Brucella are small parasites that can cause acute and chronic disease in both animals and humans. Brucellosis is most often spread to humans by eating or drinking unsterilized milk, raw cheese (especially goat cheese), meat products from infected animals, or having close contact with their waste products. Ticks have been known to pass the infection and transmission from human to human (mother to infant, sexual transmission) is possible.

The bacteria, discovered in the 19th century, can be shed from an infected cow at or around the time of calving. Cattle can also harbor the bacteria in their reproductive tracts. Brucella can be transmitted to uninfected dogs through breeding and contact with fetuses of infected animals. Dogs can harbor the bacteria in the genitals, eyes and kidneys. Symptoms of brucellosis in dogs include abortion in female dogs and scrotal inflammation in males. Fever is uncommon.

Brucellosis can infect humans that come in contact with infected aborted tissue or semen from dogs, cattle and other animals. As in humans, the disease is treated with antibiotics, but it is difficult to cure.

Symptoms in humans include sweating, headaches, fluctuating fevers, weakness, arthritis, depression, joint pain and muscle pain. Later symptoms may include hepatitis, endocarditis, spondylitis, anaemia, leukopenia, thrombocytopenia, meningitis, uveitis, optic neuritis and neurological disorders.

Treatment can be difficult and is not always curative. Antibiotics or combinations of antibiotics are used to try to eliminate the infections.