It causes brucellosis, a zoonosis (an infection acquired from animals). Brucella are Gram-negative coccobacilli, non-motile, and non-capsulated. The important species are B. abortus, B. melitensis, and B. suis. Brucellosis is also called Malta fever, undulant fever, or Mediterranean fever.

People who have close contact with animals, such as farmers and veterinarians, are at higher risk. Contaminated food, especially unpasteurized dairy products, is a common source of infection.

It typically presents as PUO (pyrexia of unknown origin) with:

• Undulating fever (the temperature rises, then falls, and the cycle repeats)
• Joint pain
• Osteomyelitis
• Lymphadenopathy
• Sometimes hepatosplenomegaly

For diagnosis, samples can be collected from blood, bone marrow, urine, or lymph node biopsy. The organism is isolated faster on special media such as trypticase soy agar, serum dextrose agar, Castaneda’s medium, and BACTEC blood culture, incubated under 10% CO2.

To detect antibodies, you can use:

• ELISA
• Complement fixation tests
• Agglutination tests

The milk ring test is used to detect animal brucellosis.