Brucellosis

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What is Brucellosis?

Brucellosis is a zoonotic (animal linked) infection transmitted from animals to humans by ingestion of infected food products (such as unpasteurised milk and cheese), direct contact with an infected animal, or inhalation of aerosols. This last method of transmission is remarkably efficient given the relatively low concentration of organisms (as few as 10-100 bacteria) needed to establish infection in humans and has brought renewed attention to this old disease as a potential biological warfare agent.

Who gets Brucellosis?

In most western countries, frequency of Brucellosis infection is related to the number of infected animals. Brucellosis infected animals are considered rare, and pasteurization of milk has eliminated this method of contraction, thus Brucellosis infection generally occurs via occupational exposure (cattlemen, veterinarians, slaughterhouse workers). The incidence of brucellosis is approximately 200 per year or 0.04 per 100,000.

Frequency of brucellosis varies across nations but obviously is higher in more agrarian societies and in places where handling of animal products and dairy products is less stringent. The highest incidence of brucellosis is observed in the Middle East, Mediterranean region, China, India, Peru, and Mexico.

Mortality from brucellosis is rare and usually is secondary to the development of endocarditis.

Since exposures tend to be primarily occupational, no race, age or sex predilection exists worldwide.

Predisposing Factors

Consumption of infected meat products.

Consumption of unpastuerized cheese/milk.

Direct contact with infected animals.

Progression

The acute brucellosis incubation period is 1-3 weeks. The onset is insidious, with malaise, headache, weakness, generalized myalgia and night sweats. The fever pattern is classically undulant, although continuous and intermittent patterns are also seen. Lymphadenopathy, hepatosplenomegaly and spinal tenderness may be present; arthritis, osteomyelitis, orchitis, epididymitis, meningoencephalitis and endocarditis have all been described.

Untreated brucellosis can give rise to chronic infection, lasting a year or more. This is characterized by easy fatiguability, myalgia, and occasional bouts of fever and depression. Splenomegaly is usually present. Occasionally infection can lead to localized brucellosis. Bones and joints, spleen, endocardium, lungs, urinary tract and nervous system may be involved. Systemic symptoms of brucellosis occur in less than one-third.

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