|This image depicts the colonial morphology exhibited by colonies of Brucella abortus bacterial, which had been cultivated on sheep’s blood agar (SBA), for a period of 72 hours.|
Brucella species are facultative, intracellular, gram-negative coccobacilli. Nine species of Brucella are currently defined by phenotypic and antigenic differences, in addition to differential host specificity.
- Known human pathogens: B. abortus, B. melitensis, B. suis, and B. canis.
- Pathogenicity to humans of these species is not well known: B. ovis, B. neotomae, B. ceti, B. pinnipedialis, and B. microti.
Mode of Transmission
- Eating or drinking contaminated milk products is the most common route of infection for Brucella spp.
- Brucella can enter the body via skin wounds, mucous membranes, or inhalation.
- Person-to-person transmission is very rare.
- Incubation period is 2–4 weeks (range 5 days to 5 months).
- Initial presentation is nonspecific, such as fever, muscle aches, fatigue, headache, and night sweats.
- Fever may be continuous or intermittent (undulant) .
- Systemic infection may localize in liver, spleen, bone marrow, joints, heart, or reproductive organs.
- Endocarditis is a primary cause of mortality.
- Neuropsychiatric symptoms, such as depression or sleep disturbance, are rare.
- More severe symptoms are generally associated with B. melitensis or B. suis infections than with infections from other Brucella spp.