Brucellosis

What is brucellosis?

Brucellosis is a bacterial infection that people usually catch from animals or from animal products such as unpasteurized milk and cheese. It is caused by bacteria that belong to a group called Brucella. These bacteria live in animals such as sheep, goats, cattle, pigs, camels, and dogs, and they can pass to humans through direct contact with infected animals or by eating or drinking contaminated products. Doctors classify brucellosis under the medical code ICD-10 A23.9, which refers to brucellosis when the exact type of Brucella bacteria has not been specified.

Brucellosis is what doctors call a zoonosis, meaning a disease that spreads from animals to people. It occurs worldwide but is more common in regions where livestock farming is widespread and where unpasteurized dairy products are part of the local diet, including parts of the Mediterranean, the Middle East, Central Asia, Africa, and Central and South America. People who work closely with animals — such as farmers, shepherds, veterinarians, slaughterhouse workers, and laboratory staff — face a higher risk. However, anyone can develop brucellosis if they consume contaminated food or drink, including travelers returning from areas where the infection is common.

Understanding what is brucellosis matters because the illness can be vague and slow to develop, and it is sometimes mistaken for other conditions such as the flu, typhoid fever, or joint diseases. With correct diagnosis and treatment, most people recover, although the illness can be prolonged and may return if treatment is not completed.

Symptoms of brucellosis

Brucellosis symptoms can appear anywhere from a few days to several months after exposure to the bacteria, most often within two to four weeks. The symptoms are often nonspecific, which means they resemble many other illnesses. This is one reason the condition can go unrecognized for weeks or months.

Common brucellosis symptoms include:

• Fever — often coming and going in waves, which is why brucellosis has historically been called “undulant fever” (undulant means wave-like)
• Sweating — often heavy night sweats, sometimes with a distinctive odor
• Chills
• Fatigue and weakness that can be profound and long-lasting
• Joint, muscle, and back pain, particularly in the large joints and the lower spine
• Headache
• Loss of appetite and weight loss
• Enlarged lymph nodes, liver, or spleen in some cases (the lymph nodes are small glands that help fight infection; the spleen is an organ in the upper left abdomen involved in immunity)

Doctors often describe brucellosis by stage. In the acute stage — roughly the first few months of illness — fever, sweating, and body aches tend to dominate. If the infection is not treated or only partially treated, it may become chronic, meaning it lasts longer, often defined as more than a year. Chronic brucellosis often causes recurring fevers, persistent fatigue, joint pain, and low mood, and it can be harder to treat.

In some people, the bacteria settle in a particular organ or tissue, causing what doctors call focal disease. Examples include infection of the bones and joints (especially the spine and the hip or sacroiliac joints), the heart valves (a serious complication called endocarditis, which means inflammation of the inner lining of the heart), the testicles in men, the nervous system (called neurobrucellosis, which can cause meningitis — inflammation of the membranes around the brain and spinal cord), and the liver. Focal disease may need longer treatment and, occasionally, surgery.

Because symptoms can be mild, intermittent, or mistaken for other conditions, some people live with brucellosis for a long time before it is identified. If you have unexplained fevers and a possible exposure — such as contact with livestock or eating unpasteurized dairy products, especially abroad — it is worth mentioning this history to your doctor.

Causes and risk factors

Brucellosis causes trace back to Brucella bacteria carried by animals. Several species of the bacteria infect humans; the most commonly recognized are those associated with sheep and goats, cattle, pigs, and dogs. The species linked to sheep and goats tends to cause the most severe human illness.

People acquire the infection in three main ways:

• Eating or drinking contaminated products — most often raw (unpasteurized) milk, soft cheeses, butter, or ice cream made from unpasteurized milk. Undercooked meat from infected animals is a less common source. Pasteurization, the process of heating milk to kill germs, destroys Brucella bacteria.
• Direct contact with infected animals — the bacteria can enter the body through cuts or scrapes in the skin or through the moist linings of the eyes, nose, and mouth. This typically happens when handling animals, assisting with animal births, or working with carcasses, blood, or animal tissues.
• Breathing in the bacteria — inhaling contaminated dust or droplets, which is a particular risk in slaughterhouses, wool-processing facilities, and microbiology laboratories where the bacteria are handled.

Person-to-person spread is very rare. Isolated cases have been reported through breastfeeding, sexual contact, blood transfusion, and organ transplantation, but in everyday life brucellosis is not considered contagious between people.

Risk factors include:

• Working as a farmer, herder, veterinarian, slaughterhouse worker, butcher, or hunter
• Working in a laboratory that handles Brucella samples
• Consuming unpasteurized dairy products, at home or while traveling
• Living in or traveling to regions where brucellosis is common in livestock
• Assisting with livestock births without protective equipment

Prevention centers on avoiding unpasteurized dairy products, cooking meat thoroughly, wearing gloves and other protective gear when handling animals or animal tissues, and vaccinating livestock where animal vaccination programs exist. There is currently no vaccine for humans.

