Brucellosis in Humans: 5+ Early Signs You Shouldn’t Ignore

Brucellosis is a bacterial infection that can pass from animals to people, most commonly through contact with infected animals or by consuming unpasteurized dairy products. It is caused by bacteria from the Brucella group and can affect different parts of the body, including the bones, joints, and internal organs. The first symptoms can sometimes be mild or difficult to recognize, which makes early awareness important for proper treatment. Without treatment, brucellosis may become chronic and cause complications such as arthritis, endocarditis, and ongoing fatigue.

People may develop brucellosis after handling livestock, coming into contact with infected animal materials, or consuming contaminated milk, cheese, or other dairy products. Since the early symptoms can look similar to the flu, diagnosis may sometimes be delayed. This article covers five or more early signs of brucellosis so potential infections can be recognized sooner and medical attention can be sought before serious complications develop.

What is Brucellosis in Humans?

Brucellosis is a systemic bacterial infection and is a well-known example of a zoonotic disease, meaning it can move from animals to humans. The bacteria have the ability to enter and multiply within immune cells, which helps them remain in the body and potentially cause a prolonged infection.

Understanding how serious brucellosis can become and learning about the different names historically associated with the disease can make it easier to recognize and address the infection.

The Clinical Severity of Brucellosis in Humans

Brucellosis may begin with general flu-like symptoms that do not initially appear serious. However, the infection should not be ignored. When Brucella bacteria are not completely eliminated through appropriate antibiotic treatment, they can spread from the bloodstream and settle in different organs, potentially causing chronic and localized infections.

Some of the major complications associated with brucellosis include:

Osteoarticular Destruction: This is one of the most common long-term complications of brucellosis. The infection can affect bones and joints, resulting in arthritis, inflammation of the sacroiliac joints known as sacroiliitis, or infection of the spine called spondylitis. These conditions may cause long-lasting pain and structural damage.

Ocular and Neurological Invasion: When Brucella bacteria reach the central nervous system, they can cause neurobrucellosis. This may result in inflammation of the membranes surrounding the brain, known as meningitis, or inflammation of brain tissue called encephalitis.

Cardiovascular Endocarditis: Endocarditis is among the most serious complications of brucellosis. The bacteria may infect the inner lining of the heart and its valves. Although uncommon, this complication can be life-threatening.

Genitourinary Inflammation: In men, brucellosis can affect the reproductive system and cause inflammation of the testicles, known as orchitis, or inflammation of the epididymis, called epididymitis.

Because Brucella bacteria can remain hidden inside cells, incomplete or inadequate treatment may contribute to recurring symptoms, including fatigue, joint pain, and repeated episodes of fever.

Historical Context: The Other Names for Brucellosis

Brucellosis has been known by several names throughout medical history and in different regions. Many of these names refer to its characteristic symptoms, geographical distribution, or the researchers associated with its discovery.

Undulant Fever

Undulant Fever is one of the most commonly recognized clinical names for brucellosis. It describes the characteristic pattern in which body temperature rises and falls in waves. Fever may become more noticeable later in the day and can be accompanied by chills and heavy sweating, particularly at night.

Malta Fever

The term Malta Fever is connected to a major outbreak that affected British military personnel stationed on the island of Malta during the 19th century. In 1887, British physician Sir David Bruce isolated the organism responsible for the illness from the spleen of an infected soldier. The bacterial genus Brucella was later named in recognition of his work.

Mediterranean Fever

Mediterranean Fever reflects the historical prevalence of brucellosis in countries around the Mediterranean region. In some agricultural communities, infection has been associated with consuming unpasteurized milk and soft cheeses made from the milk of infected goats and sheep.

Other Historical Variations: Older medical sources may also use names such as Gibraltar Fever, Crimean Fever, or Bang’s Disease. Bang’s Disease specifically refers to infection caused by Brucella abortus in cattle.

