PORCINE NECROTIC EAR SYNDROME
Abstract
These studies were conducted to investigate the relationship of Staphylococcus hyicus to the necrotic ear syndrome, to study the pathogenesis of the disease and to attempt to experimentally reproduce the lesions using trauma followed by the inoculation of porcine isolates of S. hyicus and (beta)-hemolytic streptococci. Sows and piglets were frequent carriers of S. hyicus but the incidence of carrier animals was lower in a herd affected with necrotic ear syndrome than in a control herd. There was no increase in the incidence of isolates from pigs 12 days after weaning when the lesions of necrotic ear syndrome first developed, nor was there any correlation between the carrier status for S. hyicus and the likelihood of developing lesions. The lesions, covered by thin scabs or thick brown crusts, developed nonrandomly as localized dermatitis at areas of trauma due to biting at the base or tip of the ear. S. hyicus along with large numbers of (beta)-hemolytic streptococci were consistently recovered from the lesions in pigs from five different swine herds. Fifty percent of the lesions healed and the balance progressed to severe necrotic ulcers. Deep ulceration developed secondarily to local cellulitis, vasculitis, thrombosis and ischemia of the auricular tissue. Initiation of the lesions depended on biting to damage the skin, but the progression to deep ulcers depended not on cannibalism but probably on local bacterial infection of the site. Histologic examination revealed numerous bacteria over the surface of ulcers, and streptococci deep in subcuticular abscesses. A localized encrusted lesion, similar to the early crusted lesions of necrotic ear syndrome produced by the inoculation of S. hyicus - Sompolinsky and (beta)-hemolytic streptococci onto a local area of trauma, did not become deeply ulcerated and necrotic. Efforts to manipulate this experimental model were hindered by the frequent development of generalized exudative epidermitis after inoculation with S. hyicus - Sompolinsky.
Degree
Ph.D.
Subject Area
Veterinary services
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