Swollen head syndrome in broiler chickens in Japan: Its pathology, microbiology and biochemistry

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Abstract
Four‐to‐seven‐week‐old broilers with swollen head syndrome (SHS) from 4 different districts of Japan were examined for pathological, microbiological and biochemical findings. Periocular and mandibular subcutaneous swelling, sometimes accompanied by ocular, hepatic and cardiac lesions were observed. Histologically, diffuse fibrinopurulent inflammation with focal granulomatous lesions was characteristic of subcutaneous tissue of the head, especially periocular tissue. The air spaces of the cranial bones and middle ear showed fibrinopurulent inflammation. Upper respiratory lesions (rhinitis, sinusitis and tracheitis) were always present in chickens with SHS. The characteristic lesions of chicken colibacillosis, i.e. fibrinopurulent serositis, panophthalmitis, fibrinous thrombi in sinusoids of the liver and fibrinous exudation in the ellipsoids and lymphoid follicles of the spleen, were occasionally seen. No virological agents could be isolated. Turkey rhinotracheitis (TRT) virus gene was detected in tracheas from two flocks by reverse transcriptase polymerase chain reaction and serum antibodies against TRT virus were present. Escherichia coli and Staphylococcus aureus were isolated from subcutaneous lesions. Serum α1‐acid glyco‐protein, an acute phase protein, was present at high concentration in chickens with SHS. This study suggests that upper respiratory lesions induce E. coli invasion into subcutaneous connective tissue adjacent to the infraorbital sinus and nasal cavity, and SHS in this study may possibly be a local infection of E. coli in facial subcutaneous connective tissue.