Brucella

Snapshot

A farmer from Argentina presents to a local clinic with daily fevers and fatigue. He supports his family by supplying wool and providing unpasteurized milk for drinking and making cheese. For the past month, he has had general malaise, daily fevers, and some nausea and vomiting. On physical exam, he has a low-grade fever but otherwise a normal physical exam. Based on his occupational exposures, he is tested for zoonotic bacterial infections and started on empiric antibiotics.

Introduction

Classification
- Brucella genus
  - most often Brucella melitensis
    - B. abortus and B. suis can also infect humans
  - facultative intracellular gram-negative zoonotic coccobacilli
  - transmission via ingestion of contaminated foods
  - causes an undulant fever
Epidemiology
- incidence
  - endemic in Mediterranean countries and South America
  - the most common bacterial zoonosis
- demographics
  - adults > children
- risk factors
  - ingestion of unpasteurized dairy products
  - occupational exposure to animals
Pathogenesis
- requires a very low dose
- the bacteria enter through the intestinal mucosa, into the lymphatics, and into the blood
- the bacteria are taken into macrophages and modify the intracellular environment to survive
Prognosis
- often recurs
if untreated, the illness may progress to chronic disease that lasts for years

Presentation

Imaging

Magnetic resonance imaging (MRI)
- indication
  - suspected neurologic involvement
- findings
abnormal enhancement in the meninges

Studies

Labs
- culture of bacteria from blood or bone marrow
- detection of immunoglobulin G (IgG) and IgM on serology
Making the diagnosis
based on clinical presentation and confirmed with laboratory studies

Differential

Treatment

Complications