A 4-year-old malnourished child with chronic diarrhea presents with recurrent respiratory infections, rough dry skin, and frequent diarrhea. Examination reveals Bitot spots on the conjunctiva. The increased susceptibility to infections in vitamin A deficiency is primarily due to which mechanism?

• A Impaired NAD+ synthesis from tryptophan
• B Failure of thymic lymphocyte maturation
• C Defective neutrophil oxidative burst
• D Squamous metaplasia of mucosal epithelia with loss of barrier function ✓

Explanation

Vitamin A deficiency causes squamous metaplasia of mucosal epithelial surfaces, particularly respiratory and gastrointestinal tracts. This replaces normal mucus-secreting epithelium with keratinized stratified squamous epithelium, destroying the mucociliary barrier and increasing infection risk. The child has Bitot spots (conjunctival xerosis) and phrynoderma, classic for vitamin A deficiency. This mechanism is distinct from the visual cycle role of vitamin A.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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