or other tissue samples, neutering/spaying, or handling any reproductive tissues including fetuses of possibly infected dogs. The animal should be kept in isolation. Brucella can survive for months in the environment, but is inactivated with autoclaving, commonly used hospital disinfectants, and by direct sunlight.
In cases where B. suis is considered a potential diagnosis based on risk factors and/or clinical signs, testing is available. The USDA APHIS diagnostic laboratory recommends that canines with exposure to suspected B. suis be screened with a card test (slide agglutination test) for B. abortus as it cross reacts with B. suis. If the card test is positive, serology, culture, and PCR for B. suis at the Ames laboratory is recommended. It is important to note that patients that have been recently infected with B. suis organisms may be serologically negative, and should be re-tested in 6 weeks. Agar gel immunodiffusion (AGID) or slide agglutination testing for B. canis is commonly available at most reference laboratories; however, this test is specific for B. canis and does NOT cross react with B suis.
Given the zoonotic potential of B. suis, euthanasia of affected dogs is recommended, but not mandatory. If euthanasia is not elected, combination therapy with doxycycline and rifampin seems to be effective, when combined with surgical resection of infected tissues. Affected animals should be isolated from other animals, and this quarantine is for the life of the pet. Serum biochemistry should be frequently rechecked due to the potential hepatotoxicity of rifampicin. Response to treatment can be monitored with recheck serology.
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