Brucellosis: Causes, Symptoms, Affected Populations, Related Disorders, Diagnosis and Treatment

It is an infectious disease that affects livestock and can be transmitted to humans.

The disorder is caused by one of the four different species of bacteria that belong to the genus Brucella.

The initial symptoms of the infection may not be specific, such as fever, muscle pain, headache, loss of appetite, profuse sweating, and physical weakness.

In some cases, the symptoms appear suddenly and are acute, while in others, the symptoms may develop over a few months.

If brucellosis is not treated in time, the disease may take months to resolve once the appropriate therapy has begun.

Brucellosis may be confined to a particular area of ​​the body (local) or have serious complications that affect various organ systems of the body, including the central nervous system.

Brucellosis can be prevented with the consumption of pasteurized cow and goat milk.


Pasteurization eliminates the bacteria that cause the disease.

However, in the case of people exposed to livestock and contact with fresh meat, they can also be affected by brucellosis.


Brucellosis is caused by the infectious bacterium Brucella.

Most cases result from exposure to infected animals or contaminated animal products.

Humans can contract the disease by eating or drinking food or liquids contaminated with Brucella, inhaling the bacteria, or direct contact through an open wound.

Most cases occur when eating contaminated food products, especially milk, cheese, or raw meat that is not pasteurized or when pasteurizing incorrectly.

Animals can carry the bacteria without presenting any symptoms, which results in the contamination of food products of animal origin, such as meat or dairy products, without the supplier’s knowledge.

Brucella is most commonly found among cattle, sheep, goats, camels, deer, elk, and pigs.

Inhalation of Brucella bacteria or direct contact through an open wound is an occupational hazard associated with slaughterhouse workers, veterinarians, farmers, and others who may contact contaminated animals.

Hunters may be at risk of developing brucellosis because they may come in contact with infected animals.

There are six known Brucella species, although only four of these species cause brucellosis in humans.

The four species of Brucella are Brucella abortus, which is transported by cattle; Brucella suis, which is fascinated by pigs; Brucella melitensis, which sheep and goats transmit; and Brucella canis, which dogs transport.

Brucella melitensis is the organism that most frequently infects humans and causes the most severe form of the disease.

Signs and symptoms

The symptoms of brucellosis vary widely among affected people.

Some people may have no apparent symptoms (asymptomatic), and others may develop serious complications that affect various organ systems.

The incubation period can vary from 1 to 3 weeks to several months.

The cases in which people experience the sudden onset of symptoms can be called acute brucellosis.

The cases in which the affected people develop the same symptoms in a few weeks can be called subacute brucellosis.

When the brucellosis infection lasts more than a year, it can be called chronic brucellosis.

Approximately 50 percent of people with brucellosis experience the sudden onset of symptoms (acute illness) for one to two days.

In some cases, symptoms develop over a few weeks (subacute disease).

The initial symptoms of brucellosis are nonspecific and resemble those of a flu-like illness.

Such symptoms may include fever, chills, generalized weakness and fatigue, headache, muscle aches ( myalgias ), loss of appetite, weight loss, night sweats, joint pain (arthralgia) and inflammation ( arthritis ), back pain, constipation, and dry cough.

In some cases, brucellosis is characterized by repeated episodes of fever intermittently for more than one year (undulant fever).

Additional symptoms in people with brucellosis include inflammation of the lymph glands (lymphadenopathy) and spleen enlargement (splenomegaly).

Enlargement of the liver ( hepatomegaly ) is a symptom that occurs less frequently.

When brucellosis affects only a specific area of ​​the body, it can be called localized brucellosis.

Localized brucellosis causes inflammation of the affected organs, including bones, skin, liver, genitourinary and gastrointestinal tract, central nervous system, and heart.

One of the most frequent sites of localized infection is the lower back, which causes inflammation and pain in the lumbar vertebrae ( osteomyelitis ).

Brucellosis can cause skin lesions in rare cases, including blemishes, ulcers, and rashes.

Abscesses can affect the liver and cause jaundice.

Infection of the genitourinary tract can cause kidney inflammation (interstitial nephritis).

