Abstract

A unique syndrome of unilateral pectoral muscle infarction associated with fungal arteritis of the great vessels or their branches has been recognized in birds at the Zoological Society of San Diego. Of the nine cases currently identified, all were passerine species. Reported clinical signs included unilateral wing droop (n=6), inability to fly (1), and unilateral pectoral muscle swelling (1). One of the birds was simply found dead. One bird, after developing a unilateral wing droop, progressively developed pelvic limb paresis.

At necropsy, the affected muscle tissue was pale tan compared to the contralateral pectoral muscle. In six cases, the entire pectoral muscle was affected. The three remaining cases involved at least one-half of the pectoral muscle. Fungal infiltration of a major vessel was suspected on gross examination in six cases. Findings included tan masses surrounding the great vessels at the base of the heart (2), extreme thickening of the brachiocephalic trunk (1), thickening and occlusion of the left pulmonary artery (1), thickening and thrombosis of the right axillary artery and thrombosis of the proximal aorta (1). Acute coagulation necrosis of muscle fibers was found in the affected pectoral muscle in all cases. The amount of accompanying inflammation varied and likely reflected the age of the muscle infarct. Histologic examination confirmed fungal arteritis in the six cases wherein it was suspected grossly. Fungal arteritis was detected in the three remaining cases and involved the brachiocephalic trunk (1), pulmonary artery (1), and a deep pectoral artery (1). In all cases, morphology of the fungus on H&E sections was typical of Aspergillus species.¹ Aspergillus fumigatus was cultured from one case; fungal cultures were not submitted from seven birds. In one case, there was no fungal growth from the sample. Additional significant findings included respiratory aspergillosis (3), cerebral infarcts associated with fungal vasculitis (2), and hepatitis associated with fungal vasculitis (1).

In addition to the nine cases discussed above, eight additional cases of unilateral pectoral muscle infarction were also identified. Six cases were in passerine species; one case each was in a galliform species and in a columbiform species. Histologic examination of the affected pectoral muscle revealed similar findings. Respiratory infections consistent with Aspergillus sp. were found in seven of these cases. In the remaining case, pectoral muscle infarction was the only finding. The brachiocephalic arch was thickened in this case, but histology failed to confirm fungal arteritis. In light of the previous nine cases, fungal infiltration and subsequent thrombosis were suspected in the seven cases with concurrent Aspergillus infections. Vascular lesions could not be confirmed.

Our findings suggest that unilateral pectoral muscle infarction due to fungal arteritis may be a differential for unilateral wing droop in passerine birds. Care should be taken to examine the great vessels, brachiocephalic arch and axillary arteries in cases where unilateral pectoral muscle changes are detected at necropsy and possibly in cases of suspected respiratory aspergillosis.

Literature Cited

1.  Chandler F.W., W. Kaplan, and L. Ajello. Color Atlas and Text of the Histopathology of Mycotic Diseases. 1980. Year Book Medical Publishers, Inc., Chicago, IL, 34–38.