Brucellosis

Brucellosis is a zoonotic bacterial infection caused by Brucella species, acquired through direct contact with infected animals or their tissues (particularly relevant to farmers, veterinarians, and abattoir workers) or through consumption of unpasteurized dairy products, the latter representing the dominant route of acquisition in many endemic regions and an important public health target for prevention.

The organism is an intracellular pathogen, surviving and replicating within host macrophages, which contributes to both its capacity to cause chronic, relapsing disease and the specific antibiotic regimens (favoring agents with good intracellular penetration) required for effective treatment.

Presentation is often non-specific, contributing to frequent diagnostic delay, and the illness can be acute or, particularly if inadequately treated, become chronic and relapsing.

• Fever, classically described as undulant (rising and falling in a wave like pattern over weeks), though this classic pattern is not always clearly seen in practice, alongside night sweats, malaise, and significant fatigue.
• Arthralgia and myalgia are common, with sacroiliitis and peripheral large joint arthritis being recognized, relatively distinctive musculoskeletal manifestations.
• Hepatosplenomegaly and lymphadenopathy are frequently found on examination.
• Focal complications, while less common than the systemic illness, are important to recognize given their specific management implications: spondylitis (particularly lumbar, causing back pain and, if missed, potential neurological complication), epididymo-orchitis, and, rarely, endocarditis (typically affecting the aortic valve, and, though uncommon, an important cause of the small proportion of brucellosis related mortality) and neurobrucellosis (meningitis or other central nervous system involvement).

• Blood culture can be diagnostic, though the organism is slow growing and the laboratory should be specifically alerted to the clinical suspicion, since standard culture protocols and durations may need extension to reliably detect it, and there is also a recognized laboratory exposure risk requiring appropriate precautions.
• Serology (standard agglutination test and related assays) is widely used and often more practically useful than culture in many settings, with a significantly elevated or rising titre supporting the diagnosis, interpreted alongside the clinical picture and local epidemiological context, given that low level titres can also reflect past exposure without current active disease in endemic populations.
• PCR based testing offers an alternative diagnostic approach where available, with good sensitivity and the advantage of a more rapid turnaround than culture.
• FBC often shows relatively non-specific findings, sometimes with mild cytopenias reflecting reticuloendothelial and marrow involvement, and inflammatory markers are frequently elevated, though neither is specific.
• Further imaging or targeted investigation is directed by the presence of any suspected focal complication, for example spinal MRI for suspected spondylitis, or echocardiography where endocarditis is a concern.

Differentials include other causes of prolonged fever with hepatosplenomegaly, including tuberculosis, typhoid fever, and visceral leishmaniasis, alongside other causes of undulant or relapsing fever patterns.

• Combination antibiotic therapy is essential, given both the intracellular nature of the organism (favoring agents with good intracellular penetration) and a well recognized high relapse rate with monotherapy.
• A commonly used regimen combines doxycycline with rifampicin, or doxycycline with an aminoglycoside (such as streptomycin or gentamicin), typically for a minimum of six weeks, given the organism's capacity for prolonged intracellular persistence and the associated relapse risk with shorter courses.
• Focal complications generally require a longer treatment duration and, in some cases (spondylitis, endocarditis), additional specific management, including surgical input for endocarditis given the generally poor response of intracardiac brucella infection to antibiotics alone.
• Prevention centers on avoiding unpasteurized dairy products in endemic areas, appropriate personal protective equipment for those with occupational animal exposure, and broader veterinary public health measures including livestock vaccination and testing programs in endemic regions.

Referral: infectious disease input for confirmed or strongly suspected cases, particularly where treatment failure, relapse, or a focal complication (spondylitis, endocarditis, neurobrucellosis) is suspected, given the specific and prolonged management these require.