Brucellosis

Brucellosis is a bacterial zoonotic disease caused by infection with Brucella species, which are small, Gram-negative, nonmotile, nonspore-forming coccobacilli that function as facultative intracellular parasites. Four species are known to infect humans: B. melitensis (most virulent, primarily infecting goats), B. abortus (less virulent, primarily a disease of cattle), B. suis (intermediate virulence, chiefly infecting pigs), and B. canis (affecting dogs). The disease is also known by several historical names including undulant fever, Malta fever, and Mediterranean fever.

The clinical presentation of brucellosis typically begins with flu-like symptoms including fever, weakness, malaise, and weight loss, though the disease may manifest in many atypical forms. A characteristic triad of undulant fevers, profuse sweating often with a distinctive foul moldy odor likened to wet hay, and migratory arthralgia and myalgia is associated with the initial bacteremic phase. The disease duration is highly variable, ranging from a few weeks to many months or even years, and may become chronic. Laboratory findings commonly reveal leukopenia, anemia, and elevated liver enzymes. The incubation period is also variable, ranging from one week to two months but usually falling within two to four weeks.

Brucellosis is found globally and is a reportable disease in most countries, representing one of the most widespread zoonoses transmitted from animals to humans. The disease affects individuals of all ages and both sexes, with most cases in the general population resulting from consumption of raw milk or its derivatives, particularly fresh cheese made from sheep and goat products. Human brucellosis has serious public health consequences in endemic areas, where expansion of animal industries, urbanization, and inadequate hygienic measures in animal husbandry and food handling contribute to ongoing transmission. Wildlife reservoirs including bison, elk, wild boars, and deer have been identified as significant carriers that contribute to disease persistence and transmission, particularly in North America and Europe.

Humans acquire brucellosis through three primary routes: direct contact with infected animals, consumption of contaminated animal products, and inhalation of airborne agents. Most cases result from ingesting unpasteurized milk or cheese from infected goats or sheep. Occupational exposure represents a significant transmission pathway for individuals working with livestock, including farmers, butchers, hunters, veterinarians, and laboratory personnel who have contact with blood, placenta, fetuses, and uterine secretions. Hunters face elevated risk through direct handling of infected carcasses during field dressing and consumption of undercooked wild game meat, with transmission occurring through skin abrasions, mucous membranes, or aerosol exposure.

Brucellosis affects people of all ages and both sexes, though certain populations face substantially elevated risk due to exposure patterns. Individuals who consume raw milk or unpasteurized dairy products, particularly fresh cheese made from sheep or goat milk, represent the primary at-risk group in the general population. Occupational groups at highest risk include farmers, butchers, hunters, veterinarians, and laboratory personnel who have direct contact with infected animals or their tissues and secretions including blood, placenta, fetuses, and uterine discharges. Hunters and consumers of wild game face additional risk from handling infected carcasses and consuming undercooked meat from wildlife reservoirs such as bison, elk, wild boars, and deer.

Prevention of brucellosis is based on surveillance and control of risk factors, with the most effective strategy being elimination of infection in animal populations. In enzootic areas with high prevalence rates, vaccination of cattle, goats, and sheep is recommended, while serological testing and culling of infected animals can be effective in lower prevalence settings. Where eradication in animals is not feasible, prevention of human infection relies on raising awareness, implementing food-safety measures including pasteurization of milk for direct consumption and derivative products, enforcing occupational hygiene practices, and ensuring laboratory safety protocols. Personal protective equipment during animal handling and thorough cooking of game meat provide additional protection for high-risk groups.

Brucellosis is a reportable disease in most countries, making it subject to mandatory notification requirements that support systematic surveillance. The disease's nonspecific clinical presentation, including mild symptoms that may not prompt consideration of brucellosis, presents diagnostic challenges and may result in underreporting. Serological testing, particularly the standard agglutination test, remains the most commonly used diagnostic method in endemic areas, though definitive diagnosis requires isolation of the organism from blood, body fluids, or tissues. Coordination between public health and animal health sectors is essential for effective surveillance, with WHO supporting countries through the Global Early Warning System for Major Animal Diseases in collaboration with FAO, OIE, and the Mediterranean Zoonoses Control Programme.

1. 1 WHO Fact Sheet. Brucellosis.
2. 2 WHO Q&A. News.
3. 3 Wikidata. brucellosis.
4. 4 Wikipedia. Brucellosis - Wikipedia.

ICD-10

A23

ICD-11

1B92

Total cases

887K

Total deaths

40

Peak month

2022-06

Coverage

4 reporting countries · 2000-01-01 → 2026-05-09