General Goal: To know the major cause(s) of this disease, how it is transmitted, and the major manifestations of the disease.
Specific Educational Objectives: The student should be able to:
1. recite the most common causes of brucellosis (shape and gram stain?). Is this an intracellular (if so what cells does it dwell in) or extracellular pathogen?
2. describe the common means of transmission.
3. describe the major manifestations. Since this disease is called undulant fever determine what the fever is like (high/low), the periodicity of the fever (daily, every other week), and how long the fever lasts. Other diseases have similar presentations and it will help to know the information requested above.
4. describe how you treat and prevent this infection.
Reading: MEDICAL MICROBIOLOGY by P.R. Murray, K.S. Rosenthal, G.S. Kobayashi and M.A. Pfaller, 3rd Edition. pp. 271-275.
Lecture: Dr. Neal R. Chamberlain
References:
"Brucella" abortus ("gram stain";cattle)
B. melitensis (goats)
B. suis (hogs)
B. canis (dogs)
Portal: Organisms gain entry by contact (mucous membranes or broken skin), inhalation or ingestion.
Incidence is 150-200 cases/year with 50-60 percent occurring in handlers of livestock or meat products. Patients range from 20-50 years in age and are 5 times more likely to be men than women.
Distribution: in every state, but more cases occur in states that are heavily involved in the livestock industry.
Organisms are engulfed by PMNs; enter lymphatics, then blood.
Brucella multiply within the PMNs and lyse them (facultative intracellular parasite).
Brucella multiply within the macrophages of the reticuloendothelial system inducing small granulomas and abscesses.
Periodic release of Brucella into the blood induces the recurrent chills and fever typical of Brucellosis.
Antigen-specific activated macrophages are able to kill Brucella with T-cell playing a critical role.
Brucella melitensis infections are usually
the most severe. 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.
Three types:
SYMPTOMS include: malaise, chills, fever (39-40°C [102.2-104oF])- daily fevers, weakness, headache, backache, anorexia, weight loss
Especially with B. melitensis, the fever and drenching sweats recur in the late afternoon or evening.
Undulant fever can continue for weeks to years.
Splenomegaly
Lymphadenopathy and hepatomegaly are less common
B. suis infection may result in multiple
splenic and liver abscesses that calcify and are visible radiographically.
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).
Gram-negative coccobacilli requiring 2-3 days and 5-10% CO2 to produce visible colonies on blood agar.
An tube agglutinin assay using B. abortus
antigen shows titers of 160-640. A slide latex agglutination test is available
however it is not as sensitive as the tube agglutinin test.
The untreated mortality rate is 3%.
Tetracycline with or without aminoglycosides for 4-6 weeks.
Bed rest, glucose and electrolyte solutions.
Fever may persist 2-7 days after the start of therapy.
10% of cases relapse within 3 months of therapy,
although substantial humoral and cellular immunity is present.
Pasteurize dairy products.
Immunize livestock and destroy infected stock.
No vaccine is available for human use.
