It’s not every day that doctors see a Brucella infection among their patients. The disease is rare in the United States, with only about 120 cases annually. But when brucellosis is suspected, it’s vitally important to order the right tests to diagnose and treat the disease promptly with appropriate antibiotics.

But, before the tests are ordered, it is crucial to ask patients the right questions. Their health could depend on it. Those who don’t receive treatment for brucellosis can develop serious disease that can affect their lives and persist for years.

Although brucellosis is mainly a bacterial disease of animals, several species of Brucella bacteria are known to cause disease in humans. Because the diagnostic test and treatment vary, it is important to identify not only whether a patient is infected with Brucella, but also what kind of Brucella is causing disease.

Each species of Brucella has distinct risk factors. When brucellosis is suspected, getting a thorough medical history is an important first step because symptoms can develop anywhere from five days to six months after exposure.

Diagnosing brucellosis cannot be done by symptom presentation alone because initial symptoms are nonspecific and resemble those of other febrile illnesses. A person who is infected with Brucella typically presents with a history of fever; sweats; malaise; anorexia; headache; fatigue; and muscle, joint, or back pain.

About 70 to 75 percent of U.S. brucellosis cases reported annually to CDC are due to the bacterial species Brucella melitensis and Brucella abortus. Many of these cases are associated with consumption of unpasteurized dairy products — such as raw milk and cheese made with raw milk — during international travel to places where brucellosis is endemic in animals. Although acquired outside the United States, these cases are not diagnosed until after the patient has returned home, due to brucellosis’ long incubation period.

In the United States, 25 to 30 percent of brucellosis cases are due to Brucella suis and almost all are diagnosed in people who hunt and slaughter feral swine. People usually become infected through contact with blood and fluids from infected swine while dressing the carcass. However, keep in mind that dogs can contract brucellosis from feral swine and they can then spread the infection to people.

Although less common in humans, Brucella canis is found in dogs all over the world, including the United States, and generally causes mild illness in people.

Finally, people can become infected with Brucella RB51, a strain of Brucella abortus that is used to vaccinate cattle in the United States and other parts of the world. Although RB51 was developed to be less pathogenic, it can cause disease in humans. Human cases of RB51 are often associated with needle-stick exposures while vaccinating cattle, and cases are usually veterinarians or veterinary technicians.

Human cases in 2017 linked to raw milk
Although very rare, the CDC has received notification of two confirmed human infections with RB51 brucellosis associated with consumption of raw milk in the United States this year, emphasizing the need for healthcare professionals to ask patients whether they have consumed raw milk or other unpasteurized dairy products.

Most clinical diagnostic laboratories are able to run serologic tests, which detect an antibody response to most of the Brucella species. However, Brucella canis and Brucella RB51 won’t show up on serology, so cultures are needed to confirm the infection. State health departments can provide assistance in finding laboratories with culture capabilities. They can also guide physicians and assist in determining the appropriate route of sample submission for a proper diagnosis.

Always remember to inform the lab that brucellosis is suspected when submitting a sample. This will ensure that the lab staff will take appropriate precautions when performing tests and prevent additional exposures to the bacteria.

Treatment for brucellosis is typically a combination of doxycycline and rifampin for at least six weeks. However, Brucella RB51 is resistant to rifampin and it should not be used if this strain is suspected.

If not treated appropriately, brucellosis can lead to long-term disease associated with arthritis, endocarditis, chronic fatigue, depression, or swelling of the liver or spleen.

Visit the CDC’s brucellosis website or consult the CDC’s brucellosis reference guide for more information on the different types of diagnostic tests available, treatment, and prevention of brucellosis.

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