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A granulomatous-looking lesion was observed in the caudal mediastinal lymph node of a calf.

So far this year we have analyzed 23 granulomatous lesions in cattle of which 4 have been confirmed as cases of tuberculosis, remember that the annual goal is to analyze 100 granulomas.

Under the microscope, pyogranulomatous lymphadenitis with areas of necrosis, abundant neutrophilic polymorphonuclear leukocytes, and very abundant multinucleated giant cells could be observed.

Granulomatous lesion in the caudal mediastinal lymph node of a bovine.

Wide multifocal areas of necrosis (darker areas) are observed under the microscope, with mineralization and abundant pyogranulomatous inflammatory infiltrate.

In this enlarged image we can see neutrophilic polymorphonuclear leukocytes (asterisk) as well as very abundant multinucleated giant cells, some of them compatible with Langhans Cells (arrow) that are characterized by presenting the nuclei at the periphery.

In some of the multinucleated cells basophilic filamentous structures can be observed inside them (arrows).

 

What is your diagnosis? (85)

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Abundant colonies of gram-positive bacteria compatible with Nocardia spp. could be cultured. This bacterium can also cause granulomatous lesions in the lung and laboratory tests are needed to differentiate them from tuberculosis. A correct anatomopathological and microbiological laboratory diagnosis will allow to rule out the suspicion of tuberculosis. This way the farm won't loose its TB-free status and there will be no need to wait for a negative result from the mycobacteria culture, which usually takes quite a long time. The presence of neutrophilic polymorphonuclear leukocytes and the visualization of filamentous structures within the cytoplasm of giant cells was indicative of a bacterial etiology. The presence of giant cells should make us think of tuberculosis but they do not usually appear in such big amounts. Ziehl Neelsen's staining gave a negative result.

Blood agar with abundant colonies compatible with Nocardia spp.


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Question 1
Which microorganism do you think was cultured from this lesion?
A
Mycobacterium bovis
B
Corynebacterium pseudotuberculosis
C
Rhodococcus equii
D
Mycobacterium caprae
E
Nocardia spp.
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