1. BRUCELLOSIS

2. Overview Brucellosis, also called undulant or Malta fever, is a prolonged febrile disease involving the reticuloendothelial system and is transmitted to man from a genitourinary infection of sheep, cattle, and pigs. Brucellosis, also called undulant or Malta fever, is a prolonged febrile disease involving the reticuloendothelial system and is transmitted to man from a genitourinary infection of sheep, cattle, and pigs.

3. Etiology Brucella abortus, Brucella abortus, B melitensis, B melitensis, B suis, B suis, B canis are gram-negative coccobacilli. B canis are gram-negative coccobacilli.

4. Manifestations There are three types of brucellosis: inapparent, acute (lasting 1 month). There are three types of brucellosis: inapparent, acute (lasting 1 month). The incubation period is about 7–21 days after contact, inhalation, or ingestion of the organisms. The incubation period is about 7–21 days after contact, inhalation, or ingestion of the organisms. Symptoms include malaise, chills, daily fevers (39–40°C), weakness, headache, backache, and anorexia and weight loss. Symptoms include malaise, chills, daily fevers (39–40°C), weakness, headache, backache, and anorexia and weight loss.

5. Especially in cases of infection due to B melitensis, the fever and drenching sweats recur in late afternoon or evening. Especially in cases of infection due to B melitensis, the fever and drenching sweats recur in late afternoon or evening. Brucellosis can continue for weeks to years. Other symptoms include splenomegaly with lymphadenopathy and hepatomegaly. Brucellosis can continue for weeks to years. Other symptoms include splenomegaly with lymphadenopathy and hepatomegaly. This recurring febrile disease can be confused with other recurring febrile illnesses (e.g., malaria and relapsing fever). This recurring febrile disease can be confused with other recurring febrile illnesses (e.g., malaria and relapsing fever).

6. Epidemiology There are around 120 cases of brucellosis cases per year in the U.S., with 50–60% occurring in handlers of livestock or meat products. There are around 120 cases of brucellosis cases per year in the U.S., with 50–60% occurring in handlers of livestock or meat products. Patients range in age from 20 to 50 years; the disease is five times more common in men than in women. Patients range in age from 20 to 50 years; the disease is five times more common in men than in women.

7. Epidemiology The disease has been reported in every state in the U.S.; however, more cases occur in states that are heavily involved in the livestock industry. The disease has been reported in every state in the U.S.; however, more cases occur in states that are heavily involved in the livestock industry. Infection results from occupational exposure to infected animals (e.g., feral swine) or consumption of unpasteurized products (e.g., milk or cheese). Organisms gain entry by contact through mucous membranes or broken skin or by inhalation or ingestion. Infection results from occupational exposure to infected animals (e.g., feral swine) or consumption of unpasteurized products (e.g., milk or cheese). Organisms gain entry by contact through mucous membranes or broken skin or by inhalation or ingestion.

8. Pathogenesis The Brucella organisms penetrate the skin or mucous membranes, are engulfed by polymorphonuclear leukocytes, and then enter the lymphatics and the bloodstream. The Brucella organisms penetrate the skin or mucous membranes, are engulfed by polymorphonuclear leukocytes, and then enter the lymphatics and the bloodstream. Brucella multiplies within the polymorphonuclear leukocytes and lyses them (facultative intracellular parasite). Brucella multiplies within the polymorphonuclear leukocytes and lyses them (facultative intracellular parasite).

9. Pathogenesis Brucella can also multiply within the macrophages of the reticuloendothelial system inducing small granulomas and abscesses. Periodic release of Brucella into the blood induces recurrent chills and fever. Antigen-specific activated macrophages are able to kill Brucella with T lymphocytes. B melitensis infections are usually the most severe.

10. Pathogenesis B abortus is associated with less frequent infection and a greater proportion of subclinical cases. The virulence of B suis strains for humans varies but is generally intermediate in severity.

11. Diagnosis Brucellosis should be suspected in patients with typical manifestations and a history of exposure. Brucellosis should be suspected in patients with typical manifestations and a history of exposure. Definitive diagnosis requires isolation of Brucella from the blood or from reticuloendothelial tissue biopsies (bone marrow). Definitive diagnosis requires isolation of Brucella from the blood or from reticuloendothelial tissue biopsies (bone marrow).

12. Diagnosis The gram-negative coccobacilli require 2– 3 days of incubation at 37°C and 5–10% carbon dioxide to produce visible colonies on blood agar. The gram-negative coccobacilli require 2– 3 days of incubation at 37°C and 5–10% carbon dioxide to produce visible colonies on blood agar. A positive tube agglutinin assay using A positive tube agglutinin assay using B abortus antigen has a titer of 160–640.

13. Therapy Therapy Treatment of brucellosis includes tetracycline plus gentamicin or streptomycin for 4–6 weeks; fever may persist 2–7 days after the start of therapy. About 10% of cases relapse within 3 months of therapy. Treatment of brucellosis includes tetracycline plus gentamicin or streptomycin for 4–6 weeks; fever may persist 2–7 days after the start of therapy. About 10% of cases relapse within 3 months of therapy.

14. Prevention Infections can be prevented by minimizing occupational exposure, pasteurizing dairy products, immunizing livestock, and destroying infected stock. Infections can be prevented by minimizing occupational exposure, pasteurizing dairy products, immunizing livestock, and destroying infected stock.