Brucellosis/Undulant Fever (Brucella species)
Overview
Plain-Language Overview
Brucellosis/Undulant Fever is an infection caused by bacteria called Brucella species that mainly affects the immune system and various organs. It is often transmitted to humans through contact with infected animals or consuming unpasteurized dairy products. The infection causes recurrent fevers, sweating, and muscle pain, which can come and go over weeks to months. It primarily affects the reticuloendothelial system, including the liver, spleen, and lymph nodes, leading to symptoms like fatigue and joint pain. This disease can cause long-lasting health problems if not properly diagnosed and treated.
Clinical Definition
Brucellosis/Undulant Fever is a systemic zoonotic infection caused by facultative intracellular gram-negative coccobacilli of the genus Brucella. The bacteria invade and survive within macrophages, leading to chronic granulomatous inflammation primarily involving the reticuloendothelial system. Transmission occurs through direct contact with infected animals or ingestion of contaminated animal products, especially unpasteurized milk. The disease is characterized by intermittent fever spikes (undulant fever), night sweats, arthralgia, and hepatosplenomegaly. It can cause complications such as osteomyelitis, endocarditis, and chronic fatigue. Diagnosis and management are critical due to its potential for chronicity and systemic involvement.
Inciting Event
Ingestion of unpasteurized milk or cheese contaminated with Brucella species initiates infection.
Direct contact with infected animal tissues or fluids through skin abrasions or mucous membranes triggers disease.
Inhalation of aerosolized bacteria in laboratory or slaughterhouse settings can cause infection.
Handling of aborted animal fetuses or placentas is a common source of bacterial entry.
Consumption of undercooked meat from infected animals may also serve as an inciting event.
Latency Period
Incubation period ranges from 1 to 4 weeks after exposure before symptom onset.
Symptoms may appear as early as 5 days or as late as several months post-infection.
Chronic brucellosis can develop months to years after initial exposure due to bacterial persistence.
Relapsing fever episodes may occur weeks after initial symptom resolution.
Latency varies depending on bacterial load and host immune response.
Diagnostic Delay
Nonspecific symptoms such as fever, malaise, and arthralgia often mimic other febrile illnesses causing delay.
Low clinical suspicion in non-endemic areas leads to missed or late diagnosis.
Slow growth of Brucella in blood cultures delays microbiological confirmation.
Serologic tests may be negative early in disease, requiring repeat testing.
Overlap with other infections like tuberculosis or typhoid fever complicates diagnosis.
Clinical Presentation
Signs & Symptoms
Undulating fever with intermittent spikes is the hallmark symptom of brucellosis.
Night sweats and fatigue are frequently reported systemic symptoms.
Arthralgia and myalgia commonly affect large joints and muscles.
Weight loss and anorexia occur due to chronic infection.
Headache and malaise are nonspecific but common complaints.
History of Present Illness
Intermittent undulating fever with drenching night sweats is a hallmark symptom.
Fatigue, malaise, and weight loss develop gradually over weeks to months.
Arthralgia and myalgia commonly affect large joints and the lower back.
Headache and hepatosplenomegaly may be present in systemic involvement.
Symptoms often relapse after initial improvement without treatment.
Past Medical History
Previous exposure to livestock or unpasteurized dairy products increases suspicion for brucellosis.
History of travel to or residence in endemic areas is relevant for risk assessment.
Prior episodes of febrile illness with incomplete resolution may indicate chronic infection.
Immunosuppressive conditions or therapies can worsen disease severity and prolong course.
No specific genetic predisposition is typically noted in past medical history.
Family History
There is no known hereditary pattern or familial syndrome associated with brucellosis.
Family members may share exposure risk if living in the same endemic environment or consuming the same contaminated products.
Clusters of cases in families often reflect common environmental or occupational exposures rather than genetic factors.
No genetic mutations or inherited susceptibilities have been identified for Brucella infection.
Family history is generally not contributory to diagnosis or prognosis.
Physical Exam Findings
Hepatosplenomegaly is a common finding due to reticuloendothelial system involvement.
Lymphadenopathy may be present reflecting systemic infection.
Fever is often observed during examination, typically with an undulating pattern.
Arthritis or arthralgia may be noted in affected joints, especially large joints.
Endocarditis signs such as new heart murmurs can occur in severe cases.
Diagnostic Workup
Diagnostic Criteria
Diagnosis is established by isolating Brucella species from blood, bone marrow, or other tissues using culture techniques, which is the gold standard. Serologic testing with the standard agglutination test (SAT) demonstrating high antibody titers supports the diagnosis. Clinical presentation with undulant fever, exposure history to risk factors, and compatible laboratory findings are essential. PCR assays may be used for rapid detection but are less widely available. Imaging may assist in identifying focal complications such as osteoarticular involvement.
Pathophysiology
Key Mechanisms
Intracellular survival of Brucella species within macrophages allows evasion of host immune response.
Granulomatous inflammation develops in reticuloendothelial organs causing tissue damage and systemic symptoms.
Endotoxin-mediated cytokine release triggers fever and malaise characteristic of undulant fever.
Chronic infection results from the bacteria's ability to persist in phagocytic cells leading to relapsing symptoms.