Early Symptoms of Brucellosis in Humans

Identifying brucellosis in its early stages can be difficult because its symptoms often resemble those of the flu or another viral infection. The bacteria trigger an inflammatory response throughout the body, producing symptoms that may not immediately point to brucellosis. Recognizing these early signs, particularly when there has been possible animal or unpasteurized dairy exposure, can help support earlier diagnosis and treatment.

The Undulant Fever: A Wave-Like Fingerprint

One of the classic symptoms of brucellosis is a recurring fever that rises and falls in a wave-like pattern. Unlike an ordinary viral illness, where fever may settle after several days, brucellosis can cause repeated temperature changes over a longer period.

The Afternoon/Evening Spike: Fever may become more pronounced during the afternoon or evening and can occur with chills, shaking, and intense shivering.
The Morning Break: The temperature may fall considerably during the early morning hours. This can be followed by heavy sweating that may soak clothing or bedding.
The Cellular Mechanism: Brucella bacteria can survive inside immune cells called macrophages. Their persistence inside these cells contributes to ongoing immune activation and repeated inflammatory responses that can produce fever.

Migratory Joint and Widespread Muscle Pain

Joint pain, known as arthralgia, and muscle pain, or myalgia, are common features of brucellosis. The discomfort may move from one area of the body to another, sometimes making the illness difficult to distinguish from other inflammatory or rheumatologic conditions.

                    [COMMON MUSCULOSKELETAL TARGETS]
                                   │
         ┌─────────────────────────┼─────────────────────────┐
         ▼                         ▼                         ▼
   [THE SACROILIAC JOINTS]       [THE AXIAL VERTEBRAE]     [PERIPHERAL JOINTS]
 • Connects pelvis to spine.   • Infection of spinal bone.• Hips, knees, and ankles.
 • Causes deep, severe lower   • Known as spondylitis.    • Localizes in fluid.
   back and buttock pain.      • Can damage spinal bone.  • Limits overall mobility.

The discomfort can develop when the infection affects joints or bone tissue. This form of localized infection is called osteoarticular brucellosis and is one of the most frequently reported focal complications of the disease.

Bone-Deep Fatigue and Exhaustion

Brucellosis-related fatigue can be much more intense than ordinary tiredness. People may experience profound exhaustion that does not improve adequately with sleep or rest. Everyday activities such as cooking, bathing, working, or completing routine tasks may become difficult.

This fatigue is associated with the body’s prolonged immune response to the infection. Persistent inflammation and the release of inflammatory substances can contribute to weakness, low energy, and a general feeling of illness. Fatigue may also continue even after some of the other symptoms begin to improve.

Persistent Headaches and Neurological Signals

Some people with brucellosis develop persistent headaches, particularly during periods of fever. Although headaches can occur with many infections, severe or ongoing head pain should be medically evaluated.

In a smaller proportion of cases, Brucella can affect the central nervous system, causing neurobrucellosis. When this happens, headaches may occur along with symptoms such as:

Neck stiffness or a rigid neck.
Increased sensitivity to bright light (photophobia).
Confusion, memory problems, or changes in vision.

Appetite Suppression and Weight Loss

As brucellosis develops, some people experience a significant reduction in appetite, medically known as anorexia. This can eventually lead to unintended weight loss.

The body’s inflammatory response can influence appetite and energy regulation. At the same time, recurring fever and prolonged illness may increase the body’s energy requirements. When reduced food intake continues for weeks, weight and muscle mass can decline, making unexplained weight loss another possible clue when evaluating persistent brucellosis symptoms.

Causes and Transmission Routes of Brucellosis

Brucellosis is a zoonotic infection, meaning that it originates in animals and can spread to humans. The disease is caused by bacteria belonging to the Brucella genus.

Different species of Brucella are associated with different animal hosts. Understanding these sources and the ways people can become exposed is important for reducing infection risk.

The Bacterial Culprits and Their Animal Hosts

Different Brucella species are adapted to particular animal reservoirs, and exposure to these animals can influence which strain a person encounters:

Brucella melitensis (Goats and Sheep): This is an important cause of human brucellosis worldwide and is strongly associated with infections acquired from goats and sheep.
Brucella abortus (Cattle): This species is primarily associated with cattle and can cause human infection, particularly among people who work closely with livestock.
Brucella suis (Pigs/Feral Hogs): This strain is associated with domestic pigs and wild or feral swine and can affect people who hunt or process these animals.
Brucella canis (Dogs): This species is associated with dogs and can occasionally infect humans, although human infections are less common than those involving livestock-associated species.

