Causative Agent

Routes of Exposure

Infective Dose & Infectivity

Incubation Period

Clinical Effects

Lethality

Transmissibility

Primary Contaminations & Methods of Dissemination

Decontamination & Isolation

Laboratory testing

Therapeutic Treatment

Prophylactic Treatment

Differential Diagnosis

References

Causative Agent: Brucellosis is a systemic zoonotic disease caused by one of four Brucella species: B. melitensis,B. abortus, B. suis, and B. canis.  The organism is a small, gram-negative aerobic coccobacillus that grows within monocytes and macrophages. 

Routes of Exposure: Transmission to humans occurs through (a) direct contact of infected tissue or body fluids with broken skin or conjunctivae, (b) inhalation of infected aerosols, or (c) ingestion of raw infected meat or unpasteurized dairy products.  The primary reservoirs are goats, cattle, sheep, pigs and camels although animals such as elk, caribou, bison, deer and wild and domestic canine animals may be infected.  Specifically, cattle and goats can carry B. melitensis, cattle can carry B. abortus, pigs can serve as reservoirs for B. suis, and dogs can serve as a reservoir for B. canis.

Infective Dose & Infectivity: 10-100 organisms

Incubation Period: Often 1-2 months, range 5 days to several months. 

Clinical Effects: Brucellosis is a systemic infection characterized by an undulant fever pattern.  It typically presents as an acute non-specific febrile illness with chills, sweats, headache, fatigue, myalgias, arthralgias, and anorexia.  Approximately 15-25% of infected individuals will have cough.  A normal chest radiograph is often present.  Lymphadenopathy is present in 10-20% of patients, and 20-30% experience splenomegaly.  Complications of brucellosis infection include: sacroiliitis, arthritis, vertebral osteomyelitis, epididymo-orchitis, and rarely, endocarditis.  Routine labs are usually non-specific. In animals, abortion is the most obvious manifestation of the disease in females and epididymitis in males. The organism is shed in the milk, fetal membranes, and uterine discharges.  Thus brucellosis can be both an occupational (veterinarians, farmers) or a foodborne disease.

Lethality: Brucellosis has a very low mortality rate, less than 5% of untreated cases, with most deaths caused by endocarditis or meningitis.

Transmissibility: Person-to-person transmission of brucellosis is extremely rare.

Primary Contaminations & Methods of Dissemination: Likely methods of dissemination would either be through aerosolization or sabotage of food. 

Decontamination & Isolation:  Patients can be managed using standard precautions. Contact precautions are suggested if draining lesions are present. No airborne isolation is required.

Laboratory testing:  If brucellosis is suspected, the diagnosis is usually made through acute and convalescent serology. Brucella can be cultured from blood, bone marrow, or other tissues, but it grows slowly. Additionally, if culture is to be done, the laboratory should be notified that brucellosis is suspected because of the high risk to laboratory workers due to transmissibility of the bacteria.

Therapeutic Treatment: The recommended treatment in adults for brucellosis is doxycycline or doxycycline plus rifampin for 6 weeks. In children under 8 years of age, trimethoprim-sulfamethoxazole is substituted for doxycycline.

Prophylactic Treatment: For cases of accidental inoculation or exposure, doxycycline and rifampin have been used as post-exposure prophylaxis.  No approved human Brucella vaccine is available. 

Differential Diagnosis: Because the initial symptoms are non-specific, the differential diagnosis is broad and includes bacterial, viral and mycoplasmal infections.  Brucellosis may be indistinguishable from typhoid fever, or the typhoidal form of tularemia.

References:

• Chin J. Control of Communicable Diseases Manual, Seventeenth Edition, American Public Health Association; 2000.

• Kortepeter M, Christopher G, Cieslak T, et al. Medical Management of Biological Casualties Handbook, U.S. Army Medical Research Institute of Infectious Diseases, U.S. Department of Defense; 2001:19-22

• Hoover DL, Friedlander AM. Brucellosis. In: Zajtchuk R, Bellamy RF, eds. Medical Aspects of Chemical and Biological Warfare. Washington, DC: Office of the Surgeon General, U.S. Department of the Army; 1997: 513-521. 

For more information call (602) 364-3289