Brucellosis is a zoonosis (zoonotic disease) spread primarily via ingestion of unpasteurized milk from infected animals. It is also known as undulant fever, Malta fever, and Mediterranean fever. The bacteria causing this disease, Brucella, are small, Gram-negative, nonmotile, nonspore-forming, rod-shaped (coccobacilli) bacteria. They function as facultative intracellular parasites, causing chronic disease, which usually persists for life. Four species infect humans: B. abortus, B. canis, B. melitensis, and B. suis. B. abortus is less virulent than B. melitensis and is primarily a disease of cattle. B. canis affects dogs. B. melitensis is the most virulent and invasive species; it usually infects goats and occasionally sheep. B. suis is of intermediate virulence and chiefly infects pigs. Symptoms include profuse sweating and joint and muscle pain. Brucellosis has been recognized in animals and humans since the early 20th century.
Signs and symptoms
The symptoms are like those associated with many other febrile diseases, but with emphasis on muscular pain and night sweats. The duration of the disease can vary from a few weeks to many months or even years. In the first stage of the disease, bacteremia occurs and leads to the classic triad of undulant fevers, sweating (often with a characteristic foul, moldy smell sometimes likened to wet hay), and migratory arthralgia and myalgia (joint and muscle pain). Blood tests characteristically reveal a low number of white blood cells and red blood cells, show some elevation of liver enzymes such as aspartate aminotransferase and alanine aminotransferase, and demonstrate positive Bengal rose and Huddleston reactions. Gastrointestinal symptoms occur in 70% of cases and include nausea, vomiting, decreased appetite, unintentional weight loss, abdominal pain, constipation, diarrhea, an enlarged liver, liver inflammation, liver abscess, and an enlarged spleen. This complex is, at least in Portugal, Israel, Palestine, Syria, Iran, and Jordan, known as Malta fever. During episodes of Malta fever, melitococcemia (presence of brucellae in the blood) can usually be demonstrated using blood culture in tryptose medium or Albini medium. If untreated, the disease can give rise to focalizations or become chronic. The focalizations of brucellosis usually occur in bones and joints, and osteomyelitis or spondylodiscitis of the lumbar spine, accompanied by sacroiliitis, is very characteristic of this disease. Orchitis is also common in men. The consequences of Brucella infection are highly variable and may include arthritis, spondylitis, thrombocytopenia, meningitis, uveitis, optic neuritis, endocarditis, and various neurological disorders collectively known as neurobrucellosis.
Cause
Brucellosis in humans is usually associated with consumption of unpasteurized milk and soft cheeses made from the milk of infected animals—often goats—infected with B. melitensis, and with occupational exposure of laboratory workers, veterinarians, and slaughterhouse workers. These infected animals may be healthy and asymptomatic. Some vaccines used in livestock, most notably B. abortus strain 19, also cause disease in humans if accidentally injected. Brucellosis induces inconstant fevers, miscarriage, sweating, weakness, anemia, headaches, depression, and muscular and bodily pain. The other strains, B. suis and B. canis, cause infection in pigs and dogs, respectively. Overall findings support that brucellosis poses an occupational risk to goat farmers with specific areas of concern including weak awareness of disease transmission to humans and lack of knowledge on specific safe farm practices such as quarantine practices.
Wildlife reservoirs and zoonotic transmission Brucellosis affects both domestic and wildlife species, with the latter serving as significant reservoirs that contribute to disease persistence and transmission. Notably, bison, elk, wild boars, and deer have been identified as carriers, particularly in North America and Europe Humans can contract the disease through direct handling of infected animals, aerosol exposure, or consumption of undercooked game meat. Additionally, the wildlife trade has been implicated in the geographical spread of brucellosis, as the movement and sale of infected animals, particularly in unregulated markets, introduce the bacteria into new ecosystems, increasing disease risks for both humans and animals. Reports from Central Asia and sub-Saharan Africa highlight cases where wildlife trafficking has facilitated brucellosis outbreaks in non-endemic regions.
Transmission through hunting and game meat consumption Hunters and individuals who consume wild game face an elevated risk of brucellosis exposure due to direct contact with infected animals and inadequate meat preparation. Transmission can occur during field-dressing or handling of infected carcasses, as Brucella bacteria can enter the body through skin abrasions, mucous membranes, or inhalation of aerosolized pathogens. Additionally, the consumption of undercooked or improperly handled wild game meat remains a significant risk factor, particularly in regions where game animals constitute a primary food source. Implementing protective measures, such as the use of personal protective equipment (PPE) during handling and ensuring thorough cooking of game meat, is essential to mitigating the risk of brucellosis transmission within hunting communities.
Diagnosis
The diagnosis of brucellosis relies on:
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