The Three Primary Transmission Pathways

People generally acquire brucellosis through exposure to infected animals or contaminated animal products rather than through routine person-to-person contact. The major routes include ingestion, direct contact, and inhalation.

Ingestion (The Most Common Global Route)

A major route of human infection is consuming unpasteurized dairy products. When infected animals produce contaminated milk, Brucella bacteria may remain present if the milk is consumed raw or used to make unpasteurized products.

Raw milk and unpasteurized soft cheeses can therefore present an infection risk, especially in regions where brucellosis remains common among livestock.

Direct Mechanical Contact

Brucella bacteria can enter the body through cuts, scratches, or other breaks in the skin and through mucous membranes such as those of the eyes and mouth.

People may be exposed while handling infected animals or animal tissues, blood, urine, reproductive materials, placentas, or fluids associated with animal births.

Inhalation of Aerosols

In some settings, Brucella bacteria can become airborne in tiny droplets or contaminated dust particles. Breathing in these aerosols can lead to infection.

This route is particularly relevant for people working in laboratories, slaughterhouses, farms, or other environments where infected animal materials may be disturbed.

High-Risk Populations: Occupational vs. Lifestyle

The risk of brucellosis increases for people who regularly come into contact with infected animals or their products.

Category 1: Occupational Exposure Groups

People in the following occupations may face increased exposure:

Veterinarians and Livestock Ranchers: Regularly working with animals can involve exposure during births, veterinary procedures, herd management, or handling animal tissues.
Slaughterhouse and Meat-Processing Workers: These workers may come into contact with blood, organs, and other animal tissues during processing.
Laboratory Personnel (Microbiologists): Laboratory workers can be exposed when handling specimens or cultures containing Brucella, particularly if appropriate containment procedures are not followed.
Hunters: People who field-dress or process wild animals, especially feral swine and other potentially infected wildlife, may be exposed without proper protective equipment.

Category 2: Lifestyle and Dietary Exposure Groups

For the general population, dietary and travel-related exposure can be important sources of infection:

Consumers of Raw Dairy: People who consume raw milk or other unpasteurized farm products may have a greater risk of exposure.
International Travelers: Travelers visiting areas where brucellosis is more common may encounter infection risks when consuming traditionally prepared unpasteurized dairy products.

Eliminating the Transmission Chain

Reducing exposure can significantly lower the risk of brucellosis:

Heat Your Dairy: Choose pasteurized milk and dairy products because proper pasteurization is designed to destroy harmful bacteria, including Brucella.
Suit Up Individually: People who work with livestock or raw animal materials should use suitable gloves, protective clothing, and eye protection.
Use Biosafety Hoods: Laboratories handling suspected Brucella specimens should follow appropriate biosafety procedures and use certified containment equipment when required.

Complications if Early Brucellosis Symptoms are Ignored

When brucellosis is not diagnosed and treated, the infection may persist and eventually affect multiple body systems. Because Brucella bacteria can survive within cells, untreated infection may become prolonged and lead to localized complications.

These complications can involve the joints, spine, heart, nervous system, reproductive organs, liver, or spleen.

The Anatomy of Chronic Brucellosis

Long-lasting brucellosis can produce a chronic pattern in which symptoms continue or repeatedly return. The condition may be associated with symptoms such as:

Unrelenting, Exhausting Fatigue: Persistent weakness and exhaustion can continue even when other symptoms have improved.
Neuropsychiatric Disturbances: Some individuals may experience changes in mood, sleep, or other neurological and psychological symptoms during prolonged illness.
Cognitive Drop-offs (“Brain Fog”): Difficulty concentrating, memory problems, and mental cloudiness may occur.
Relapsing Waves: Fever, sweating, joint pain, and other symptoms can return after periods of improvement.

