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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)

Main Article

Figure 3

Histopathology and immunohistochemistry of lesions in a cat and rat infected with highly pathogenic avian influenza A(H5N1) virus during outbreak in backyard poultry, United States, 2025. The cat and rat were found dead on a farm in Illinois where the outbreak occurred. A–C) Cat lung (A) and brain (B, C) tissue samples showing substantial histopathology lesions likely related to HPAIV infection. A) Hematoxylin and eosin (H&E) stain of lung tissue shows bronchointerstitial pneumonia; original magnification ×10. Inset shows immunohistochemical (IHC) stain of lung demonstrates light influenza immunoreactivity in distal airway epithelium (arrow). Scale bar indicates 20 µm. B) H&E stain of brain tissue shows nonsuppurative meningoencephalitis (arrows). Scale bar indicates 100 µm. C) IHC stain of brain shows influenza immunoreactivity in cerebrocortical glial cells and neurons. Scale bar indicates 100 µm. D–F) Rat lung (D) and brain (E, F) tissue samples. D) H&E stain of rat lung tissue shows background alveolitis. Original magnification ×20. E) H&E stain of brain tissue shows nonsuppurative periventricular encephalitis (arrows). Scale bar indicates 50 µm. F) IHC of brain tissue shows influenza immunoreactivity in few periventricular neurons (arrows). Scale bar indicates 50 µm.

Figure 3. Histopathology and immunohistochemistry of lesions in a cat and rat infected with highly pathogenic avian influenza A(H5N1) virus during outbreak in backyard poultry, United States, 2025. The cat and rat were found dead on a farm in Illinois where the outbreak occurred. A–C) Cat lung (A) and brain (B, C) tissue samples showing substantial histopathology lesions likely related to HPAIV infection. A) Hematoxylin and eosin (H&E) stain of lung tissue shows bronchointerstitial pneumonia; original magnification ×10. Inset shows immunohistochemical (IHC) stain of lung demonstrates light influenza immunoreactivity in distal airway epithelium (arrow). Scale bar indicates 20 µm. B) H&E stain of brain tissue shows nonsuppurative meningoencephalitis (arrows). Scale bar indicates 100 µm. C) IHC stain of brain shows influenza immunoreactivity in cerebrocortical glial cells and neurons. Scale bar indicates 100 µm. D–F) Rat lung (D) and brain (E, F) tissue samples. D) H&E stain of rat lung tissue shows background alveolitis. Original magnification ×20. E) H&E stain of brain tissue shows nonsuppurative periventricular encephalitis (arrows). Scale bar indicates 50 µm. F) IHC of brain tissue shows influenza immunoreactivity in few periventricular neurons (arrows). Scale bar indicates 50 µm.

Main Article

Page created: August 20, 2026
Page updated: September 18, 2026
Page reviewed: September 18, 2026
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