Zoonoses Lab: Answer Key
Case 1: Brucellosis
What is the differential diagnosis of this syndrome?
This is a presentation of a subacute, undifferentiated, systemic febrile syndrome.
The epidemiology history is essential to addressing the differential diagnosis. The
differential diagnosis on the basis of symptoms alone is very broad, and would
include tuberculosis, brucellosis, malaria, endemic mycosis (coccidioidomycosis,
histoplasmosis), cancer (generally hematologic malignancies) and a fairly long list of
other possibilities. In this case, blood cultures yielded small, aerobic but CO2-loving,
Gram-negative coccobacilli at day 8, finally identified as Brucella abortus by
biochemical and molecular methods.
What tests should be ordered immediately to rule out the most serious infections?
Malaria smears, blood cultures, chest xray, consider bone marrow biopsy
What other sites besides blood could be considered for culture?
Malaria smears were negative. Bone marrow biopsy and aspirate showed erythroid and
myeloid hyperplasia and poorly formed granulomas. No organisms were seen. Blood and
bone marrow cultures were positive on day 5 for a small gram negative coccobacillus.
What genus and species of bacteria do you think were cultivated from this patient’s
blood and bone marrow? What other species of this genus cause human zoonoses?
Brucella abortus from her probable exposure to unpasteurized cheese. Other modes
of transmission include direct exposure to animal products of parturition, abortions,
meat processing plants (occupational). Also laboratory accidents. Both modes of
transmission can be prevented by animal vaccination.
The other species include B. melitensis, usually from goats or sheep. Also, B. suis
(pigs) and, rarely, B. canis (rough, no LPS) from dogs. Syndromes include systemic
and focal, localizing disease (hepatitis, endocarditis, orchitis, spondylitis).
Why is this organism considered capable of being transformed into a bioterrorism
Brucellae are resistant to drying and can be easily aerosolized. As few as 10 inhaled
organisms can cause disease
4. Why should you tell the clinical microbiology laboratory that Brucella might be
present in the patient’s body fluids?