Hematogenous dissemination spreads infection to multiple organ systems including bones and joints.
| Involvement | Details |
|---|---|
| Organs | Liver is frequently affected, often showing granulomatous hepatitis in chronic brucellosis. |
Spleen enlargement occurs due to immune activation and bacterial persistence within the reticuloendothelial system. | |
| Tissues | Reticuloendothelial tissue including lymph nodes and spleen is commonly involved due to Brucella intracellular localization. |
Bone marrow involvement can lead to hematologic abnormalities and is a site of chronic infection. | |
| Cells | Macrophages are the primary host cells where Brucella species survive intracellularly, evading immune clearance. |
T lymphocytes mediate the cell-mediated immune response essential for controlling chronic brucellosis. | |
| Chemical Mediators | Interferon-gamma is critical for activating macrophages to kill intracellular Brucella organisms. |
Tumor necrosis factor-alpha contributes to granuloma formation and systemic inflammatory symptoms in brucellosis. |
Treatments
Pharmacological Treatments
Doxycycline
- Mechanism:
Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
- Side effects:
Photosensitivity
Gastrointestinal upset
Tooth discoloration in children
- Clinical role:
First-line
Rifampin
- Mechanism:
Inhibits bacterial DNA-dependent RNA polymerase, blocking RNA synthesis.
- Side effects:
Hepatotoxicity
Orange discoloration of body fluids
Drug interactions
- Clinical role:
First-line
Streptomycin
- Mechanism:
Binds to the 30S ribosomal subunit causing misreading of mRNA and inhibiting protein synthesis.
- Side effects:
Ototoxicity
Nephrotoxicity
Injection site pain
- Clinical role:
Second-line
Non-pharmacological Treatments
Avoid unpasteurized dairy products to prevent infection with Brucella species.
Supportive care including hydration and antipyretics to manage fever and systemic symptoms.
Prevention
Pharmacological Prevention
No widely recommended antibiotic prophylaxis exists for brucellosis in endemic areas.
Post-exposure prophylaxis with doxycycline and rifampin may be considered in high-risk laboratory exposures.
Non-pharmacological Prevention
Avoiding unpasteurized dairy products is the most effective prevention method.
Use of protective equipment when handling potentially infected animals or tissues.
Animal vaccination programs reduce transmission from livestock to humans.
Public health education on safe farming and food handling practices.
Screening and culling infected livestock to control outbreaks.
Outcome & Complications
Complications
Brucella endocarditis is the leading cause of mortality in brucellosis.
Osteomyelitis and spondylitis can cause chronic bone destruction.
Neurobrucellosis may lead to meningitis, encephalitis, or cranial nerve palsies.
Chronic arthritis can result in joint deformities and disability.
Abscess formation in liver, spleen, or other organs may occur.
| Short-term Sequelae | Long-term Sequelae |
|---|---|
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Differential Diagnoses
Brucellosis/Undulant Fever (Brucella species) versus Tuberculosis
Brucellosis/Undulant Fever (Brucella species) | Tuberculosis |
|---|---|
Exposure to livestock or consumption of unpasteurized dairy products | Exposure to individuals with active pulmonary tuberculosis or living in endemic areas |
Undulating fever with systemic symptoms and non-caseating granulomas | Chronic progressive illness with pulmonary involvement and caseating granulomas |
Positive blood or bone marrow culture for Brucella species | Positive acid-fast bacilli stain and culture for Mycobacterium tuberculosis |
Brucellosis/Undulant Fever (Brucella species) versus Typhoid Fever
Brucellosis/Undulant Fever (Brucella species) | Typhoid Fever |
|---|---|
Contact with infected animals or animal products | Ingestion of contaminated food or water in endemic areas |
Intermittent undulating fever with arthralgia and hepatosplenomegaly | Stepwise fever progression with relative bradycardia and abdominal symptoms |
Positive serology (standard agglutination test) or culture for Brucella | Positive blood culture for Salmonella typhi |
Brucellosis/Undulant Fever (Brucella species) versus Infective Endocarditis
Brucellosis/Undulant Fever (Brucella species) | Infective Endocarditis |
|---|---|
Occupational exposure to farm animals or ingestion of unpasteurized dairy | History of intravenous drug use or preexisting valvular heart disease |
Intermittent fever with systemic symptoms and osteoarticular involvement | Persistent fever with new or changing heart murmur and embolic phenomena |
Positive blood cultures for Brucella and absence of vegetations on echocardiogram | Positive blood cultures for typical endocarditis pathogens and echocardiographic vegetations |
Brucellosis/Undulant Fever (Brucella species) versus Q Fever
Brucellosis/Undulant Fever (Brucella species) | Q Fever |
|---|---|
Direct contact with infected livestock or consumption of unpasteurized dairy | Exposure to aerosols from parturient animals, especially sheep and goats |
Chronic undulating fever with osteoarticular and systemic symptoms | Acute febrile illness often with pneumonia or hepatitis |
Positive serology or culture for Brucella species | Positive serology for Coxiella burnetii phase I and II antibodies |
Brucellosis/Undulant Fever (Brucella species) versus Leptospirosis
Brucellosis/Undulant Fever (Brucella species) | Leptospirosis |
|---|---|
Exposure to farm animals or ingestion of unpasteurized dairy products | Exposure to water contaminated with animal urine, especially rodents |
Undulating fever with arthralgia and hepatosplenomegaly | Biphasic illness with abrupt fever, myalgia, conjunctival suffusion, and possible jaundice |
Positive serology or culture for Brucella species | Positive microscopic agglutination test for Leptospira |