Brucellosis
Brucellosis is a contagious zoonotic disease (affects animals and people) caused by a group of bacteria known scientifically as the genus Brucella. The disease in ruminants is also known as contagious abortion or Bang’s disease.
Brucella abortus primarily affects cattle, bison, deer and elk. Sheep, goats, horses and dogs are also susceptible. Brucella suis affects mainly swine. Brucella ovis and Brucella melitensis affect sheep and goats. Brucella canis affects dogs.
Brucellosis infections in cattle and swine pose a serious threat that could result in significant consequences for domestic and international movement of livestock. The United States Department of Agriculture Animal Plant and Health Inspection Services administers a cooperative state-federal brucellosis eradication program for these species. Due to the disease eradication efforts implemented under this program, and support and participation of livestock producers, Minnesota along with 49 other states, Puerto Rico and the U.S. Virgin Islands is classified as cattle and swine brucellosis free.
Minnesota administers brucellosis free certification programs for sheep and goats.
Once thought to be a rare disease, canine brucellosis has started to garner the attention of animal and human health agencies both in the United States and internationally. Difficult to diagnose, it is believed that the prevalence of disease has long been underestimated, and B. canis may pose a larger threat than first thought. Canine brucellosis disease control efforts in Minnesota include mandatory brucellosis testing for adult, intact dogs distributed by licensed commercial breeders, and a canine brucellosis policy that requires isolation or euthanasia of any dog confirmed to be infected.
Transmission
Brucella concentrates in the placenta, fetus, and fetal fluids, as well as vaginal discharge. These infected tissues serve to transmit the disease to other animals that may have direct contact with or ingest them. Transmission through broken skin is also possible. The bacteria can be spread by people, equipment, and through shared feed and water.
Bacteria can be shed in milk, semen, urine or other reproductive tract discharges, saliva, and nasal and eye secretions for several weeks or months following infection. Intermittent shedding can occur for years. The bacteria have also been known to survive for years in the environment in conditions of high humidity, freezing temperatures and/or limited sunlight.
Diagnosis
Many infected animals do not show outward signs of disease. When present, signs vary by species and individual animal. Signs may include reproductive disease including abortions, stillbirths, decreased milk production, birth of weak offspring, inflammation of the male reproductive organs, and sperm abnormalities. Animals may also present with weight loss, swollen joints and tendons, diseases of the eye, and inflammation of the spinal column.
Multiple serologic tests are available that test for antibodies produced by the animal’s immune system in response to an infection. Because of the potential for false results, positive tests are confirmed with additional testing to identify the bacteria. Field-side tests are readily available for use in livestock; however these tests do not detect infection with B. canis or B. ovis. Diagnosis of canine brucellosis must be done with agent specific testing.
Treatment
Brucellosis is not a curable disease in any animal. No treatment is certain to eliminate Brucella infections. Infected cattle and pigs are a dangerous source of infection and are depopulated as part of the United States Department of Agriculture’s Brucellosis Eradication program. Infected dogs can spread bacteria through body fluids, even after sterilization surgery and can infect both dogs and humans without ever showing clinical signs of disease. In Minnesota, infected dogs are required to be permanently isolated from other dogs not known to be affected or euthanized.
Human risk
Humans can become infected by handling infected animals or their reproductive or other bodily fluids, ingesting organisms, or by contamination of mucous membranes and abraded skin. Bacteria can survive in raw milk, but this serves as an unlikely source of infection due to routine milk testing and pasteurization. Immunocompromised people, the young and elderly, and people who are pregnant are most at risk of severe disease if infected. Clinical signs in people include recurring fever and other flu-like signs, spontaneous abortion, joint and heart infection, and reproductive disorders.
Prevention
Infection can be controlled with rigorous implementation of sanitation and infection control measures coupled with testing and subsequent isolation or euthanasia of infected animals. Special care and cleaning should be focused in animal birthing areas. Commercial vaccines are available for cattle, sheep and goats, but not dogs. Dogs imported from high-risk areas should be screened for the disease prior to resale/adoption or breeding.
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