Brucellosis is caused by Brucella sp. Symptoms begin as an acute febrile illness with few or no localized signs and progress to a chronic stage with relapses of fever, weakness, sweats, and vague aches and pains. Diagnosis is by culture, usually from the blood. Optimal treatment usually requires 2 antibiotics—doxycycline or trimethoprim/sulfamethoxazole plus streptomycin or rifampin.
The causative organisms of human brucellosis are B. abortus (from cattle), B. melitensis (from sheep and goats), and B. suis (from hogs). B. canis (from dogs) has caused sporadic infections. The most common sources of infection are farm animals and raw dairy products. Deer, bison, horses, moose, caribou, hares, chickens, and desert rats may also be infected; humans can acquire the infection from these animals as well.
Brucellosis is acquired by direct contact with secretions and excretions of infected animals and by ingesting undercooked meat, raw milk, or milk products containing viable organisms. Brucellosis is rarely transmitted from person to person. Most prevalent in rural areas, brucellosis is an occupational disease of meatpackers, veterinarians, hunters, farmers, and livestock producers. Brucellosis is rare in the US, Europe, and Canada, but cases occur in the Middle East, Mediterranean regions, Mexico, and Central America.
Patients with acute, uncomplicated brucellosis usually recover in 2 to 3 wk, even without treatment. Some go on to subacute, intermittent, or chronic disease.
Complications are rare but include subacute bacterial endocarditis, meningitis, encephalitis, neuritis, orchitis, cholecystitis, hepatic suppuration, and osteomyelitis (particularly sacroiliac or vertebral).
Symptoms and Signs
The incubation period varies from 5 days to several months and averages 2 wk. Onset may be sudden, with chills and fever, severe headache, joint and low back pain, malaise, and occasionally diarrhea. Or onset may be insidious, with mild prodromal malaise, muscular pain, headache, and pain in the back of the neck, followed by a rise in evening temperature. As the disease progresses, temperature increases to 40 to 41° C, then subsides gradually to normal or near-normal with profuse sweating in the morning.
Typically, intermittent fever persists for 1 to 5 wk, followed by a 2- to 14-day remission when symptoms are greatly diminished or absent. In some patients, fever may be transient. In others, the febrile phase recurs once or repeatedly in waves (undulations) and remissions over months or years and may manifest as FUO.
After the initial febrile phase, anorexia, weight loss, abdominal and joint pain, headache, backache, weakness, irritability, insomnia, depression, and emotional instability may occur. Constipation is usually pronounced. Splenomegaly appears, and lymph nodes may be slightly or moderately enlarged. Up to 50% of patients have hepatomegaly.
Blood cultures should be obtained; growth may take > 7 days, so the laboratory should be notified of the suspicion of brucellosis.
Acute and convalescent sera should be obtained 3 wk apart. A 4-fold increase or an acute titer of 1:160 or higher is considered diagnostic, particularly if a history of exposure and characteristic clinical findings are present. The WBC count is normal or reduced with relative or absolute lymphocytosis during the acute phase.
Activity should be restricted in acute cases, with bed rest recommended during febrile episodes.
If antibiotics are given, combination therapy is preferred. Doxycycline 100 mg po bid for 3 to 6 wk plus streptomycin 1 g IM q 12 to 24 h for 14 days lowers the rate of relapses. In children < 8 yr, trimethoprim/sulfamethoxazole (TMP/SMX) and either IM streptomycin or oral rifampin for 4 to 6 wk have been used. Severe musculoskeletal pains, especially over the spine, may require analgesia.
Pasteurization of milk helps prevent brucellosis. Cheese that is made from unpasteurized milk and is aged < 3 mo may be contaminated. People handling animals or carcasses likely to be infected should wear goggles and rubber gloves and protect skin breaks from exposure. Programs to detect infection in animals, eliminate infected animals, and vaccinate young seronegative cattle and swine are required in the US and in several other countries. Immunity after human infection is short-lived, lasting about 2 yr.
Last full review/revision August 2009 by Burke A. Cunha, MD
Content last modified February 2012