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Brucellosis; Brucella bacteria; Zoonotic disease; Animal-to-human transmission; Undulant fever; Brucella melitensis; Brucella abortus; Brucella suis; Brucella canis; Brucellosis symptoms; Brucellosis diagnosis; Brucellosis treatment; Brucellosis prevention; Unpasteurized dairy products; Occupational exposure; Livestock infections; Serological testing; Blood cultures; Antibiotic therapy; Brucellosis in humans; Brucellosis in animals

Introduction

Brucellosis is a highly contagious zoonotic infection caused by bacteria of the genus Brucella. It primarily affects livestock (cattle, goats, sheep, pigs) but can also spread to humans through direct or indirect contact with infected animals or animal products [1]. Brucellosis is a global public health concern, particularly in areas with high rates of animal husbandry. Brucellosis is a highly infectious zoonotic disease caused by bacteria of the genus Brucella, which affects both animals and humans [2]. Recognized for centuries, it continues to be a significant public health concern in many parts of the world, particularly in regions where livestock farming is prevalent and food safety regulations may be inadequate. Brucellosis primarily spreads from animals to humans through direct contact with infected animals, inhalation of airborne agents, or consumption of contaminated animal products most commonly unpasteurized milk, cheese, or undercooked meat [3]. The disease is often referred to as “undulant fever” due to its characteristic pattern of rising and falling fever. While it may begin with nonspecific symptoms such as fatigue, headache, muscle pain, and fever, if left untreated, Brucellosis can lead to chronic health complications including arthritis, endocarditis, and involvement of the liver, spleen, and central nervous system [4]. The condition can mimic other febrile illnesses, which makes diagnosis challenging and often delayed. Brucellosis is caused by different species of the Brucella genus, with Brucella melitensis (from goats and sheep), Brucella abortus (from cattle), Brucella suis (from pigs), and Brucella canis (from dogs) being the most common culprits [5-6].

These bacteria are not only highly invasive but also capable of surviving and replicating within the host’s cells, complicating eradication efforts [7]. Diagnosis typically involves serological testing and bacterial cultures, while treatment relies on a combination of antibiotics such as doxycycline and rifampicin administered over several weeks to months to prevent relapses. Preventive strategies focus on both public health education and control measures within animal populations [8].

Modes of transmission

Humans can contract brucellosis through:

Consumption of contaminated animal products

Unpasteurized dairy products (milk, cheese, yogurt).

Undercooked meat from infected animals.

Handling of tissues, blood, or fluids during animal slaughter or veterinary procedures.

Farmers, butchers, and veterinarians are at higher risk.

Common in laboratory workers handling Brucella cultures.

Potential bioterrorism risk due to airborne transmission. Once Brucella enters the human body, it invades phagocytic cells (such as macrophages), allowing it to evade immune responses. The bacteria replicate within these cells and spread to the lymph nodes, liver, spleen, and bone marrow, causing systemic infection.

Clinical manifestations

Brucellosis presents with a range of nonspecific and systemic symptoms, making it challenging to diagnose. The disease may manifest in the following forms:

Occurs when the infection persists for more than a year. Symptoms include fatigue, depression, arthritis, and spondylitis.

May lead to neurobrucellosis or cardiovascular complications.

Endocarditis, which can be fatal if untreated. Reproductive Issues: In males, it can cause orchitis or epididymitis; in females, it may lead to miscarriage or stillbirth.

Diagnosis

Diagnosing brucellosis requires a combination of clinical evaluation, laboratory testing, and epidemiological history.

Blood Culture: The gold standard for diagnosing acute brucellosis. However, it requires prolonged incubation.

• Rose Bengal Test (RBT)
• Standard Agglutination Test (SAT)
• ELISA (Enzyme-Linked Immunosorbent Assay)
• PCR (Polymerase Chain Reaction)

Brucellosis requires long-term antibiotic therapy to prevent relapses. The standard treatment regimen includes:

Doxycycline (100 mg twice daily) for 6 weeks. Rifampin (600-900 mg daily) for 6 weeks. Streptomycin or gentamicin combined with doxycycline in severe cases. Trimethoprim-sulfamethoxazole (TMP-SMX) for children and pregnant women (under physician guidance). Treatment duration is prolonged to prevent recurrence, which is common with brucellosis.

Brucellosis in pregnancy and children

Pregnant women with brucellosis are at a higher risk of miscarriage, preterm birth, or stillbirth. Early diagnosis and antibiotic treatment are crucial. In children, the disease often presents with prolonged fever and fatigue, requiring pediatric-specific antibiotic regimens.

Brucellosis is endemic in regions with extensive livestock farming, including:

• Middle East
• South and Central Asia
• Mediterranean Basin
• Latin America
• Sub-Saharan Africa

According to the World Health Organization (WHO), over 500,000 new human cases are reported annually, but the actual number may be higher due to underreporting.

Conclusion

Brucellosis is a zoonotic disease with significant public health implications. Due to its nonspecific symptoms, it often goes undiagnosed or misdiagnosed, leading to chronic complications. Preventive measures, early diagnosis, and appropriate antibiotic therapy are essential to manage and control brucellosis effectively. Brucellosis remains a significant public health and veterinary concern, especially in regions with widespread animal husbandry and limited disease control measures. Identifying the causative Brucella species and understanding their transmission dynamics are critical for implementing effective surveillance, vaccination programs, and biosecurity practices. With continued research and intersectoral collaboration between human and animal health systems, the impact of brucellosis can be significantly reduced, supporting both public health and economic stability in affected communities.

References

1. Ferrari M.J, Grais RF, Bharti N, Conlan AJK, Bjornstad ON, et al. (2008) Nature 451: 679- 684

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2. Bharti N, Djibo A, Ferrari MJ, Grais RF, Tatem AJ, et al. (2010) Epidemiol Infect 138: 1308-1316.

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3. Nic Lochlainn L, Mandal S, de Sousa R, Paranthaman K, van Binnendijk R, et al. (2016) . Euro Surveill 21: 30177

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4. Lee AD, Clemmons NS, Patel M, Gastañaduy PA (2019) . J Infect Dis 219: 1616-1623.

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5. Bharti N, Tatem AJ, Ferrari MJ, Grais RF, Djibo A, et al. (2011) Science 334: 1424-1427.

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6. Glasser JW, Feng Z, Omer SB, Smith PJ, Rodewald LE (2016) Lancet Infect Dis 16: 599-605.

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7. Funk S, Knapp JK, Lebo E, Reef SE, Dabbagh AJ, et al. (2019) BMC Med 17: 180.

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8. Wesolowski A, Metcalf CJE, Eagle N, Kombich J, Grenfell BT, et al. (2015) Proc Natl Acad Sci USA 112: 11114-11119.

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