Brucellosis is an infectious disease
Pathophysiology
1) caused by infection with one of four Brucella species – B. abortus (cattle), B. melitensis (sheep, goats, and camels), B. suis (hogs), and B. canis (dogs) 2) most severe disease occurs wtih B. Melitensis infections
Signs and Symptoms
1) generally occurs in two stages 2) first stage – either sudden onset of symptoms (intense headache, fever, chills, or malaise) or insidious onset (headache, pain in posterior neck, myalgias, and nighttime fever (often to 104-105 degrees F) followed by early morning sweats 3) first stage – lasts several weeks followed by a several day to several week remission 4) second stage – marked by fever, abdominal pain, constipation, backache, weakness, emotional lability, splenomegaly, and lymphadenopathy
Characteristic Test Findings
Laboratory – 1) positive titers > 1:160 with IgM antibodies present indicate active disease 2) WBC count is usually normal Joint aspiration – 3) WBCs are present in fluid Lumbar puncture – 4) increased pressure 5) increased cell count 6) increased protein
Histology/Gross Pathology
small aerobic, gram-negative, facultative intracellular organism
Associated Conditions
1) chronic form of brucellosis exists with protean signs and symptoms, including the following 2) heart – endocarditis (leading cause of death), pericarditis, mycotic aneurysms 3) gastrointestinal – diarrhea, abdominal pain, hepatosplenomegaly 4) respiratory – flu-like symptoms 5) genitourinary – epididymitis, prostatitis, acute pyelonephritis, dysmenorrhea 6) CNS – meningitis, encephalitis, abscesses, Guillain-Barre 7) musculoskeletal – suppurative arthritis, joint pain and arthralgias, spinal osteomyelitis 8) endocrine – adrenal insufficiency, syndrome of inappropriate antidiuretic hormone (SIADH)
Biochemistry
organisms invade and survive in host phagocytes by lysosome/phagosome inhibition
Inheritance/Epidemiology
1) wide variation in incubation period ranging from several days to several months (2 week average) 2) acquired by contact with body fluids of infected animals, including drinking infected milk (also possible to contract via inhalation 3) occupational disease of meat packers, farmers, and animal handlers 4) occurs rarely in USA and Western countries (200 cases/year in USA) 5) more prevalent in Middle East, Mexico, and Central America
Treatment
1) bedrest during acute febrile illness 2) combination antibiotic therapy with doxycycline and an aminoglycoside for 4 weeks followed by doxycycline and rifampin for four weeks 3) vaccine exists for use in endemic areas 4) organism is effectively killed by pasteurization or heating
Tips for USMLE
1) this infection can cause almost any conceivable symptom or sign 2) if the patient has drunk unpasteurized milk, think brucellosis or Listeria infection
