Brucella

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Brucella melitensis

Brucella is a genus of Gram-negative bacteria, which are primarily known to cause brucellosis, a zoonotic infection transmitted from animals to humans. The disease is also known as Malta fever, Mediterranean fever, or undulant fever, reflecting its diverse symptoms and geographical spread. Brucella species are small, non-motile, non-spore-forming, rod-shaped (coccobacilli) bacteria that affect various animal hosts, including cattle, goats, camels, and dogs, leading to significant economic losses in the livestock industry.

Classification and Structure

The genus Brucella belongs to the family Brucellaceae. It comprises several species, with Brucella melitensis (affecting goats and sheep), Brucella abortus (affecting cattle), Brucella suis (affecting pigs), and Brucella canis (affecting dogs) being the most significant in terms of their pathogenicity to humans. These bacteria are characterized by their lack of a capsule, their aerobic nature, and their requirement of complex media for laboratory culture.

Pathogenesis and Clinical Features

Brucella spp. are facultative intracellular pathogens that can survive and multiply within phagocytes, making them adept at evading the host's immune response. The transmission to humans typically occurs through direct contact with infected animals or their secretions, or by consuming contaminated animal products, particularly unpasteurized milk and cheese.

The clinical manifestations of brucellosis in humans can range from mild to severe, including fever, sweats, malaise, anorexia, headache, muscle pain, back pain, and physical weakness. Chronic infections may lead to more serious complications such as arthritis, endocarditis, or involvement of the central nervous system.

Diagnosis and Treatment

Diagnosis of brucellosis is primarily based on serological tests, which detect antibodies against Brucella spp., and by culturing the bacteria from blood or other bodily fluids. Due to the bacteria's slow-growing nature, cultures may need to be incubated for up to six weeks before a negative result is confirmed.

Treatment typically involves a combination of antibiotics to prevent relapse and to ensure the eradication of the bacteria. The most commonly used antibiotics include doxycycline, rifampin, streptomycin, and gentamicin. Treatment duration can be lengthy, often requiring several weeks to months of therapy.

Prevention

Preventive measures against brucellosis include vaccination of animals, control and eradication programs in livestock populations, and public health measures such as pasteurization of milk and dairy products. Personal protective equipment is recommended for individuals working in high-risk occupations, such as veterinarians, farmers, and slaughterhouse workers, to prevent direct contact with infected animals or their secretions.

Economic and Public Health Impact

Brucellosis poses significant economic and public health challenges, particularly in regions where animal vaccination programs are not thoroughly implemented, and where consumption of raw dairy products is common. The disease causes considerable livestock productivity losses due to reproductive failures in infected animals. In humans, the chronic nature of the disease can lead to long-term disability, affecting an individual's quality of life and economic productivity.