brucellosis

brucellosis
Name	Brucellosis
Caption	Photomicrograph of Brucella spp. bacteria
Field	Infectious disease
Symptoms	Fever, sweats, malaise, anorexia, myalgia, arthralgia
Complications	Endocarditis, arthritis, spondylitis, chronic fatigue, neurological involvement
Onset	5–60 days post-exposure
Duration	Acute to chronic
Causes	Brucella bacteria (e.g., B. melitensis, B. abortus, B. suis, B. canis)
Risks	Consuming unpasteurized dairy, occupational exposure (veterinarians, slaughterhouse workers, farmers), laboratory work
Diagnosis	Blood culture, serology (e.g., Rose Bengal test, serum agglutination test), PCR
Prevention	Pasteurization, vaccination of animals, PPE use, culling infected herds
Treatment	Antibiotic combination therapy (e.g., doxycycline with rifampicin or streptomycin)
Prognosis	Good with early treatment; risk of relapse or chronic sequelae
Frequency	~500,000 new cases annually worldwide (WHO estimate)
Deaths	Low case fatality rate (<2%) untreated; mortality higher with endocarditis

brucellosis. Brucellosis is a zoonotic infectious disease caused by bacteria of the genus Brucella. Primarily transmitted from animals to humans, it is also known as Malta fever, Mediterranean fever, or undulant fever due to its characteristic fluctuating fever pattern. The disease poses significant public health and economic burdens, particularly in regions with underdeveloped veterinary control programs.

Overview

Brucellosis is one of the most common bacterial zoonoses globally, with major impacts on both human health and livestock economies. The disease has been recognized since the time of Hippocrates and was famously described among British soldiers stationed in Malta during the Crimean War by David Bruce, who later isolated the causative agent. The World Health Organization classifies it as a neglected zoonosis, while the U.S. Centers for Disease Control and Prevention categorizes Brucella as a potential bioterrorism agent (Category B agent). Its control requires coordinated efforts between human and animal health sectors, a concept embodied in the One Health approach.

Causes and transmission

The primary causative agents are several species of the gram-negative coccobacillus Brucella. The most significant for human infection are B. melitensis (from goats and sheep), B. abortus (from cattle), B. suis (from pigs), and B. canis (from dogs). Transmission to humans typically occurs through direct contact with infected animals or their secretions, ingestion of contaminated unpasteurized dairy products like cheese or milk, or inhalation of aerosolized bacteria. High-risk occupations include veterinarians, slaughterhouse workers, farmers, and microbiologists in laboratories such as the United States Army Medical Research Institute of Infectious Diseases.

Signs and symptoms

The incubation period ranges from one week to several months. Initial symptoms are often non-specific and flu-like, including fever (classically undulant), profuse night sweats, malaise, anorexia, and headache. Myalgia and arthralgia are common. If untreated, the infection can become chronic, leading to focal complications such as spondylitis (particularly of the lumbar vertebrae), arthritis (often sacroiliitis), epididymo-orchitis, hepatomegaly, splenomegaly, and neurological manifestations like meningoencephalitis. The most severe complication is infective endocarditis, which is the leading cause of mortality.

Diagnosis

Definitive diagnosis requires isolation of the bacterium via blood culture or culture from bone marrow, though growth can be slow. Serological tests are commonly used, including the Rose Bengal test for screening and the standard serum agglutination test (Wright test) for confirmation. More advanced techniques include the anti-human globulin test (Coombs test), ELISA, and molecular methods like PCR, which can be performed at reference laboratories like the Institut Pasteur. Differential diagnosis includes typhoid fever, malaria, tuberculosis, and rheumatoid arthritis.

Treatment and prevention

Treatment requires prolonged combination antibiotic therapy to prevent relapse. A common regimen is doxycycline combined with rifampicin for at least six weeks; for severe cases like spondylitis, an aminoglycoside such as streptomycin or gentamicin is added. Prevention in humans relies on controlling the disease in animal reservoirs. Key measures include pasteurization of all dairy products, vaccination of animals (e.g., the B. abortus strain 19 and RB51 vaccines in cattle), and use of PPE for high-risk workers. In many countries, control programs overseen by bodies like the World Organisation for Animal Health involve culling infected herds.

Epidemiology

Brucellosis is endemic in the Mediterranean Basin, the Middle East, Central Asia, parts of Latin America (e.g., Mexico, Peru), and Africa. High incidence rates are reported in countries like Syria, Iran, and Mongolia. In the United States, most cases are now travel-associated or linked to consumption of unpasteurized cheeses from endemic regions, though sporadic outbreaks occur, such as those traced to raw milk in states like Texas. The European Union has achieved near-elimination in livestock through strict control programs. Global annual incidence is estimated by the World Health Organization at around 500,000 cases, though underreporting is widespread.

In animals

In livestock, brucellosis primarily causes reproductive failure, including abortions, infertility, and reduced milk yield, leading to substantial economic losses. B. abortus causes Bang's disease in cattle, while B. melitensis is the main cause in goats and sheep. Wildlife reservoirs, such as bison in Yellowstone National Park and elk in the Greater Yellowstone Ecosystem, and bison National Park, and elk and National Park and National Park and elk in the Park, and elk Park, and elk and Park Park Park, and elk the Park the Park, and Park, and Park, and Park, and elk the Park, and the Park, and Park, and the Park, and elk the Park, the Park, the Park, and Park, the Park, and Park, elk the Park, and Park, and Park, and Park, and Park, and Park, and the Park, Park, Park, Park, and Park, and Park, and Park, and Park, Park, Park, Park, Park, Park, Park, and Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park, Park Park Park