Brucellosis

Brucellosis (Malta fever, undulant fever) is a zoonosis and has a world-wide distribution, although it has been virtually eliminated from cattle in the UK. The highest incidence is in the Mediterranean countries, the Middle East and the tropics; there are about 500 000 new cases diagnosed per year.

The organisms usually gain entry into the human body via the mouth; less frequently they may enter via the respiratory tract, genital tract or abraded skin. The bacilli travel in the lymphatics and infect lymph nodes. This is followed by haematogenous spread with ultimate localization in the reticuloendothelial system. Spread is usually by the ingestion of raw milk from infected cattle or goats, although occupational exposure is also common. Person-to-person transmission is rare.

Clinical features

The incubation period of acute brucellosis is 1-3 weeks. The onset is insidious, with malaise, headache, weakness, generalized myalgia and night sweats. The fever pattern is classically undulant, although continuous and intermittent patterns are also seen. Lymphadenopathy, hepatosplenomegaly and spinal tenderness sacro-iliitis (20-30%) may be present; arthritis, osteomyelitis, epididymo-orchitis (up to 40%), meningoencephalitis and endocarditis have all been described.

Untreated brucellosis can give rise to chronic infection, lasting a year or more. This is characterized by easy fatiguability, myalgia, and occasional bouts of fever and depression. Splenomegaly is usually present. Occasionally infection can lead to localized brucellosis. Bones and joints, spleen, endocardium, lungs, urinary tract and nervous system may be involved. Systemic symptoms occur in less than one-third.

Diagnosis

Blood (or bone marrow) cultures are positive during the acute phase of illness in 50% of patients (higher in B. melitensis), but prolonged culture is needed. If using automated blood culture systems (BACTEC) incubate longer than the usual 5-7 days. This is less helpful in chronic disease where serological tests are of greater value. The brucella agglutination test, which demonstrates a fourfold or greater rise in titre (> 1 in 160) over a 4-week period, is highly suggestive of brucellosis. However, non-agglutinating IgG and IgA molecules can block the agglutinating reaction (prozone phenomenon) and the test should be carried out to a high dilution to avoid this. An elevated serum IgG level is evidence of current or recent infection; a negative test excludes chronic brucellosis. In localized brucellosis antibody titres are low, and diagnosis is usually established by culturing the organisms from the involved site. PCR for detection of Brucella in blood gives a rapid diagnosis, and along with measurement of IgG or IgM antibodies by ELISA, are highly sensitive and specific.

Management and prevention

Brucellosis is treated with a combination of doxycycline 200 mg daily and rifampicin 600-900 mg daily for 6 weeks, but relapses occur. Alternatively, tetracycline can be combined with streptomycin, which is usually given for only the first 2 weeks of treatment. Prevention and control involve careful attention to hygiene when handling infected animals, vaccination with the eradication of infection in animals, and pasteurization of milk. No vaccine is available for use in humans.