• Etiology of Walking Dandruff: Cheyletiella spp. (e.g., Cheyletiella yasguri in dogs, C. blakei in cats, C. parasitovorax in rabbits) cause cheyletiellosis, colloquially called walking dandruff.
• Clinical Presentation: These are large ($400\text{--}500\ \mu\text{m}$), non-burrowing, surface-dwelling predatory-like mites possessing distinctive hook-like palpal claws. As they crawl actively across keratinaceous debris and exfoliated skin scales on the host's dorsal midline, the flaking dander visibly 'walks'.
• Differential Comparative Mites:
• Demodex: Microscopic cigar-shaped follicular mites dwelling in hair follicles and sebaceous glands.
• Notoedres: Burrowing mange mite of felids causing head mange.
• Cnemidocoptes: Burrowing mite of birds causing scaly leg and scaly face.

Correct option: (3) Cheyletiella

• Diagnostic Antigen: Pso o 2 (Psoroptes ovis allergen 2) is a major immunodominant 14.5-kDa recombinant antigen identified and cloned from the sheep scab mite, Psoroptes ovis.
• Clinical Application: Pso o 2 shares substantial structural homology with group 2 allergens from human house dust mites (Dermatophagoides pteronyssinus, Der p 2). It forms the basis of the highly sensitive and specific diagnostic Pso o 2-ELISA, allowing detection of sheep scab antibodies within 1–2 weeks post-infestation before widespread clinical crusted skin lesions appear.
• Differential Mites: Sarcoptes scabiei utilizes Sarcoptes-specific antigens (e.g., Ssag 1, Ssag 2); Psoroptes cuniculi is the ear canker mite of rabbits with related but distinct antigenic profiles.

Correct option: (3) Psoroptes ovis