Injection Site Injury in Poultry
Injection of antimicrobials and vaccines in any location can result in focal inflammatory myositis (see ). Cellulitis and myositis in the neck region, causing postural and/or neurological signs, can develop in poultry after improper administration of vaccines.
Necropsy image of a backyard chicken, showing a focus of muscle necrosis in the pectoralis major muscle.
Courtesy of Dr. A. J. Van Wettere.
Injection site injury is most common in broiler chicks. Affected birds might show ataxia, twisting of the neck, leg paralysis, and recumbency.
Swelling of the subcutis and muscle in the neck region at the injection site is evident grossly. Microscopically, lymphocytic and/or granulomatous inflammation is present within the muscle and subcutis.
Inflammatory infiltrate can extend to the epidural space. With oil-emulsion vaccines, empty spaces representing lipid droplets surrounded by a granulomatous inflammatory reaction are evident (see ).
Necropsy image of a chicken, showing pectoral muscle injury after injection of an oil-adjuvant vaccine. Note the hemorrhage and muscle necrosis.
Courtesy of Dr. D. Frame.
Minimal Myopathy in Poultry
Minimal myopathy can occur in otherwise normal meat-type poultry. Affected birds show no clinical signs, and their muscles are grossly normal; microscopically, however, mild myofiber degeneration and fat accumulation between myofibers are observed (see ). Focal or multifocal scattered myofibers are hyalinized and mineralized.
Photomicrographs of transverse (A) and longitudinal (B) sections of the pectoral muscle from a broiler chicken with minimal myopathy. (A) Note the focal area showing variation in myofiber size, swollen rounded hyalinized myofibers, and myofiber degeneration with fragmentation, with and without inflammation. H&E stain; original magnification 200X. (B) Note the myofiber degeneration and necrosis. H&E stain; original magnification 400X.
Images courtesy of Dr. H. J. Barnes.
More severe examples of minimal myopathy lesions contain individual myofiber necrosis, increased fat, and fibroplasia between fibers. No specific cause has been determined for these minimal changes, which have been observed by avian pathologists but are not well described in the literature.
"Minimal myopathy" is not an established name for this condition.
For More Information
Crespo R. Developmental, metabolic, and other noninfectious disorders. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:1286-1329.