In men, inflammation and pain of the testicles (epididymal-orchitis) and prostate inflammation ( prostatitis ) can also occur.

Infection of the gastrointestinal tract can cause vomiting, nausea, diarrhea, constipation, abdominal pain, and weight loss.

In some cases, brucellosis can affect the central nervous system (neurobrucellosis).

Symptoms of neurobrucellosis include inflammation of the membranes (meninges) that surround the brain and spinal cord (meningitis) and inflammation of the brain (encephalitis).

Less common symptoms may include increased pressure inside the skull (intracranial hypertension), leakage of cerebrospinal fluid into the optic disk of the eye may cause disc swelling ( papilledema ) that can result in progressive loss of vision clarity (visual acuity).

Damage to the optic nerve (optic neuropathy) potentially results in vision loss, brain bleeding (intracranial hemorrhage), and stroke.

Another potentially severe complication of brucellosis is an acute inflammation of the heart’s lining ( endocarditis ), which can occur in rare cases.

In addition, brucellosis can cause inflammation of the nerves ( neuritis ) in various body parts, visual problems, and impaired renal function.

Coagulation problems and other blood abnormalities, such as low circulating red blood cell levels, may also occur.

Affected populations

Brucellosis affects men and women in equal numbers.

The disorder is rare in the United States since pasteurization of milk is a routine, and cattle are vaccinated against this disease.

Less than 100 new cases are reported each year in the United States.

It is believed that they are introduced in this country from areas where the infection is present (endemic), or they may be related to the consumption of unpasteurized cow and goat milk.

Around the world, approximately 500,000 cases of this disease are reported to the World Health Organization (WHO) every year.

Like an infection in cattle, brucellosis occurs throughout the world, and domestic livestock is the primary source of the human condition in some parts of the world where cattle are not routinely vaccinated.

It is more common in Russia, Africa, South America, and the Middle East.

Related disorders

The symptoms of the following disorders may be similar to those of brucellosis. The comparisons can be helpful for a differential diagnosis.

Brucellosis should be differentiated from other more common causes of fever, chronic fatigue, weakness, and other nonspecific flu symptoms, especially in individuals from endemic regions.

These causes include other infectious diseases and various autoimmune diseases.


The diagnosis of brucellosis is based on a thorough clinical evaluation, a detailed history of the patient, and specific laboratory tests that can detect the presence of Brucella bacteria in the blood, bone marrow, or tissue of affected organs.

Blood cultures, bone marrow, cerebrospinal fluid (when there is meningitis), or tissue from any affected organ system can be used to identify if Brucella bacteria are present.

The body’s immune system can create antibodies against the bacteria.

Tests may be done to detect the presence of these antibodies in the body.

The most common test performed is called a serum agglutination test.

Specific X-ray tests, computed tomography, or magnetic resonance imaging can detect skeletal changes sometimes associated with brucellosis.


Antibiotics are the treatment of choice for brucellosis, usually the combination of doxycycline and streptomycin.

These medications are usually given for about six weeks.

Rifampin can be used as an alternative to streptomycin, but it is generally less effective.

Trimethoprim with sulfamethoxazole medications are an adequate alternative, but they are not as effective as doxycycline, rifampicin, or streptomycin.

There is a debate about the most effective combination therapy in the medical literature.

Suppose severe complications develop, such as acute inflammation of the membranes lining the brain (meningitis) or the heart lining ( endocarditis ). In that case, rifampin may be added to the combination of trimethoprim and sulfamethoxazole.

People with endocarditis associated with brucellosis usually require heart valve replacement in addition to antibiotic therapy.

Another treatment is symptomatic and supportive.

Less than 10 percent of people with brucellosis experience a relapse of the disease after treatment with antibiotics.

Medications with steroids such as Prednisone can be given to those affected individuals who have severe symptoms associated with the release of toxins into the blood (toxemia).

Severe pain, especially in the spine, may require pain management with soothing medications such as codeine.

People with acute brucellosis should restrict their daily activity to avoid fatigue. Absolute bed rest is recommended during periods of fever.