Diagnosis

Brucellosis diagnosis begins with a careful conversation about your symptoms and possible exposures. Because the symptoms overlap with many other illnesses, your doctor will usually ask about your occupation, travel history, contact with animals, and consumption of raw milk or fresh cheese. Telling your doctor about these exposures can significantly speed up the diagnosis.

Doctors typically confirm brucellosis using laboratory tests, which may include:

• Blood culture — a sample of blood is placed in special containers to see whether Brucella bacteria grow. This is considered the most definitive proof of infection, although the bacteria grow slowly and cultures may take days to become positive, and they do not always succeed, particularly in longer-standing illness. In some cases, bone marrow culture (taking a small sample from inside a bone) is used because it may detect the bacteria more reliably.
• Serology (antibody tests) — these blood tests look for antibodies, the proteins your immune system makes to fight the infection. Common examples include agglutination tests and enzyme-based tests. Doctors often interpret the antibody level (called a titer) together with your symptoms, and sometimes repeat the test after a couple of weeks to see whether the level is rising, which suggests an active infection.
• Molecular tests (PCR) — tests that detect the genetic material of the bacteria. These are available in some laboratories and can help confirm the diagnosis more quickly.
• General blood tests — such as blood counts and liver function tests, which may show changes that support the diagnosis, although they cannot confirm it on their own.

If your doctor suspects that the infection has settled in a specific organ, imaging may be needed. This can include ultrasound of the abdomen to check the liver and spleen, X-rays or magnetic resonance imaging (MRI) of the spine and joints if there is bone or joint pain, and echocardiography (an ultrasound of the heart) if heart valve infection is suspected. If neurobrucellosis is a concern, doctors may perform a lumbar puncture, in which a small sample of the fluid surrounding the spinal cord is taken and tested.

Because the illness can mimic conditions such as typhoid, tuberculosis, autoimmune diseases, and even some cancers of the blood, doctors may run additional tests to rule these out. Brucellosis is usually managed by infectious disease specialists; at hospitals within the Acibadem group, for example, this condition falls under the Infectious Diseases Department.

Treatment options

Brucellosis treatment relies on antibiotics, and the way they are used matters a great deal. Brucella bacteria hide inside the body’s own cells, which makes them hard to reach with a single medication or a short course. For this reason, doctors treat brucellosis with a combination of antibiotics taken for several weeks — usually at least six weeks, and longer for complicated cases. Watchful waiting is not an appropriate approach for confirmed brucellosis, because untreated infection can persist, relapse, or spread to organs.

Antibiotic therapy. The most widely used regimens combine a tetracycline-class antibiotic (commonly doxycycline) with either rifampin (an antibiotic taken by mouth) or an aminoglycoside such as streptomycin or gentamicin (antibiotics given by injection). Your doctor will choose the combination based on your age, whether you are pregnant, other health conditions, and how severe or widespread the infection is. Children and pregnant women need adjusted regimens, because some of these antibiotics are not suitable for them; alternatives such as trimethoprim-sulfamethoxazole are often used in these groups. It is very important to complete the entire course exactly as prescribed. Stopping early — even if you feel better — is one of the main reasons the infection comes back. Relapse can occur in a minority of patients even after correct treatment, usually within the first few months, and it is typically treated with another course of antibiotics.

Treatment of complicated disease. When brucellosis has spread to specific organs, treatment is longer and sometimes more intensive:

• Bone and joint infection, including spondylitis (infection of the spine), often requires several months of combination antibiotics.
• Neurobrucellosis (infection of the nervous system) usually needs prolonged treatment, often with three antibiotics that can reach the brain and spinal fluid.
• Endocarditis (infection of the heart valves) is the most dangerous form. It requires long courses of combined antibiotics and, in many cases, heart surgery to repair or replace the damaged valve.
• Abscesses (pockets of pus) in the liver, spleen, or elsewhere may need drainage — a procedure to remove the pus — or, occasionally, surgical removal of severely damaged tissue.

Supportive care. Rest, adequate fluids, and simple pain and fever relievers can help you manage symptoms while the antibiotics work. Fatigue may persist for weeks after the fever resolves, so a gradual return to normal activity is often advised.

Follow-up. Because relapse is possible, your doctor may schedule follow-up visits and repeat blood tests for several months after you finish treatment. Report any return of fever, sweats, or joint pain promptly, since early retreatment is usually effective.

