Injection of antibiotics and vaccines in any location can result in focal inflammatory myositis. Cellulitis and myositis in the neck region, causing postural and/or neurologic signs, can be seen in poultry after improper administration of vaccines. It is most commonly seen in broiler chicks. Affected birds may show ataxia, twisting of the neck, leg paralysis, and recumbency. Swelling of the subcutaneous and muscle tissue in the neck region at the injection site is seen grossly. Microscopically, lymphocytic and/or granulomatous inflammation is present within the muscle and subcutis. The inflammatory infiltrate can extend to the epidural spaces. With oil-emulsion vaccines, empty spaces representing lipid droplets surrounded by a granulomatous inflammatory reaction can be seen.
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