Severe Focal Complications by Organ System

If the infection continues, Brucella bacteria may establish localized infections in different tissues and organs.

The Musculoskeletal System (Most Common Site)

Bones and joints are among the most frequently affected areas in focal brucellosis.

Brucellar Spondylitis: The infection can involve the vertebrae and cause inflammation and destruction of spinal bone. Severe cases may produce abscesses or pressure on nearby nerves and the spinal cord.

Sacroiliitis and Septic Arthritis: Infection can affect the sacroiliac joints and larger peripheral joints, including the hips and knees. This may cause significant pain, inflammation, and reduced mobility.

The Cardiovascular System (The Most Lethal Site)

Heart involvement is uncommon but potentially severe. Brucella endocarditis affects the inner lining of the heart and its valves and is recognized as one of the most serious complications of brucellosis.

Damage to heart valves can interfere with normal blood flow and may lead to heart failure or other serious complications if not treated.

The Central Nervous System (Neurobrucellosis)

When Brucella affects the nervous system, the resulting condition is called neurobrucellosis. It can produce a range of neurological symptoms, including:

Chronic Meningitis and Encephalitis: Inflammation involving the protective membranes or tissues of the brain can cause headaches, neck stiffness, fever, and confusion.
Cranial Nerve Palsies: Nerve involvement may contribute to symptoms such as facial weakness, double vision, or hearing problems.

The Genitourinary and Hepatosplenic Systems

Epididymo-orchitis: In men, brucellosis may spread to the reproductive system and cause painful inflammation of the testicles and epididymis. Prompt treatment is important to reduce the risk of lasting complications.

Hepatosplenomegaly: The liver and spleen can become enlarged during systemic infection. In more advanced cases, inflammation may lead to additional tissue complications within these organs.

The Critical Importance of Early Intervention

Early diagnosis and appropriate antibiotic treatment are important because they can reduce the likelihood of persistent infection and serious focal complications. Brucellosis generally requires combination antibiotic therapy for an extended period, with the exact treatment plan depending on factors such as the infection site, severity, and individual patient considerations.

When complications have already developed in areas such as the heart, spine, or nervous system, treatment may become more complicated and can sometimes require additional medical or surgical care.

How is Brucellosis Diagnosed and Prevented?

Diagnosing and preventing brucellosis involves clinical evaluation, laboratory testing, food safety, and occupational precautions. Since the early symptoms can resemble many other infections, doctors usually consider both the person’s symptoms and their history of possible exposure.

Laboratory tests can help identify antibodies, bacterial growth, or genetic material associated with Brucella.

Medical Tests Used to Diagnose Brucellosis

Several testing approaches may be used depending on the suspected stage and location of infection.

Serological Testing (Antibody Detection)

Blood tests can identify antibodies produced by the immune system in response to Brucella infection.

Rapid Screening (The Rose Bengal Test): This test can provide a relatively quick indication of antibodies against Brucella and may be used as an initial screening method.
Quantifying the Infection (Standard Agglutination Test – SAT): The SAT measures antibody levels in the blood and can help support the diagnosis when interpreted alongside symptoms and exposure history.
Advanced Tracking (ELISA): ELISA testing can identify different antibody classes, helping physicians assess possible recent or previous exposure.

Bacterial Cultures (The Gold Standard)

Another diagnostic approach is attempting to grow Brucella bacteria from a patient’s clinical specimen.

The Samples: Samples may include blood, bone marrow, cerebrospinal fluid when neurological involvement is suspected, or fluid from a localized infection.

The Laboratory Challenge: Brucella can grow slowly, and cultures may require extended incubation. Laboratory personnel also need to use appropriate safety procedures because handling the organism can create an occupational exposure risk.

Molecular Assays (PCR Testing)

Polymerase Chain Reaction (PCR) testing can detect genetic material from Brucella. Because PCR does not require the organism to grow in culture, it may provide results more quickly in some clinical settings.

PCR can be particularly useful as part of the overall diagnostic process, although results need to be interpreted together with clinical findings and other laboratory tests.

