African gray parrot with a nodule under the beak; fine-needle aspirate shows cornified epithelial cells. Which disease or agent is most likely?

• A. Avian pox
• B. Papillomavirus
• C. Herpesvirus
• D. Paramyxovirus

Answer: (B)

Beak-region nodules in parrots that yield keratinized, or cornified, squamous epithelial cells on fine-needle aspiration point toward a papillomavirus infection. Papillomaviruses drive proliferation of keratinocytes and hyperkeratosis, producing warty, keratin-rich growths (papillomas) on the beak and oral mucosa. The cytology of such lesions often shows cornified epithelial cells reflecting this keratinized epithelium.

Avian pox would more typically show lesions with ballooning degenerating cells and eosinophilic cytoplasmic inclusions, not mainly cornified keratinocytes. Herpesvirus tends to produce intranuclear inclusion bodies in infected epithelial cells, and paramyxoviruses usually cause different mucosal or systemic signs rather than a strictly keratinized beak nodule. Therefore, papillomavirus best explains a cornified epithelial cytology in this beak lesion.