Why does an infection of Fowl Pox (cutaneous or diphtheritic) cause lesions, blind eyes, and drop in egg production of brown layers?

Fowl Pox is a slow-spreading viral disease of chickens caused by an avipoxvirus. The virus is transmitted primarily through mosquito bites or skin abrasions. It presents in two clinical forms. The cutaneous (dry) form is characterized by the formation of hyperplastic epithelial nodules on the non-feathered skin of the comb, wattles, and eyelids. These nodules rapidly grow and coalesce into thick, black scab-like lesions. If these scabs form around the eyes, they physically close the eyelids, causing temporary or permanent blindness. The diphtheritic (wet) form targets the mucous membranes of the mouth, pharynx, and trachea, causing the formation of thick, yellow, cheesy necrotic membranes (croupous lesions). These membranes physically obstruct the respiratory tract, causing severe gasping and suffocation. In both forms, the physical inability to eat or breathe, combined with viral toxemia, causes a severe drop in egg production and high culling rates. Preventing pox requires wing-web vaccination with live Fowl Pox vaccine at 10 to 12 weeks of age. Farmers can read cutaneous virology in the Poultry Encyclopedia, buy certified live Fowl Pox vaccines on Poultry Plaza, track daily egg prices on Poultry Rates, and list healthy flocks on Murghi Mandi.