Mitchell JL, MacDougall L, Dobromylskyj MJ, Smith K, Stavinohova R, Gunn-Moore DA, Hope JC, Scurrell E. Ocular mycobacterial lesions in cats.
Vet Pathol 2022;
59:792-805. [PMID:
35587045 PMCID:
PMC9358306 DOI:
10.1177/03009858221098431]
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Abstract
Ocular mycobacterial infections are an under-recognized cause of morbidity in the
domestic cat. This study aimed to explore the distribution, histopathological
appearance, and severity of feline ocular mycobacterial lesions, and to
characterize the immune cell population with immunohistochemistry. Routine
histological staining with hematoxylin and eosin, and Masson’s trichrome, was
performed to identify ocular lesions and assign an inflammation score based on
the number of cells present. Acid-fast bacilli were detected with Ziehl-Neelsen,
and immunohistochemistry for ionized calcium-binding adaptor protein-1 (Iba1),
calprotectin, cluster of differentiation 3 (CD3), and Pax5 was undertaken on
formalin-fixed paraffin-embedded tissue samples from 24 cases of ocular
mycobacteriosis. Posterior or panuveitis with concurrent retinitis was
identified in 20/24 cases (83%), with retinal detachment in 16/20 (80%) of these
cases. Choroidal lesions had the highest median inflammation score.
Ziehl-Neelsen-positive organisms were detected in 20/24 cases (83%), with the
highest prevalence of acid-fast bacilli detected in choroidal lesions (16/20,
80%). Lesions were typically granulomatous to pyogranulomatous, characterized by
abundant numbers of Iba1-positive macrophages, followed by calprotectin-positive
granulocytes and monocytes, fewer T cells, and rarer B cells. However, where
iritis was identified, inflammation was typically lymphoplasmacytic (11/16
cases, 69%). Where diagnostic testing was performed, tuberculosis (ie, infection
with Mycobacterium bovis, Mycobacterium
microti, or a nonspeciated Mycobacterium
tuberculosis-complex pathogen) was diagnosed in 20/22 cats (91%),
with Mycobacterium lepraemurium infection identified in the
other 2/22 cats (9%). These results suggest the choroid is the primary site of
lesion development in most cases of feline ocular mycobacteriosis, and
inflammatory changes are associated with the presence of mycobacteria localized
to ocular tissues.
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