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Volume 32, Number 10—October 2026

Dispatch

Detection of Highly Pathogenic Avian Influenza A(H5N1) Virus in Cat and Rats during Outbreak in Backyard Poultry, United States, 2025

Suzanna M. Storms, Jade Rathmann, Lynette Hemker, Miranda Vieson, and Leyi WangComments to Author 
Author affiliation: Texas A&M Veterinary Medical Diagnostic Laboratory, College Station, Texas, USA (S.M. Storms); University of Illinois College of Veterinary Medicine, Urbana, Illinois, USA (S.M. Storms, M. Vieson, L. Wang); Greenville Veterinary Clinic, Ltd, Greenville, Illinois, USA (J. Rathmann, L. Hemker)

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Figure 3

Histopathology and immunohistochemistry of lesions in a cat and rat found dead during outbreak of highly pathogenic avian influenza A(H5N1) virus in backyard poultry, United States, 2025. A–C) Cat samples; D–F) rat samples. A) Hematoxylin and eosin (H&E) stain of feline lung tissue showing bronchointerstitial pneumonia; original magnification ×10. Inset (immunohistochemical [IHC] stain) shows positive immunoreactivity (arrow) of the cytoplasm of apical epithelial cells within distal airways. Scale bar indicates 20 μm. B) H&E stain of feline brain tissue showing nonsuppurative meningoencephalitis (arrows). Scale bar indicates 100 μm. C) IHC stain of feline brain showing strong immunoreactivity in cerebrocortical glial cells and neurons. Scale bar indicates 100 μm. D) H&E stain of rat lung tissue showing background alveolitis. Original magnification ×20. E) H&E stain of rat brain tissue showing nonsuppurative periventricular encephalitis (arrows). Scale bar indicates 50 μm. F) IHC of rat brain tissue showing influenza immunoreactivity in few periventricular neurons (arrows). Scale bar indicates 50 μm.

Figure 3. Histopathology and immunohistochemistry of lesions in a cat and rat found dead during outbreak of highly pathogenic avian influenza A(H5N1) virus in backyard poultry, United States, 2025. A–C) Cat samples; D–F) rat samples. A) Hematoxylin and eosin (H&E) stain of feline lung tissue showing bronchointerstitial pneumonia; original magnification ×10. Inset (immunohistochemical [IHC] stain) shows positive immunoreactivity (arrow) of the cytoplasm of apical epithelial cells within distal airways. Scale bar indicates 20 μm. B) H&E stain of feline brain tissue showing nonsuppurative meningoencephalitis (arrows). Scale bar indicates 100 μm. C) IHC stain of feline brain showing strong immunoreactivity in cerebrocortical glial cells and neurons. Scale bar indicates 100 μm. D) H&E stain of rat lung tissue showing background alveolitis. Original magnification ×20. E) H&E stain of rat brain tissue showing nonsuppurative periventricular encephalitis (arrows). Scale bar indicates 50 μm. F) IHC of rat brain tissue showing influenza immunoreactivity in few periventricular neurons (arrows). Scale bar indicates 50 μm.

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Page created: August 20, 2026
Page updated: September 28, 2026
Page reviewed: September 28, 2026
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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