Living with brucellosis / outlook

For most people who receive appropriate combination antibiotics and complete the full course, the outlook is good. Fever and sweats usually improve within days to a couple of weeks of starting treatment, although tiredness and joint aches may take longer to fade. Death from brucellosis is rare with modern treatment; the most serious risk comes from untreated heart valve infection.

Some points to keep in mind while recovering:

• Be patient with fatigue. A period of low energy after the acute illness is common and does not necessarily mean the infection has returned.
• Watch for relapse. A minority of patients experience a return of symptoms, most often within six months. Relapse is usually milder than the first episode and responds to another course of antibiotics.
• Attend follow-up appointments. Blood tests over time help your doctor confirm the infection is resolving.
• Prevent reinfection. Having had brucellosis does not provide reliable lifelong protection. Continue avoiding unpasteurized dairy products and use protective equipment if you work with animals.
• Chronic symptoms. A small number of people report long-lasting tiredness, joint pain, or low mood even after successful treatment. If this happens, ongoing follow-up with your medical team can help identify whether there is persistent focal infection or another explanation.

Brucellosis is a notifiable disease in many countries, meaning doctors report cases to public health authorities. This helps identify contaminated food sources or infected herds and protects other people in the community.

Frequently asked questions

What is brucellosis in simple terms?

Brucellosis is an infection caused by Brucella bacteria that people usually catch from animals or from unpasteurized milk and dairy products. It typically causes fever that comes and goes, heavy sweating, tiredness, and joint or muscle pain. It is treated with a combination of antibiotics taken for at least six weeks.

Can brucellosis be cured completely?

In many cases, yes. Most people recover fully when they receive the correct combination of antibiotics and complete the entire course. However, the infection can relapse in a minority of patients, usually within the first few months, so follow-up visits are important. Completing every dose of the prescribed medication is the best way to reduce the chance of the illness returning.

How serious is brucellosis?

For most people, brucellosis is an unpleasant but treatable illness. It becomes serious mainly when it goes untreated for a long time or spreads to specific organs, such as the spine, the nervous system, or the heart valves. Heart valve infection is the most dangerous complication and may require surgery. Seeking medical care early and finishing treatment greatly lowers the risk of severe outcomes.

How do people catch brucellosis?

The most common routes are consuming unpasteurized milk or cheese from infected animals and having direct contact with infected livestock — for example, during farming, veterinary work, or slaughtering. The bacteria can enter through breaks in the skin, through the eyes, nose, or mouth, or by inhaling contaminated dust. Brucellosis very rarely spreads from person to person.

How long does brucellosis treatment take?

Standard brucellosis treatment lasts at least six weeks and combines two antibiotics, because shorter courses or single drugs often fail. If the infection has spread to the bones, spine, nervous system, or heart, treatment may continue for several months. Your doctor will tailor the length of treatment to your situation and monitor your progress with follow-up tests.

How long does it take to recover from brucellosis?

Fever and sweating usually settle within days to a couple of weeks of starting effective antibiotics, but fatigue and joint aches often take longer — sometimes several weeks or more. A gradual return to normal activity is common. If symptoms return after you finish treatment, contact your doctor, as this may indicate a relapse that needs another course of antibiotics.

Can I get brucellosis from pasteurized milk?

Pasteurization — heating milk to kill harmful germs — destroys Brucella bacteria, so properly pasteurized milk and products made from it are considered safe with respect to brucellosis. The risk comes from raw milk and from cheeses, butter, or ice cream made with unpasteurized milk, particularly in regions where the infection is common in livestock.

When to see a doctor

See a doctor if you develop an unexplained fever, night sweats, persistent tiredness, or joint pain — especially if you have had contact with farm animals, work in a related occupation, have consumed unpasteurized dairy products, or have recently traveled to a region where brucellosis is common. Mention these exposures directly, as they can point your doctor toward the right tests.

Seek urgent medical attention if you have any of the following red-flag warning signs, which may indicate a serious complication:

• Severe headache with a stiff neck, confusion, or sensitivity to light — possible infection of the nervous system
• Chest pain, breathlessness, palpitations, or fainting — possible heart valve involvement
• Severe or worsening back pain with fever, especially with numbness, weakness, or tingling in the legs — possible spine infection
• High fever that does not settle or keeps returning despite treatment
• Painful swelling of a testicle in men
• Yellowing of the skin or eyes, severe abdominal pain, or marked swelling of the abdomen
• New symptoms during pregnancy with a known or suspected exposure, since brucellosis in pregnancy needs prompt specialist care

If you have already been diagnosed with brucellosis and your symptoms return after finishing antibiotics, contact your medical team, as relapse is usually most treatable when it is caught early. Care for brucellosis is generally coordinated by infectious disease specialists, who can also involve orthopedic, cardiac, or neurological teams if the infection has affected other organs.