Brucellosis (cont.)

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What causes brucellosis?

Brucellosis is a systemic infectious disease transmitted from certain animals to humans (zoonotic disease). Brucellosis in humans is predominantly caused by four different species of Brucella bacteria: Brucella melitensis (goats, sheep, camels), Brucella suis (pigs), Brucella abortus (cows, buffalo, elk, camels, yaks), and Brucella canis (dogs). Though all of these species can cause human brucellosis, Brucella melitensis is the most prevalent worldwide, and it is felt to cause the most severe cases of brucellosis.

How is brucellosis transmitted?

Brucellosis is transmitted from animals to humans in several ways. The most common route of transmission occurs when humans consume raw milk or cheese from infected sheep and goats. Infected animals shed the organism into their milk, and if humans eat or drink unpasteurized dairy products from these affected animals, they can develop brucellosis.

Brucellosis can also be transmitted to humans via inhalation of the organism or by direct contact with infected animal secretions. The bacteria can gain entry into the body through the inhalation of aerosolized secretions, through breaks in the skin, or through exposure of the mucous membranes/conjunctiva from the splashing of infected secretions. With these routes of entry, brucellosis is an occupational disease that can affect veterinarians, slaughterhouse workers, butchers, hunters, laboratory personnel, and those individuals who work closely with livestock (for example, farmers and shepherds).

Finally, an accidental injection with the livestock vaccine used against Brucella abortus can also lead to brucellosis in humans. Human-to-human transmission is very rare (via sexual contact and breastfeeding).

What are the symptoms and signs of brucellosis?

The symptoms and signs of brucellosis may develop from days to months after the initial exposure to the organism (incubation period). While some individuals may develop mild symptoms, others may go on to develop long-term chronic symptoms.

The signs and symptoms of brucellosis are extensive and they can be similar to many other febrile illnesses. They include

  • fever (the most common finding, and it may be intermittent and relapsing),

  • sweating,

  • body aches,

  • joint pain,

  • fatigue,

  • weakness,

  • dizziness,

  • headache,

  • depression,

  • irritability,

  • loss of appetite,

  • weight loss,

  • cough,

  • difficulty breathing,

  • chest pain,

  • abdominal pain,

  • enlarged liver and/or spleen.

Other symptoms and signs may also be present with brucellosis. Certain variables such as the severity of illness, the chronicity of illness, and the development of complications can all impact the clinical findings associated with the disease.

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