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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.
Epidemiology
The causative organisms of human brucellosis are Brucella
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. Brucella infections of deer, bison, horses, moose, caribou, hares, chickens, and desert rats have also occurred.
Brucellosis is acquired by direct contact with secretions and excretions of infected animals and by ingesting raw milk or milk products containing viable organisms. It 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.
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. Onset may also 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, the 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.
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.
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.
Diagnosis
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.
Treatment
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 made from unpasteurized milk that 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 shortlived, on the order of 2 yr.
Last full review/revision November 2005
Content last modified November 2005
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