Definitive Strategies to Prevent Infection

Since routine human-to-human transmission is uncommon, prevention mainly focuses on reducing exposure to infected animals and contaminated animal products.

The General Public: Food Safety Protocols

For most people, food safety is an important part of preventing brucellosis.

Insist on Commercial Pasteurization: Avoid unpasteurized milk and dairy products. Choosing pasteurized products greatly reduces the risk of exposure to Brucella.
Exercise Travel Vigilance: When visiting areas where brucellosis is more common, check that dairy products, including traditional cheeses, are made with pasteurized milk.

High-Risk Professions: Occupational Hazard Control

People who work with animals, animal tissues, or laboratory specimens need additional precautions.

Deploy Target PPE: Wear appropriate gloves, protective clothing, and eye protection when handling animals, animal carcasses, placentas, or birth materials.
Seal Broken Skin Barriers: Cover cuts, scratches, and other skin breaks with waterproof dressings before working around potentially infected animals or materials.
Prioritize Hand Hygiene: Wash hands thoroughly with soap and water after handling livestock, animal products, raw meat, or potentially contaminated equipment.

Conclusion

Brucellosis in humans can begin with mild, flu-like symptoms but may develop into a serious and persistent infection when left untreated. Early warning signs can include recurring fever, night sweats, joint and muscle pain, fatigue, headaches, appetite loss, and unintended weight loss. Recognizing these symptoms, especially after possible contact with infected animals or unpasteurized dairy products, can help support timely medical evaluation.

Treatment with appropriate antibiotics can help clear the infection and reduce the risk of complications involving the bones, joints, heart, nervous system, and other organs. Prevention also plays an important role. Avoiding unpasteurized dairy, following proper food-safety practices, using protective equipment around animals, and maintaining good hygiene can all reduce exposure.

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FAQ

What is brucellosis and how do humans get it?

Brucellosis is a bacterial infection caused by species of Brucella that can spread from animals to humans. People may become infected through direct contact with infected livestock or contaminated animal materials, as well as by consuming unpasteurized milk or dairy products. The infection can affect several body systems and may cause symptoms such as fever, fatigue, sweating, and joint pain. Early diagnosis and treatment can help prevent more serious complications.

What are the early signs of brucellosis?

Early symptoms may look similar to the flu and can include fever, night sweats, fatigue, muscle aches, joint pain, headaches, and a general feeling of illness. Some people may also experience reduced appetite and unintended weight loss. Symptoms can develop gradually or come and go, so a history of animal exposure or consumption of unpasteurized dairy can be an important part of the medical evaluation.

How is brucellosis diagnosed?

Doctors diagnose brucellosis by considering symptoms, exposure history, physical examination, and laboratory testing. Blood tests can look for antibodies, while cultures may be used to identify the bacteria. PCR and other laboratory methods can also help detect Brucella. Since the early symptoms are not specific to brucellosis, identifying a person’s exposure risk can be especially important.

How is brucellosis treated?

Treatment usually involves a combination of antibiotics taken for several weeks. The exact medicines and duration depend on the patient’s age, health, infection site, and severity of illness. Completing the prescribed treatment is important because inadequate treatment can increase the risk of persistent or recurrent infection. Supportive care may also be used to manage symptoms such as fever, fatigue, and joint discomfort.

Can brucellosis be prevented?

Yes. Prevention includes avoiding unpasteurized milk and dairy products, maintaining good hand hygiene, and using appropriate protective clothing when handling livestock or animal tissues. People working in veterinary, agricultural, slaughterhouse, or laboratory settings should follow occupational safety procedures. Awareness of possible exposure can also help people seek medical evaluation sooner if symptoms develop.

Who is most at risk of brucellosis?

People with frequent contact with livestock or animal products have a higher risk. This includes farmers, veterinarians, slaughterhouse workers, laboratory personnel handling Brucella, hunters, and others who work with potentially infected animals. People who consume unpasteurized milk or cheese can also be exposed. Goats, sheep, cattle, and pigs are among the animal hosts associated with human brucellosis.